COASTAL ZONE MANAGEMENT NOTES - SCET CIVILvetscetcivil.weebly.com/uploads/1/3/2/7/13271550/... · COSTAL ZONE MANAGEMENT NOTES BY CAPT.THIYAGU CREATED BY CAPT.THIYAGARAJU BALASUBRAMANIAM

COSTAL ZONE MANAGEMENT NOTES BY CAPT.THIYAGU

CREATED BY CAPT.THIYAGARAJU BALASUBRAMANIAM

A coastline or a seashore is the area where land meets the sea or ocean.[1] A precise line that can be called a coastline cannot be determined due to the Coastline paradox.

The term "coastal zone" is a region where interaction of the sea and land processes occurs.[2] Both the terms coast and coastal are often used to describe a geographic location or region; for example, New Zealand's West Coast, or the East and West Coasts of the United States.

A pelagic coast refers to a coast which fronts the open ocean, as opposed to a more sheltered coast in a gulf or bay. A shore, on the other hand, can refer to parts of the land which adjoin any large body of water, including oceans (sea shore) and lakes (lake shore). Similarly, the somewhat related term "bank" refers to the land alongside or sloping down to a river (riverbank) or to a body of water smaller than a lake. "Bank" is also used in some parts of the world to refer to an artificial ridge of earth intended to retain the water of a river or pond; in other places this may be called a levee.

While many scientific experts might agree on a common definition of the term "coast", the delineation of the extents of a coast differ according to jurisdiction, with many scientific and government authorities in various countries differing for economic and social policy reasons. According to the UN atlas, 44% of people live within 150 kilometres (93 miles) of the sea.[3]

Human impacts

Human uses of coasts

A settled coastline in Marblehead, Massachusetts. Once a fishing port, the harbor is now dedicated to tourism and pleasure boating. Observe that the sand and rocks have been darkened by oil slick up to the high-water line.

This stretch of coast in Tanzania's capital Dar es Salaam serves as a public waste dump.



Houses close to the coast, like these in Tiburon, California, may be especially desirable properties.

View of sea coast from top of a hill at Visakhapatnam in India

More and more of the world's people live in coastal regions.[6] Many major cities are on or near good harbors and have port facilities. Some landlocked places have achieved port status by building canals.

The coast is a frontier that nations have typically defended against military invaders, smugglers and illegal migrants. Fixed coastal defenses have long been erected in many nations and coastal countries typically have a navy and some form of coast guard.

Coasts, especially those with beaches and warm water, attract tourists. In many island nations such as those of the Mediterranean, South Pacific and Caribbean, tourism is central to the economy. Coasts offer recreational activities such as swimming, fishing, surfing, boating, and sunbathing. Growth management can be a challenge for coastal local authorities who often struggle to provide the infrastructure required by new residents.

Threats to a coast

Coasts also face many human-induced environmental impacts. The human influence on climate change is thought to contribute to an accelerated trend in sea level rise which threatens coastal habitats.

Pollution can occur from a number of sources: garbage and industrial debris; the transportation of petroleum in tankers, increasing the probability of large oil spills; small oil spills created by large and small vessels, which flush bilge water into the ocean.

Fishing has declined due to habitat degradation, overfishing, trawling, bycatch and climate change. Since the growth of global fishing enterprises after the 1950s, intensive fishing has spread from a few concentrated areas to encompass nearly all fisheries. The scraping of the ocean floor in bottom dragging is devastating to coral, sponges and other long-lived species that do not recover quickly. This destruction alters the functioning of the ecosystem and can



permanently alter species composition and biodiversity. Bycatch, the capture of unintended species in the course of fishing, is typically returned to the ocean only to die from injuries or exposure. Bycatch represents about a quarter of all marine catch. In the case of shrimp capture, the bycatch is five times larger than the shrimp caught.

It is believed that melting Arctic ice will cause sea levels to rise and flood costal areas.

Further information: Marine pollution and Marine debris

Conservation

Extraordinary population growth in the 20th century has placed stress on the planet's ecosystems. For example, on Saint Lucia, harvesting mangrove for timber and clearing for fishing reduced the mangrove forests, resulting in a loss of habitat and spawning grounds for marine life that was unique to the area. These forests also helped to stabilize the coastline. Conservation efforts since the 1980s have partially restored the ecosystem.

Types of coast

According to one principle of classification, an emergent coastline is a coastline which has experienced a fall in sea level, because of either a global sea level change, or local uplift. Emergent coastlines are identifiable by the coastal landforms, which are above the high tide mark, such as raised beaches. In contrast, a submergent coastline is one where the sea level has risen, due to a global sea level change, local subsidence, or isostatic rebound. Submergent coastlines are identifiable by their submerged, or "drowned" landforms, such as rias (drowned valleys) and fjords.

Further information: Emergent coastline and Submergent coastline

According to a second principle of classification, a concordant coastline is a coastline where bands of different rock types run parallel to the shore. These rock types are usually of varying resistance, so the coastline forms distinctive landforms, such as coves. Discordant coastlines feature distinctive landforms because the rocks are eroded by ocean waves. The less resistant rocks erode faster, creating inlets or bays; the more resistant rocks erode more slowly, remaining as headlands or outcroppings.

Further information: Concordant coastline and Discordant coastline

Other coastal categories:

• A cliffed coast or abrasion coast is one where marine action has produced steep declivities known as cliffs.

• A flat coast is one where the land gradually descends into the sea. • A graded shoreline is one where wind and water action has produced a flat and

straight coastline.

Coastal landforms



Coastal landforms. The feature shown here as a of Britain, be called a cove. That between the cuspate foreland and the tombolo is a Brbay.

The following articles describe some coastal landforms

• Bay • Cape • Cove

•

•

•

Cliff erosion

• Much of the sediment deposited along a coast is the result of erosion of a surrounding cliff, or bluff. Sea cliffsslopes by waves. If the slope/cliff being undercut is made of unconsolidated sediment it will erode at a much faster ra

• A natural arch is formed when a sea stacks is eroded through by • Sea caves are made when certain rock beds are more susceptible to erosion than the

surrounding rock beds because of different areas of weakness. These areas are eroded at a faster pace creating a hole or crevasse that, through time, by means of wave action and erosion, becomes a cave.

• A stack is formed when a headland is eroded away by wave and wind• A stump is a shortened sea stack that has been eroded away or fallen because of

instability. • Wave-cut notches are caused by the undercutting of overhanging slope

to increased stress on cliff material and a greater probability that the slope material will fall. The fallen debris accumulates at the bottom of the cliff and is eventually removed by waves.

• A wave-cut platform forms after erosion and retreat of a sea cliff has been occurring for a long time. Gently sloping waveof cliff retreat. Later the length of the platenergy as they break further off shore.

Coastal Regulation Zone (CRZ)

The distance upto which development along rivers, creeks an

regulated shall be governed by the distance upto which the tidal effect of sea is

experienced in rivers, creeks or back

identified in the Coastal Zone Management Plans.

2. Prohibited Activities:



Coastal landforms. The feature shown here as a bay would, in certain (mainly southern) parts

. That between the cuspate foreland and the tombolo is a Br

The following articles describe some coastal landforms

Gulf Headland Peninsula

Much of the sediment deposited along a coast is the result of erosion of a surrounding Sea cliffs retreat landward because of the constant undercutting of

slopes by waves. If the slope/cliff being undercut is made of unconsolidated sediment it will erode at a much faster rate then a cliff made of bedrock.[5]

is formed when a sea stacks is eroded through by waves.are made when certain rock beds are more susceptible to erosion than the

surrounding rock beds because of different areas of weakness. These areas are eroded ace creating a hole or crevasse that, through time, by means of wave

action and erosion, becomes a cave. is formed when a headland is eroded away by wave and windis a shortened sea stack that has been eroded away or fallen because of

cut notches are caused by the undercutting of overhanging slopeto increased stress on cliff material and a greater probability that the slope material will fall. The fallen debris accumulates at the bottom of the cliff and is eventually

forms after erosion and retreat of a sea cliff has been occurring for a long time. Gently sloping wave-cut platforms develop early on in the first stages of cliff retreat. Later the length of the platform decreases because the waves lose their energy as they break further off shore.[5]

Coastal Regulation Zone (CRZ)

The distance upto which development along rivers, creeks and back-waters is to be


experienced in rivers, creeks or back-waters, as the case may be, and should be clearly

identified in the Coastal Zone Management Plans.1

ertain (mainly southern) parts . That between the cuspate foreland and the tombolo is a British

Much of the sediment deposited along a coast is the result of erosion of a surrounding retreat landward because of the constant undercutting of

slopes by waves. If the slope/cliff being undercut is made of unconsolidated sediment

waves. are made when certain rock beds are more susceptible to erosion than the

surrounding rock beds because of different areas of weakness. These areas are eroded ace creating a hole or crevasse that, through time, by means of wave

is formed when a headland is eroded away by wave and wind action. is a shortened sea stack that has been eroded away or fallen because of

cut notches are caused by the undercutting of overhanging slopes which leads to increased stress on cliff material and a greater probability that the slope material will fall. The fallen debris accumulates at the bottom of the cliff and is eventually

forms after erosion and retreat of a sea cliff has been occurring cut platforms develop early on in the first stages

form decreases because the waves lose their

waters is to be


waters, as the case may be, and should be clearly



The following activities are declared as prohibited within the Coastal Regulation Zone, namely:

i. setting up of new industries and expansion of existing industries, except (a)10 those directly related to water front or directly needing foreshore facilities and (b) Projects of Department of Atomic Energy;10

i. manufacture or handling or storage or disposal of hazardous substances as specified in the Notifications of the Government of India in the Ministry of Environment and Forests No. S.O. 594(E) dated 28th July 1989, S.O. 966(E) dated 27th November, 1989 and GSR 1037(E) dated 5th December, 1989; except transfer of hazardous substances from ships to ports,

terminals and refineries and vice versa in the port areas:3

Provided that, facilities for receipt and

storage of petroleum products and Liquefied

Natural Gas as specified in Annexure-III

appended to this notification and facilities for

regasification of Liquefied Natural Gas, may

be permitted within the said Zone in areas

not classified as CRZ-I (i), subject to

implementation of safety regulations

including guidelines issued by the Oil

Industry Safety Directorate in the

Government of India, Ministry of Petroleum

and Natural Gas and guidelines issued by the

Ministry of Environment and Forests and

subject to such further terms and conditions

for implementation of ameliorative and

restorative measures in relation to the

environment as may be stipulated by the

Government of India in the Ministry of

Environment and Forests

(iii) Setting up and expansion of fish processing units including warehousing (excluding hatchery and natural fish drying in permitted areas);

Provided that existing fish processing units for modernisation purposes

may utilise twenty five per cent additional plinth area required for

additional equipment and pollution control measures only subject to

existing Floor Space index/ Floor Area Ratio norms and subject to the

condition that the additional plinth area shall not be towards seaward

side of existing unit and also subject to the approval of State Pollution

Control Board or Pollution Control Committee.

i. setting up and expansion of units/mechanism for disposal of waste and effluents, except facilities required for discharging treated effluents into the water course with approval under the



Water (Prevention and Control of Pollution) Act, 1974; and except for storm water drains;

ii. discharge of untreated wastes and effluents from industries, cities or towns and other human settlements. Schemes shall be implemented by the concerned authorities for phasing out the existing practices, if any, within a reasonable time period not exceeding three years from the date of this notification;

(vi) dumping of city or town waste for the purposes of landfilling or otherwise; the existing practice, if any, shall be phased out within a reasonable time not exceeding three years from the date of this Notification;

i. dumping of ash or any wastes from thermal power stations; ii. Land reclamation, bunding or disturbing the natural course of

sea water except those required for construction or modernisation or expansion of ports, harbours, jetties, wharves, quays, slipways, bridges and sea-links and for other facilities that are essential for activities permissible under the notification or for control of coastal erosion and maintenance or clearing of water ways, channels and ports or for prevention of sandbars or for tidal regulators, storm water drains or for structures for prevention of salinity ingress and sweet water recharge:

provided that reclamation for commercial purposes such as

shopping and housing complexes, hotels and entertainment

activities shall not be permissible;

iii. Mining of sands, rocks and other substrata materials, except (a) those rare minerals not available outside the CRZ areas and (b) exploration and extraction of Oil and Natural Gas

Provided that in the Union Territory of the Andaman and

Nicobar islands, mining of sands may be permitted by the

Committee which shall be constituted by the Lieutenant

Governor of the Andaman and Nicobar Islands consisting

of Chief Secretary; Secretary, Department of Environment;

Secretary, Department of Water Resources; and Secretary,

Public Works Department. The said Committee may permit

mining of sand from non-degraded areas for construction

purposes from selected sites, in a regulated manner on a

case to case basis, for a period upto the 30th day of

September, 2002. The quantity of sand mined shall not

exceed the essential requirements for completion of

construction works including dwelling units, shops in

respect of half yearly requirements of 2001-2002 and 2002-

2003 annual plans. The permission for mining of sand may

be given on the basis of a mining plan from such sites and in



such quantity which shall not have adverse impacts on the

environment.

iv. harvesting or drawal of ground water and construction of mechanisms therefor within 200 m of HTL; in the 200m to 500m zone it shall be permitted only when done manually through ordinary wells for drinking, horticulture, agriculture and fisheries;

Provided that drawal of ground water is permitted, where

no other source of water is available and when done

manually through ordinary wells or hand pumps, for

drinking and domestic purposes, in the zone between 50 to

200 m from High Tide Line in case of seas, bays and

estuaries and within 200 m or the CRZ, whichever is less,

from High Tide Line in case of rivers, creeks and

backwaters subject to such restrictions as may be deemed

necessary, in areas affected by sea water intrusion, that

may be imposed by an authority designated by State

Government/Union Territory Administration.

v. construction activities in CRZ -I except as specified in Annexure -I of this notification;

vi. any construction activity between the Low Tide Line and High Tide Line except facilities for carrying treated effluents and waste water discharges into the sea, facilities for carrying sea water for cooling purposes, oil, gas and similar pipelines and facilities essential for activities permitted under this Notification; and

vii. dressing or altering of sand dunes, hills, natural features including landscape changes for beautification, recreational and other such purpose, except as permissible under this Notification.

2. Regulation of Permissible Activities:

All other activities, except those prohibited in para 2 above, will be regulated as under:

1. Clearance shall be given for any activity within the Coastal Regulation Zone only if it requires water front and foreshore facilities.

2. The following activities will require environmental clearance from the Ministry of Environment and Forests, Government of India, namely:

i. Construction activities related to projects of Department of Atomic Energy or Defence requirements for which foreshore facilities are essential such as. slipways, jetties, wharves,



quays; except for classified operational component of defence projects for which a separate procedure shall be followed. (Residential buildings, office buildings, hospital complexes, workshops shall not come within the definition of operational requirements except in very special cases and hence shall not normally be permitted in the CRZ;

ii. Operational constructions for ports and harbours and light houses and constructions for activities such as jetties, wharves, quays and slipways, pipelines, conveying systems including

transmission lines;

(ii) a Exploration and extraction of oil and natural gas and all associated activities and

facilities thereto;

iii. Thermal Power Plants (only foreshore facilities for transport of raw materials facilities for intake of cooling water and outfall for discharge of treated waste water/cooling water); and

iv. All other activities with investment exceeding rupees five crores except those activities which are to be regulated by the concerned

authorities at the State/Union Territory level

in accordance with the provisions of

paragraph 6, sub-paragraph (2) of Annexure

1 of the notification.

(3) (i) The Coastal States and Union Territory Administrations shall prepare, within a period of one year from the date of this Notification, Coastal Zone Management Plans identifying and classifying the CRZ areas within their respective territories in accordance with the guidelines given in Annexures I and II of the Notification and obtain approval (with or without modifications) of the Central Government in the Ministry of Environment & Forests;

(ii) Within the framework of such approved plans, all development and activities within the CRZ other than those covered in para 2 and para 3(2) above shall be regulated by the State Government, Union Territory Administration or the local authority as the case may be in



accordance with the guidelines given in Annexure-I and II of the Notification; and

i. In the interim period till the Coastal Zone management Plans mentioned in para 3(3) (i) above are prepared and approved, all developments and activities within the CRZ shall not violate the provisions of this Notification. State Governments and Union Territory Administrations shall ensure adherence to these regulations and violations, if any, shall be subject to the provisions of the Environment (Protection) Act, 1986.

2. Procedure for monitoring and enforcement:

The Ministry of Environment & Forests and the Government of State or Union Territory and such other authorities at the State or Union Territory levels, as may be designated for this purpose, shall be responsible for monitoring and enforcement of the provisions of this notification within their respective jurisdictions.

Beach Profile:

A beach is a landform along the coast of an ocean, sea, lake, or river. It usually consists of loose particles, which are often composed of rock, such as sand, gravel, shingle, pebbles, or cobblestones. The particles comprising a beach are occasionally biological in origin, such as mollusc shells or coralline algae.

Some beaches have man-made infrastructure, such as lifeguard posts, changing rooms, and showers. They may also have hospitality venues (such as resorts, camps, hotels, and restaurants) nearby. Wild beaches, also known as undeveloped or undiscovered beaches, are not developed in this manner. Wild beaches can be valued for their untouched beauty and preserved nature.

Beaches typically occur in areas along the coast where wave or current action deposits and reworks sediments.

A coastal profile consisting of sand is continuously being modified by the action of the incoming waves, particularly in the surf and breaker zone, where bars can be built up, shifted about or leveled out by the wave-induced cross-shore sediment transport. Prediction of the profile development is important because its shape determines the wave decay and because its development is an integral part of the coastal erosion process. Further, the shape of the profile is important for the distribution and the magnitude of the longshore current and sediment transport, which is also a key factor in the coastal erosion or accretion. A considerable research effort has been made on the processes of cross-shore transport, but it has proven to be difficult to quantify because the mean cross-shore discharge is zero and the transport is composed of several opposing contributions that may be of the same order of magnitude. Outside the surf zone many contributions related to non-linear effects in the wave boundary layer have been identified, such as: streaming in the boundary layer, drift of suspended sediment, effects of higher harmonics in the wave orbital motion and effects



related to wave groups and bound or free long waves. Read More: http://ascelibrary.org/doi/abs/10.1061/40549%28276%29235

As ocean surface waves come closer to shore they break, forming the foamy, bubbly surface we call

surf. The region of breaking waves defines the surf zone. After breaking in the surf zone, the waves

(now reduced in height) continue to move in, and they run up onto the sloping front of the beach,

forming an uprush of water called swash. The water then runs back again as backswash. The

nearshore zone where wave water comes onto the beach is the surf zone. The water in the breaker

zone, or surf zone, is shallow, usually between 5 and 10 m (16 and 33 ft) deep; this causes the waves

to be unstable.

Animal life

The animals that often are found living in the surf zone are crabs, clams, and snails. Surf clams and mole crabs are two species that stand out as inhabitants of the surf zone. Both of these animals are very fast burrowers. The surf clam, also known as the variable coquina, is a filter feeder that uses its gills to filter microalgae, tiny zooplankton, and small particulates out of seawater. The mole crab is a suspension feeder that eats by capturing zooplankton with its antennae. All of these creatures burrow down into the sand to escape from being pulled into the ocean from the tides and waves. They also burrow themselves in the sand to protect themselves from predators. The surf zone is full of nutrients, oxygen, and sunlight which leaves the zone very productive with animal life.

Tides

Rip current in the ocean. Rip currents are often very difficult to spot with one's bare eyes, take caution in any body of water

The Surf Zone can help determine the danger level of rip currents. Rip Current Outlooks use the following set of qualifications:

1. Low Risk rip currents: Wind and/or wave conditions are not expected to support the development of rip currents; however, rip currents can sometimes occur, especially in the vicinity of jetties and piers. Know how to swim and heed the advice of lifeguards.

2. Moderate Risk rip currents:Wind and/or wave conditions support stronger or more frequent rip currents. Only experienced surf swimmers should enter the water.



3. High Risk rip currents: Wind and/or wave conditions support dangerous rip currents. Rip currents are life-threatening to anyone entering the surf.

Offshore:

situated at sea some distance from the shore.

Coastal Waters

Territorial waters, or a territorial sea, as defined by the 1982 United Nations Convention on the Law

of the Sea, is a belt of coastal waters extending at most 12 nautical miles (22.2 km; 13.8 mi) from the

baseline (usually the mean low-water mark) of a coastal state.

Estuary

An estuary is a partly enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea.[1]

Estuaries form a transition zone between river environments and maritime environments and are subject to both marine influences--such as tides, waves, and the influx of saline water--and riverine influences, such as flows of fresh water and sediment. The inflows of both sea water and fresh water provide high levels of nutrients in both the water column and sediment, making estuaries among the most productive natural habitats in the world.[2]

Most existing estuaries were formed during the Holocene epoch by the flooding of river-eroded or glacially scoured valleys when the sea level began to rise about 10,000-12,000 years ago.[3] Estuaries are typically classified by their geomorphological features or by water circulation patterns and can be referred to by many different names, such as bays, harbors, lagoons, inlets, or sounds, although some of these water bodies do not strictly meet the above definition of an estuary and may be fully saline.

The banks of many estuaries are amongst the most heavily populated areas of the world, with about 60% of the world's population living along estuaries and the coast. As a result, many estuaries are suffering degradation by many factors, including sedimentation from soil erosion from deforestation, overgrazing, and other poor farming practices; overfishing; drainage and filling of wetlands; eutrophication due to excessive nutrients from sewage and animal wastes; pollutants including heavy metals, polychlorinated biphenyls, radionuclides and hydrocarbons from sewage inputs; and diking or damming for flood control or water diversion.[3]

Definition



Hudson River estuary waterways around River, 3. Long Island Sound, 4. Bay, separated from Upper New York Bay by Atlantic Ocean.

River Exe estuary

River Nith estuary

Estuary mouth located in Darwin



estuary waterways around New York City, USA: 1. Hudson River, 2.

, 4. Newark Bay, 5. Upper New York Bay, 6. Lower New York New York Bay by the Narrows strait, 7. Jamaic

Darwin, Northern Territory, Australia

: 1. Hudson River, 2. East Lower New York

Jamaica Bay, and 8.



A crowded estuary mouth in Paravur

Estuary mouth

Río de la Plata estuary

Estuary mouth of the Yachats River

Amazon estuary

The word "estuary" is derived from the Latin word which in itself is derived from the term definitions proposed to describe an estuary. The most widely accepted definition is: "a semi



Paravur near the city of Kollam, India

Yachats River in Yachats, Oregon

The word "estuary" is derived from the Latin word aestuarium meaning tidal inlet of the sea, which in itself is derived from the term aestus, meaning tide. There have been many

describe an estuary. The most widely accepted definition is: "a semi

meaning tidal inlet of the sea, , meaning tide. There have been many

describe an estuary. The most widely accepted definition is: "a semi-



enclosed coastal body of water, which has a free connection with the open sea, and within sea water is measurably diluted with freshwater derived from land drainage".[1] However, this definition excludes a number of coastal water bodies such as coastal lagoons and brackish seas. A more comprehensive definition of an estuary is "a semi-enclosed body of water connected to the sea as far as the tidal limit or the salt intrusion limit and receiving freshwater runoff; however the freshwater inflow may not be perennial, the connection to the sea may be closed for part of the year and tidal influence may be negligible".[3] This broad definition also includes fjords, lagoons, river mouths, and tidal creeks. An estuary is a dynamic ecosystem with a connection with the open sea through which the sea water enters with the rhythm of the tides. The sea water entering the estuary is diluted by the fresh water flowing from rivers and streams. The pattern of dilution varies between different estuaries and depends on the volume of fresh water, the tidal range, and the extent of evaporation of the water in the estuary.[2]

Classification based on geomorphology

Drowned river valleys

Main article: Ria

Their width-to-depth ratio is typically large, appearing wedge-shaped in the inner part and broadening and deepening seaward. Water depths rarely exceed 30 m (100 ft). Examples of this type of estuary in the U.S. are the Hudson River, Chesapeake Bay, and Delaware Bay along the Mid-Atlantic coast; and along the Gulf coast, Galveston Bay and Tampa Bay.[4] San Francisco Bay is another good example of a drowned river valley.

Lagoon-type or bar-built

These estuaries are semi-isolated from ocean waters by barrier beaches (barrier islands and barrier spits). Formation of barrier beaches partially encloses the estuary, with only narrow inlets allowing contact with the ocean waters. Bar-built estuaries typically develop on gently sloping plains located along tectonically stable edges of continents and marginal sea coasts. They are extensive along the Atlantic and Gulf coasts of the U.S. in areas with active coastal deposition of sediments and where tidal ranges are less than 4 m (13 ft). The barrier beaches that enclose bar-built estuaries have been developed in several ways:

• building up of offshore bars by wave action, in which sand from the sea floor is deposited in elongated bars parallel to the shoreline,

• reworking of sediment discharge from rivers by wave, current, and wind action into beaches, overwash flats, and dunes,

• engulfment of mainland beach ridges (ridges developed from the erosion of coastal plain sediments around 5000 years ago) due to sea level rise and resulting in the breaching of the ridges and flooding of the coastal lowlands, forming shallow lagoons, and

• elongation of barrier spits from the erosion of headlands due to the action of longshore currents, with the spits growing in the direction of the littoral drift.

Barrier beaches form in shallow water and are generally parallel to the shoreline, resulting in long, narrow estuaries. The average water depth is usually less than 5 m (16 ft), and rarely



exceeds 10 m (33 ft). Examples of bar-built estuaries are Barnegat Bay, New Jersey; Laguna Madre,[5] Texas; and Pamlico Sound, North Carolina.

Fjord-type

Fjord-type estuaries are formed in deeply eroded valleys formed by glaciers. These U-shaped estuaries typically have steep sides, rock bottoms, and underwater sills contoured by glacial movement. The estuary is shallowest at its mouth, where terminal glacial moraines or rock bars form sills that restrict water flow. In the upper reaches of the estuary, the depth can exceed 300 m (1,000 ft). The width-to-depth ratio is generally small. In estuaries with very shallow sills, tidal oscillations only affect the water down to the depth of the sill, and the waters deeper than that may remain stagnant for a very long time, so there is only an occasional exchange of the deep water of the estuary with the ocean. If the sill depth is deep, water circulation is less restricted, and there is a slow but steady exchange of water between the estuary and the ocean. Fjord-type estuaries can be found along the coasts of Alaska, the Puget Sound region of western Washington state, British Columbia, eastern Canada, Greenland, Iceland, New Zealand, and Norway.

Tectonically produced

These estuaries are formed by subsidence or land cut off from the ocean by land movement associated with faulting, volcanoes, and landslides. Inundation from eustatic sea level rise during the Holocene Epoch has also contributed to the formation of these estuaries. There are only a small number of tectonically produced estuaries; one example is the San Francisco Bay, which was formed by the crustal movements of the San Andreas fault system causing the inundation of the lower reaches of the Sacramento and San Joaquin rivers.[6]

Classification based on water circulation

See also: Estuarine water circulation

Salt wedge

In this type of estuary, river output greatly exceeds marine input and tidal effects have a minor importance. Fresh water floats on top of the seawater in a layer that gradually thins as it moves seaward. The denser seawater moves landward along the bottom of the estuary, forming a wedge-shaped layer that is thinner as it approaches land. As a velocity difference develops between the two layers, shear forces generate internal waves at the interface, mixing the seawater upward with the freshwater. An example of a salt wedge estuary is the Mississippi River.[6]

Partially mixed

As tidal forcing increases, river output becomes less than the marine input. Here, current induced turbulence causes mixing of the whole water column such that salinity varies more longitudinally rather than vertically, leading to a moderately stratified condition. Examples include the Chesapeake Bay and Narragansett Bay.[6]

Vertically homogenous



Tidal mixing forces exceed river output, resulting in a well mixed water column and the disappearance of the vertical salinity gradient. The freshwater-seawater boundary is eliminated due to the intense turbulent mixing and eddy effects. The lower reaches of Delaware Bay and the Raritan River in New Jersey are examples of vertically homogenous estuaries.[6]

Inverse

Inverse estuaries occur in dry climates where evaporation greatly exceeds the inflow of fresh water. A salinity maximum zone is formed, and both riverine and oceanic water flow close to the surface towards this zone.[7] This water is pushed downward and spreads along the bottom in both the seaward and landward direction.[3] An example of an inverse estuary is Spencer Gulf, South Australia.

Intermittent

Estuary type varies dramatically depending on freshwater input, and is capable of changing from a wholly marine embayment to any of the other estuary types.[8][9]

Physiochemical variation

The most important variable characteristics of estuary water are the concentration of dissolved oxygen, salinity and sediment load. There is extreme spatial variability in salinity, with a range of near zero at the tidal limit of the tributary river(s) to 3.4% at the estuary mouth. At any one point the salinity will vary considerably over time and seasons, making it a harsh environment for organisms. Sediment often settles in intertidal mudflats which are extremely difficult to colonize. No points of attachment exist for algae, so vegetation based habitat is not established.[clarification needed] Sediment can also clog feeding and respiratory structures of species, and special adaptations exist within mudflat species to cope with this problem. Lastly, dissolved oxygen variation can cause problems for life forms. Nutrient-rich sediment from man-made sources can promote primary production life cycles, perhaps leading to eventual decay removing the dissolved oxygen from the water; thus hypoxic or anoxic zones can develop.[10]

Implications for marine life

Estuaries provide habitats for a large number of organisms and support very high productivity. Estuaries provide habitats for many fish nurseries, depending upon their locations in the world, such as salmon and sea trout.[11] Also, migratory bird populations, such as the black-tailed godwit, Limosa limosa islandica[12] make essential use of estuaries.

Two of the main challenges of estuarine life are the variability in salinity and sedimentation. Many species of fish and invertebrates have various methods to control or conform to the shifts in salt concentrations and are termed osmoconformers and osmoregulators. Many animals also burrow to avoid predation and to live in the more stable sedimental environment. However, large numbers of bacteria are found within the sediment which have a very high oxygen demand. This reduces the levels of oxygen within the sediment often resulting in partially anoxic conditions, which can be further exacerbated by limited water flux.



Phytoplankton are key primary producers in estuaries. They move with the water bodies and can be flushed in and out with the tides. Their productivity is largely dependent upon the turbidity of the water. The main phytoplankton present are diatoms and dinoflagellates which are abundant in the sediment.

It is important to remember that a primary source of food for many organisms on estuaries, including bacteria, is detritus from the settlement of the sedimentation.

Human impact

Of the thirty-two largest cities in the world, twenty-two are located on estuaries.[13] For example, New York City is located at the mouth of the Hudson River estuary.[14]

As ecosystems, estuaries are under threat from human activities such as pollution and overfishing. They are also threatened by sewage, coastal settlement, land clearance and much more. Estuaries are affected by events far upstream, and concentrate materials such as pollutants and sediments.[15] Land run-off and industrial, agricultural, and domestic waste enter rivers and are discharged into estuaries. Contaminants can be introduced which do not disintegrate rapidly in the marine environment, such as plastics, pesticides, furans, dioxins, phenols and heavy metals.

Such toxins can accumulate in the tissues of many species of aquatic life in a process called bioaccumulation. They also accumulate in benthic environments, such as estuaries and bay muds: a geological record of human activities of the last century.

For example, Chinese and Russian industrial pollution, such as phenols and heavy metals, has devastated fish stocks in the Amur River and damaged its estuary soil.[16]

Estuaries tend to be naturally eutrophic because land runoff discharges nutrients into estuaries. With human activities, land run-off also now includes the many chemicals used as fertilizers in agriculture as well as waste from livestock and humans. Excess oxygen-depleting chemicals in the water can lead to hypoxia and the creation of dead zones.[17] This can result in reductions in water quality, fish, and other animal populations.

Overfishing also occurs. Chesapeake Bay once had a flourishing oyster population which has been almost wiped out by overfishing. Oysters filter these pollutants, and either eat them or shape them into small packets that are deposited on the bottom where they are harmless. Historically the oysters filtered the estuary's entire water volume of excess nutrients every three or four days. Today that process takes almost a year,[18] and sediment, nutrients, and algae can cause problems in local waters.

Estuaries along the coast of India

An estuary is a channel that has the sea at one end and a river at the other; in an estuary, seawater is appreciably diluted. The complete salinity range from 0-35 ppt is seen from the head (river end) to the mouth (sea end) of an estuary. About 100 such channels of varying sizes and shapes occur along the coast of India. Each estuary receives its freshwater from



drainage channels of a river basin. The major river basins of India are shown in Fig. 28 together with some of the major riverine/estuarine channels. The banks of estuarine channels form a favoured location for human settlements, which use the estuaries for fishing and commerce, but nowadays also for dumping civic and industrial waste. Estuaries are usually biologically highly productive zones. They also act as a filter for some dissolved constituents in river water; these precipitate in the zone where river water meets seawater. More important is the trapping of suspended mud and sand carried by rivers which leads to delta formations around estuaries. Major estuaries occur in the Bay of Bengal. Many estuaries

are locations of some of the major seaports. Most of the India’s major estuaries occur on the east coast. In contrast, the estuaries on the west coast are smaller. Two typical examples of estuaries on the west coast are the Mandovi and Zuari estuaries located to the north and south of the main campus of the National Institute of Oceanography at Dona Paula, Goa.

The following 10 pages are in this category, out of 10 total. This list may not reflect recent changes (learn more).

B

• Baga Creek

C

• Chilika Lake

E

• Ennore creek

K Kerala backwaters

P

• Panvel Creek • Paravur, Kollam

S

• Sir Creek • St Inez Creek

T

• Thekkumbhagam • Trans Thane Creek



Ennore creek is a backwater located in Ennore, Chennai along the Coromandel Coast of the Bay of

Bengal. It is located in the zone comprising lagoons with salt marshes and backwaters, submerged

under water during high tide and forming an arm of the sea with the opening to the Bay of Bengal at

the creek. The zone is spread over an area of 4 km2,[1]

and the creek covers an area of 2.25 km2.[2]

It

is located 20 km north of the city centre and 2.6 km south of the Ennore Port, and the creek area

stretches 3 km into the sea and 5 km along the coast. The creek is nearly 400 m wide, elongated in

northeast-southwest direction and merging with the backwater bodies. Once a flourishing mangrove

swamp, the creek has been degraded to patches in the fringes mainly due to human activities in the

region. The depth of the creek varies from 1 to 2 m and is shallow near the mouth. The north–south

trending channels of the creek connect it with the Pulicat Lake to the north and to the distributaries

of the Kosasthalaiyar River in the south. The northwestern part of the creek merges with the tidal

flats. The soil in the region is of loamy and alluvial types. Most of the area consists of tracts of

alluvial soil and the eastern region comprises beach dunes, tidal flats and creek. The creek is

oriented from west to east and opens into the Bay of Bengal to the east at Ennore. The creek acts as

an outlet for the excess water from the Poondi Reservoir. The creek separates the town of Ennore

from the Ennore Port located in the north and the Kattupalli Shipyard located further north. The

North Chennai Thermal Power Station is located at the north of the creek and the Ennore Thermal

Power Station is located to the south. The creek is part of the Pulicat water system, including the

Pulicat lagoon and the Buckingham Canal. As per the 1991 Coastal Regulation Zone notification, the

entire Pulicat water system is designated CRZ I.[3]

The creek is experiencing siltation due to

emergence of the Ennore Port.

The Kerala backwaters are a chain of brackish lagoons and lakes lying parallel to the Arabian Sea coast (known as the Malabar Coast) of Kerala state in southern India. The network includes five large lakes linked by canals, both manmade and natural, fed by 38 rivers, and extending virtually half the length of Kerala state. The backwaters were formed by the action of waves and shore currents creating low barrier islands across the mouths of the many rivers flowing down from the Western Ghats range.

Ashtamudi Lake is the most visited of the lakes, covering an area of 200 km², and located in Kollam. The lake has a large network of canals that meander through the town. Ashtamudi is also India's most preserved lake[1]

The Kerala Backwaters are a network of interconnected canals, rivers, lakes and inlets, a labyrinthine system formed by more than 900 km of waterways, and sometimes compared to the American Bayou.[2] In the midst of this landscape there are a number of towns and cities, which serve as the starting and end points of backwater cruises.[3] National Waterway No. 3 from Kollam to Kottapuram, covers a distance of 205 km and runs almost parallel to the coast line of southern Kerala facilitating both cargo movement and backwater tourism.[1] The important rivers from north to south are; Valapattanam river (110 km.), Chaliar (69 km.), Kadalundipuzha (130 km.), Bharathapuzha (209 km.), Chalakudy river (130 km.), Periyar (244 km), Pamba (176 km), Achancoil (128 km.) and Kalladayar (121 km.). Other than these, there are 35 more small rivers and rivulets flowing down from the Ghats. Most of these rivers are navigable up to the midland region, in country crafts.

The backwaters have a unique ecosystem - freshwater from the rivers meets the seawater from the Arabian Sea. In certain areas, a barrage has been built near Neendakara Kollam, salt



water from the sea is prevented from entering the deep inside, keeping the fresh water intact. Such fresh water is extensively used for irrigation purposes.[1][4]

Many unique species of aquatic life including crabs, frogs and mudskippers, water birds such as terns, kingfishers, darters and cormorants, and animals such as otters and turtles live in and alongside the backwaters. Palm trees, pandanus shrubs, various leafy plants and bushes grow alongside the backwaters, providing a green hue to the surrounding landscape.[4]

Wetland From Wikipedia, the free encyclopedia

For other uses, see Wetland (disambiguation).

Laguna de Rocha, the largest wetland in the urban area in Esteban Echeverría Partido, Argentina

Mangrove swamps are coastal wetlands. This swamp is in the Florida Everglades.[1]

Peat bogs are freshwater wetlands that develop in areas with standing water and low soil fertility.



Marshes develop along the edges of rivers and lakes.

Many species of frogs live in wetlands, while others visit them each year to lay eggs.

Snapping turtles are one of the many kinds of turtles found in wetlands

A wetland is a land area that is saturated with water, either permanently or seasonally, such that it takes on the characteristics of a distinct ecosystem.[2] Primarily, the factor that distinguishes wetlands from other land forms or water bodies is the characteristic vegetation that is adapted to its unique soil conditions. Wetlands consist primarily of hydric soil, which supports aquatic plants.[3][4]

The water found in wetlands can be saltwater, freshwater, or brackish.[4] Main wetland types include swamps, marshes, bogs and fens.[5] Sub-types include mangrove, carr, pocosin, and varzea.

Wetlands play a number of roles in the environment, principally water purification, flood control, and shoreline stability. Wetlands are also considered the most biologically diverse of all ecosystems, serving as home to a wide range of plant and animal life.[6]

Wetlands occur naturally on every continent except Antarctica.[7] They can also be constructed artificially as a water management tool, which may play a role in the developing field of water-sensitive urban design.



The largest wetlands in the world include the Amazon River basin and the West Siberian Plain.[8] Another large wetland is the Pantanal, which straddles Brazil, Bolivia, and Paraguay in South America.[9]

The UN Millennium Ecosystem Assessment determined that environmental degradation is more prominent within wetland systems than any other ecosystem on Earth. International conservation efforts are being used in conjunction with the development of rapid assessment tools

Definitions

A patch of land that develops pools of water after a rain storm would not be considered a "wetland," even though the land is wet. Wetlands have unique characteristics: they are generally distinguished from other water bodies or landforms based on their water level and on the types of plants that live within them. Specifically, wetlands are characterized as having a water table that stands at or near the land surface for a long enough period each year to support aquatic plants.[10][11]

A more concise definition is a community composed of hydric soil and hydrophytes.[7]

Wetlands have also been described as ecotones, providing a transition between dry land and water bodies.[12] Mitsch and Gosselink write that wetlands exist "...at the interface between truly terrestrial ecosystems and aquatic systems, making them inherently different from each other, yet highly dependent on both."[13]

In environmental decision-making, there are subsets of definitions that are agreed upon to make regulatory and policy decisions.

Technical definitions

A wetland is "an ecosystem that arises when inundation by water produces soils dominated by anaerobic processes, which, in turn, forces the biota, particularly rooted plants, to adapt to flooding."[14] There are four main kinds of wetlands -- marsh, swamp, bog and fen (bogs and fens both being types of mires). Some experts also recognize wet meadows and aquatic ecosystems as additional wetland types.[5] The largest wetlands in the world include the swamp forests of the Amazon and the peatlands of Siberia.[8]

Ramsar Convention definition

Under the Ramsar international wetland conservation treaty, wetlands are defined as follows:[15]

• Article 1.1: "...wetlands are areas of marsh, fen, peatland or water, whether natural or

artificial, permanent or temporary, with water that is static or flowing, fresh, brackish or salt,

including areas of marine water the depth of which at low tide does not exceed six metres."

• Article 2.1: "[Wetlands] may incorporate riparian and coastal zones adjacent to the

wetlands, and islands or bodies of marine water deeper than six metres at low tide lying

within the wetlands."



Regional definitions

Although the general definition given above applies around the world, each county and region tends to have its own definition for legal purposes.In the United States, wetlands are defined as "those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas".[16] This definition has been used in the enforcement of the Clean Water Act. Some US states, such as Massachusetts and New York, have separate definitions that may differ from the federal government's.

In the United States Code (16 U.S.C., Section 3801(a)(18)), the term wetland is defined "as land that (A) has a predominance of hydric soils, (B) is inundated or saturated by surface or groundwater at a frequency and duration sufficient to support a prevalence of hydrophytic vegetation typically adapted for life in saturated soil conditions and C) under normal circumstances supports a prevalence of such vegetation." Related to this legal definitions, the term "normal circumstances" are conditions expected to occur during the wet portion of the growing season under normal climatic conditions (not unusually dry or unusually wet), and in the absence of significant disturbance. It is not uncommon for a wetland to be dry for long portions of the growing season. Wetlands can be dry during the dry season and abnormally dry periods during the wet season, but under normal environmental conditions the soils in a wetland will be saturated to the surface or inundated such that the soils become anaerobic, and those conditions will persist through the wet portion of the growing season.

Ecology

The most important factor producing wetlands is flooding. The duration of flooding determines whether the resulting wetland has aquatic, marsh or swamp vegetation. Other important factors include fertility, natural disturbance, competition, herbivory, burial and salinity.[5] When peat accumulates, bogs and swamps arise.

Characteristics

Wetlands vary widely due to local and regional differences in topography, hydrology, vegetation, and other factors, including human involvement. Wetlands can be divided into two main classes: tidal and non-tidal areas.[7]

Hydrology

Wetland hydrology is associated with the spatial and temporal dispersion, flow, and physiochemical attributes of surface and ground water in its reservoirs. Based on hydrology, wetlands can be categorized as riverine (associated with streams), lacustrine (associated with lakes and reservoirs), and palustrine (isolated). Sources of hydrological flows into wetlands are predominately precipitation, surface water, and ground water. Water flows out of wetlands by evapotranspiration, surface runoff, and sub-surface water outflow. Hydrodynamics (the movement of water through and from a wetland) affects hydroperiods (temporal fluctuations in water levels) by controlling the water balance and water storage within a wetland.[17]



Landscape characteristics control wetland hydrology and hydrochemistry. The O2 and CO2 concentrations of water depend on temperature and atmospheric pressure. Hydrochemistry within wetlands is determined by the pH, salinity, nutrients, conductivity, soil composition, hardness, and the sources of water. Water chemistry of wetlands varies across landscapes and climatic regions. Wetlands are generally minerotrophic with the exception of bogs.

Bogs receive their water from the atmosphere and therefore their water has low mineral ionic composition because ground water has a higher concentration of dissolved nutrients and minerals in comparison to precipitation.

The water chemistry of fens ranges from low pH and low minerals to alkaline with high accumulation of calcium and magnesium because they acquire their water from precipitation as well as ground water.[18]

Role of salinity

Salinity has a strong influence on wetland water chemistry, particularly in wetlands along the coast.[5][19] In non-riverine wetlands, natural salinity is regulated by interactions between ground and surface water, which may be influenced by human activity.[20]

Soil

Carbon is the major nutrient cycled within wetlands. Most nutrients, such as sulfur, phosphorus, carbon, and nitrogen are found within the soil of wetlands. Anaerobic and aerobic respiration in the soil influences the nutrient cycling of carbon, hydrogen, oxygen, and nitrogen,[21] and the solubility of phosphorus[22] thus contributing to the chemical variations in its water. Wetlands with low pH and saline conductivity may reflect the presence of acid sulfates[23] and wetlands with average salinity levels can be heavily influenced by calcium or magnesium. Biogeochemical processes in wetlands are determined by soils with low redox potential.[24]

Biota

The biota of a wetland system includes its vegetation zones and structure as well as animal populations. The most important factor affecting the biota is the duration of flooding.[5] Other important factors include fertility and salinity. In fens, species are highly dependent on water chemistry. The chemistry of water flowing into wetlands depends on the source of water and the geological material in which it flows through[25] as well as the nutrients discharged from organic matter in the soils and plants at higher elevations in slope wetlands.[26] Biota may vary within a wetland due to season or recent flood regimes.

Flora

There are four main groups of hydrophytes that found in wetland systems throughout the world.[27]

Submerged water plants. This type of vegetation is found completely underwater. Submerged wetland vegetation can grow in saline and fresh-water conditions. Some species have underwater flowers, while others have long stems to allow the flowers to reach the surface.[28]



Submerged species provide a food source for native fauna, habitat for invertrebrates, and also possess filtration capabilities. Examples include seagrasses and eelgrass.

Floating water plants. Floating vegetation is usually small although it may take up a large surface area in a wetland system. These hydrophytes have small roots and are only found in slow-moving water with rich-nutrient level water Floating aquatic plants are a food resource for avian species. Examples include water lilies, lily pad and duckweed.

Emergent water plants. Emergent water plants can be seen above the surface of the water but whose roots are completely submerged. Many have aerenchyma to transmit oxygen from the atmosphere to their roots.[29] Extensive areas of emergent plants are usually termed marsh. Examples include cattails (Typha) and arrow arum (Peltandra virginica).

Surrounding trees and shrubs. Forested wetlands are generally known as swamps.[5] The upper level of these swamps is determined by high water levels, which are negatively affected by dams.[30] Some swamps can be dominated by a single species, such as silver maple swamps around the Great Lakes.[31] Others, like those of the Amazon Basin, have large numbers of different tree species.[32] Examples include cypress (Taxodium) and mangrove.

Fauna

Fish: Fish are more dependent on wetland ecosystems than any other type of habitat. 75% of the United States’ commercial fish and shellfish stocks depend solely on estuaries to survive.[6] Tropical fish species need mangroves for critical hatchery and nursery grounds and the coral reef system for food.

Amphibians: Frogs are the most crucial amphibian species in wetland systems. Frogs need both terrestrial and aquatic habitats in which to reproduce and feed. While tadpoles control algal populations, adult frogs forage on insects. Frogs are used as an indicator of ecosystem health due to their thin skin which absorbs both nutrient and toxins from the surrounding environment resulting in an above average extinction rate in unfavorable and polluted environmental conditions.[33]

Reptiles: Alligators and crocodiles are two common reptilian species. Alligators are found in fresh water along with the fresh water species of the crocodile. The saltwater crocodile is found in estuaries and mangroves and can be seen in the coastline bordering the Great Barrier Reef in Australia. The Florida Everglades is the only place in the world where both crocodiles and alligators co-exist.[1] Snakes, lizards, goannas, and turtles also can be seen throughout wetlands. Snapping turtles are one of the many kinds of turtles found in wetlands.

Mammals: Multiple small mammals as well as large herbivore and apex species such as the Florida Panther live within and around wetlands. The wetland ecosystem attracts mammals due to its prominent seed sources, invertebrate populations, and numbers of small reptiles and amphibians.

Monotremes: The platypus (Ornithorhynchus anatinus) is found in eastern Australia living in freshwater rivers or lakes, and much like the beaver creates dams, create burrows for shelter and protection. The platypus swims through the use of webbed feet. Platypuses feed on insect larvae, worms, or other freshwater insects hunting mainly by night by the use of their bill. They turn up mud on the bottom of the lake or river, and with the help of the electroreceptors



located on the bill, unearth insects and freshwater insects. The platypus stores their findings in special pouches behind their bill and consumes its prey upon returning to the surface.[34]

Insects and invertebrates: These species total more than half of the 100,000 known animal species in wetlands. Insects and invertebrates can be submerged in the water or soil, on the surface, and in the atmosphere.

Algae

Algae are diverse water plants that can vary in size, color, and shape. Algae occur naturally in habitats such as inland lakes, inter-tidal zones, and damp soil and provide a dedicated food source for animals, fish, and invertebrates. There are three main groups of algae:

Plankton are algae which are microscopic, free-floating algae. This algae is so tiny that on average, if fifty of these microscopic algae were lined up end-to-end, it would only measure one millimetre. Plankton are the basis of the food web and are responsible for primary production in the ocean using photosynthesis to make food. Filamentous algae are long strands of algae cells that form floating mats. Chara and Nitella algae are upright algae that look like a submerged plant with roots.[35]

Climates

Temperature

Wetlands contrast the hot, arid landscape around Middle Spring, Fish Springs National Wildlife

Refuge, Utah.

Temperatures vary greatly depending on the location of the wetland. Many of the world's wetlands are in temperate zones (midway between the North or South Pole and the equator). In these zones, summers are warm and winters are cold, but temperatures are not extreme. However, wetlands found in the tropic zone, around the equator, are warm year round. Wetlands on the Arabian Peninsula, for example, can reach 50 °C (122 °F) and would therefore be subject to rapid evaporation. In northeastern Siberia, which has a polar climate, wetland temperatures can be as low as −50 °C (−58 °F). In a moderate zone, such as the Gulf of Mexico, a typical temperature might be 11 °C (51 °F). Wetlands are also located in every climatic zone.

Rainfall



The amount of rainfall a wetland receives varies widely according to its area. Wetlands in Wales, Scotland, and Western Ireland typically receive about 1500 mm (or 60 in) per year. In some places in Southeast Asia, where heavy rains occur, they can receive up to 10,000 mm (about 200 in). In the northern areas of North America, wetlands exist where as little as 180 mm (7 inches) of rain fall each year.

Temporal variation:[36]

• Perennial systems

• Seasonal systems

• Episodic (periodic or intermittent) system of the down

• Surface flow may occur in some segments, with subsurface flow in other segments

• Ephemeral (short-lived) systems

• Migratory species

Human-disturbance:[37]

• Encroachment

o Drainage

o Development

o Over-grazing

o Mining

o Unsustainable water use

• Ecosystem Stress

o Water Scarcity

o Endangered species

o Disruption of breeding grounds

o Imbalance in sediment load and nutrient filtration

Peatswamps of South-east Asia

In Southeast Asia, peatswamp forests and soils are being drained, burnt, mined, and overgrazed, contributing severely to climate change.[37] As a result of peat drainage, the organic carbon that was built up over thousands of years and is normally under water is suddenly exposed to the air. It decomposes and turns into carbon dioxide (CO2), which is released into the atmosphere. Peat fires cause the same process to occur and in addition create enormous clouds of smoke that cross international borders, such as happens every year in Southeast Asia. While peatlands constitute only 3% of the world’s land area, their degradation produces 7% of all fossil fuel CO2 emissions.

Through the building of dams, Wetlands International is halting the drainage of peatlands in Southeast Asia, hoping to mitigate CO2 emissions. Concurrent wetland restoration techniques include reforestation with native tree species as well as the formation of community fire brigades. This sustainable approach can be seen in Central Kalimantan and Sumatra, Indonesia.

Aquaculture

Concerns are developing over certain aspects of farm fishing, which uses natural waterways to harvest fish for human consumption and pharmaceuticals. This practice has become



especially popular in Asia and the South Pacific. Its impact upon much larger waterways downstream has negatively affected many small island developing states.[38]

The function of natural wetlands can be classified by their ecosystem benefits. United Nations Millennium Ecosystem Assessment and Ramsar Convention found wetlands to be of biosphere significance and societal importance in the following areas:

• Flood control

• Groundwater replenishment

• Shoreline stabilisation and storm protection

• Water purification

• Reservoirs of biodiversity

• Wetland products

• Cultural values

• Recreation and tourism

• Climate change mitigation and adaptation

The economic worth of the ecosystem services provided to society by intact, naturally functioning wetlands is frequently much greater than the perceived benefits of converting them to ‘more valuable’ intensive land use – particularly as the profits from unsustainable use often go to relatively few individuals or corporations, rather than being shared by society as a whole.-Ramsar convention

Unless otherwise cited, Ecosystem services is based on the following series of references.[6]

Flood control

Major wetland type: floodplain

Storage Reservoirs and Flood Protection. The wetland system of floodplains is formed from major rivers downstream from their headwaters. Notable river systems that produce large spans of floodplain include the Nile River, the Niger river inland delta, [the Zambezi River flood plain], [the Okavango River inland delta],[the Kafue River flood plain][the Lake Bangweulu flood plain] (Africa), Mississippi River (USA), Amazon River (South America), Yangtze River (China), Danube River (Central Europe) and Murray-Darling River (Australia). "The floodplains of major rivers act as natural storage reservoirs, enabling excess water to spread out over a wide area, which reduces its depth and speed. Wetlands close to the headwaters of streams and rivers can slow down rainwater runoff and spring snowmelt so that it doesn’t run straight off the land into water courses. This can help prevent sudden, damaging floods downstream.”[6]

Human-Impact. Converting wetlands through drainage and development have contributed to the issue of irregular flood control through forced adaption of water channels to narrower corridors due to loss of wetland area. These new channels must manage the same amount of precipitation causing flood peaks to be [higher or deeper] and floodwaters to travel faster.

Water management engineering developments in the past century have degraded these wetlands through the construction on artificial embankments. These constructions may be classified as dykes, bunds, levees, weirs, barrages and dams but serve the single purpose of concentrating water into a select source or area. Wetland water sources that were once spread



slowly over a large, shallow area are pooled into deep, concentrated locations. Loss of wetland floodplains results in more severe and damaging flooding. Catastrophic human impact in the Mississippi River floodplains was seen in death of several hundred individuals during a levee breach in New Orleans caused by Hurricane Katrina. Ecological catastrophic events from human-made embankments have been noticed along the Yangtze River floodplains after the where the middle of the river has become prone to more frequent and damaging flooding including the loss of riparian vegetation, a 30% loss of the vegetation cover throughout the river’s basin, a doubling of the percentage of the land affected by soil erosion, and a reduction in reservoir capacity through siltation build-up in floodplain lakes.[6]

Groundwater replenishment

Major wetland type: marsh, swamp, & subterranean karst and cave hydrological systems

The surface water which is the water visibly seen in wetland systems only represents a portion of the overall water cycle which also includes atmospheric water and groundwater. Wetland systems are directly linked to groundwater and a crucial regulator of both the quantity and quality of water found below the ground. Wetland systems that are made of permeable sediments like limestone or occur in areas with highly variable and fluctuating water tables especially have a role in groundwater replenishment or water recharge. Sediments that are porous allow water to filter down through the soil and overlying rock into aquifers which are the source of 95% of the world’s drinking water. Wetlands can also act as recharge areas when the surrounding water table is low and as a discharge zone when it is too high. Karst (cave) systems are a unique example of this system and are a connection of underground rivers influenced by rain and other forms of precipitation. These wetland systems are capable of regulating changes in the water table on upwards of 130 metres (430 ft).

Human-Impact. Groundwater is an important source of water for drinking and irrigation of crops. Over 1 billion people in Asia and 65% of the public water sources in Europe source 100% of their water from groundwater. Irrigation is a massive use of groundwater with 80% of the world’s groundwater used for agricultural production.[6]

Unsustainable abstraction of groundwater has become a major concern. In the Commonwealth of Australia, water licensing is being implemented to control use of the water in major agricultural regions. On a global scale, groundwater deficits and water scarcity is one of the most pressing concerns facing the 21st century.[6]

Shoreline stabilisation and storm protection

Wetland type: Mangroves, Coral Reefs, Saltmarsh

Main article: Integrated Coastal Zone Management

Tidal and inter-tidal wetland systems protect and stabilize coastal zones. Coral reefs provide a protective barrier to coastal shoreline. Mangroves stabilize the coastal zone from the interior and will migrate with the shoreline to remain adjacent to the boundary of the water. The main conservation benefit these systems have against storms and tidal waves is the ability to reduce the speed and height of waves and floodwaters.



Human-Impact. The sheer number of people who live and work near the coast is expected to grow immensely over the next 50 years. From an estimated 200 million people that currently live in low-lying coastal regions, the development of urban coastal centers is projected to increase the population by 5 fold within 50 years.[39] The United Kingdom has begun the concept of managed coastal realignment. This management technique provides shoreline protection through restoration of natural wetlands rather than through applied engineering. In East Asia, reclamation of coastal wetlands has resulted in widespread transformation of the coastal zone, and up to 65% of coastal wetlands have been destroyed by coastal development.[40][41]

Water purification

Wetland Type: Floodplain, Mudflat, Saltmarsh, Mangroves

Nutrient Retention. Wetlands cycle both sediments and nutrients balancing terrestrial and aquatic ecosystems. A natural function of wetland vegetation is the up-take and storage of nutrients found in the surrounding soil and water. These nutrients are retained in the system until the plant dies or is harvested by animals or humans. Wetland vegetation productivity is linked to the climate, wetland type, and nutrient availability. The grasses of fertile floodplains such as the Nile produce the highest yield including plants such as Arundo donax(giant reed), Cyperus papyrus (papyrus), Phragmites (reed) and Typha (cattail, bulrush).

Sediment Traps. Rainfall run-off is responsible for moving sediment through waterways. These sediments move towards larger and more sizable waterways through a natural process that moves water towards oceans. All types of sediments which may be composed of clay, sand, silt, and rock can be carried into wetland systems through this process. Reedbeds or forests located in wetlands act as physical barriers to slow waterflow and trap sediment.

Water purification. Many wetland systems possess biofilters, hydrophytes, and organisms that in addition to nutrient up-take abilities have the capacity to remove toxic substances that have come from pesticides, industrial discharges, and mining activities. The up-take occurs through most parts of the plant including the stems, roots, and leaves . Floating plants can absorb and filter heavy metals. Eichhornia crassipes (water hyacinth), Lemna (duckweed) and Azolla (water fern) store iron and copper commonly found in wastewater. Many fast-growing plants rooted in the soils of wetlands such as Typha (cattail) and Phragmites (reed) also aid in the role of heavy metal up-take. Animals such as the oyster can filter more than 200 liters (53 gallons) of water per day while grazing for food, removing nutrients, suspended sediments, and chemical contaminants in the process.

Capacity. The ability of wetland systems to store nutrients and trap sediment is highly efficient and effective but each system has a threshold. An overabundance of nutrient input from fertilizer run-off, sewage effluent, or non-point pollution will cause eutrophication. Upstream erosion from deforestation can overwhelm wetlands making them shrink in size and see dramatic biodiversity loss through excessive sedimentation load. The capacity of wetland vegetation to store heavy metals is affected by waterflow, number of hectares (acres), climate, and type of plant.

Human-Impact. Introduced hydrophytes in different wetland systems can have devastating results. The introduction of water hyacinth, a native plant of South America into Lake Victoria in East Africa as well as duckweed into non-native areas of Queensland, Australia,



have overtaken entire wetland systems suffocating the ecosystem due to their phenomenal growth rate and ability to float and grow on the surface of the water.

Constructed wetlands

Main article: Constructed wetland

The function of most natural wetland systems is not to manage to wastewater, however, their high potential for the filtering and the treatment of pollutants has been recognized by environmental engineers that specialize in the area of wastewater treatment. These constructed artificial wetland systems are highly controlled environments that intend to mimic the occurrences of soil, flora, and microorganisms in natural wetlands to aid in treating wastewater effluent. Artificial wetlands provide the ability to experiment with flow regimes, micro-biotic composition, and flora in order to produce the most efficient treatment process. Other advantages are the control of retention times and hydraulic channels.[42] The most important factors of constructed wetlands are the water flow processes combined with plant growth. Constructed wetland systems can be surface flow systems with only free-floating macrophytes, floating-leaved macrophytes, or submerged macrophytes; however, typical free water surface systems are usually constructed with emergent macrophytes.[43] Constructed wetlands can be adapted to treat raw sewage, secondary domestic sludge, enhance water quality of oxidation ponds’ discharge, storm waters, mining waste, and industrial and agricultural waste effluents. The Urrbrae Wetland in Australia was constructed for urban flood control and environmental education. International wastewater management programs can be seen from Kolkata (Calcutta), India to Arcata, California, USA.[44]

Kolkata’s constructed wetland. Kolkata is an example of how constructed wetlands are being utilized in developing countries.

Using the purification capacity of wetlands, the Indian city of Kolkata (Calcutta) has pioneered a system of sewage disposal that is both efficient and environmentally friendly. Built to house one million people, Kolkata is now home to over 10 million, many living in slums. But the 8,000-hectare East Kolkata Wetlands Ramsar Site, a patchwork of tree-fringed canals, vegetable plots, rice paddies and fish ponds – and the 20,000 people that work in them – daily transform one-third of the city’s sewage and most of its domestic refuse into a rich harvest of fish and fresh vegetables. For example, the Mudially Fishermen’s Cooperative Society is a collective of 300 families that lease 70 hectares into which wastewater from the city is released. Through a series of natural treatment processes – including the use of Eichhornia crassipes and other plants for absorbing oil, grease and heavy metals – the Cooperative has turned the area into a thriving fish farm and nature park. In 2005/06, the Cooperative sold fish worth over US$135,000 and shared income of more than US$55,000 among its members.[6][not in citation given]

Reservoirs of biodiversity

Wetland systems' rich biodiversity is becoming a focal point at International Treaty Conventions and within the World Wildlife Fund organization due to the high number of species present in wetlands, the small global geographic area of wetlands, the number of species which are endemic to wetlands, and the high productivity of wetland systems. Hundred of thousands of animal species, 20,000 of them vertebrates, are living in wetland systems. The discovery rate of fresh water fish is at 200 new species per year.



Biodiverse river basins. The Amazon holds 3,000 species of fresh water fish species within the boundaries of its basin whose function it is to disperse the seeds of trees. One of its key species, the Piramutaba catfish, Brachyplatystoma vaillantii, migrates more than 3,300 km (2,051 miles) from its nursery grounds near the mouth of the Amazon River to its spawning grounds in Andean tributaries (400 m or 437 yards above sea level) distributing plants seed along the route.

Productive intertidal zones. Intertidal mudflats have a similar productivity even while possessing a low number of species. The abundance of invertebrates found within the mud are a food source for migratory waterfowl.

Critical life-stage habitat. Mudflats, saltmarshes, mangroves, and seagrass beds contain bother species richness and productivity, and are home to important nursery areas for many commercial fish stocks.

Genetic Diversity. Many species in wetland systems are unique due to the long period of time that the ecosystem has been physically isolated from other aquatic sources. The number of endemic species in Lake Baikal in Russia classifies it as a hotspot for biodiversity and one of the most biodiverse wetlands in the entire world.

Lake Baikal. Evidence from a research study by Mazepova et al. suggest that the number of crustacean species endemic to Baikal Lake (>690 species and subspecies) exceeds the number of the same groups of animals inhabiting all the fresh water bodies of Eurasia together. Its 150 species of free-living Platyhelminthes alone is analogous to the entire number in all of Eastern Siberia. The 34 species and subspecies number of Baikal sculpins is more than twice the number of the analogous fauna that inhabits Eurasia. One of most exciting discoveries was made by A.V. Shoshin who registered about 300 species of free-living nematodes using only 6 near-shore sampling localities in the Southern Baikal. "If we will take into consideration, that about 60 % of the animals can be found nowhere else except Baikal, it may be assumed that the lake may be the biodiversity center of the Eurasian continent."[45]

Human Impact. Biodiversity loss occurs in wetland systems through land use changes, habitat destruction, pollution, exploitation of resources, and invasive species. Vulnerable, threatened, and endangered species number at 17% of waterfowl, 38% of fresh-water dependent mammals, 33% of fresh water fish, 26% of fresh water amphibians, 72% of fresh water turtles, 86% of marine turtles, 43% of crocodilians and 27% of coral reef-building species.

The impact of maintaining biodiversity is seen at the local level through job creation, sustainability, and community productivity. A good example is the Lower Mekong basin which runs through Cambodia, Laos, and Vietnam. Supporting over 55 million people, the sustainability of the region is enhanced through wildlife tours. The US state of Florida has estimated that US$ 1.6 billion was generated in state revenue from recreational activities associated with wildlife. Sustainable harvesting for medicinal remedies found in native wetlands plants in the Caribbean and Australia include the Red Mangrove Rhizophora mangle which possesses antibacterial, wound-healing, anti-ulcer effects, and antioxidant properties.[46]

Wetland products



Wetland systems naturally produce an array of vegetation and other ecological products that can harvested for personal and commercial use. The most significant of these is fish which have all or part of their life-cycle occur within a wetland system. Fresh and saltwater fish are the main source of protein for one billion people and comprise 15% of an additional two billion people’s diets. In addition, fish generate a fishing industry that provides 80% of the income and employment to residents in developing countries. Another food staple found in wetland systems is rice, a popular grain that is consumed at the rate of 1/5 of the total global calorie count. In Bangladesh, Cambodia and Vietnam, where rice paddies are predominant on the landscape, rice consumption reach 70%.[46]

Food converted to sweeteners and carbohydrates include the sago palm of Asia and Africa (cooking oil), the nipa palm of Asia (sugar, vinegar, alcohol, and fodder) and honey collection from mangroves. More than supplemental dietary intake, this produce sustains entire villages. Coastal Thailand villages earn the key portion of their income from sugar production while the country of Cuba relocates more than 30,000 hives each year to track the seasonal flowering of the mangrove Avicennia.

Other mangrove-derived products:

• Fuelwood

• Salt (produced by evaporating seawater)

• Animal fodder

• Traditional medicines (e.g. from mangrove bark)

• Fibers for textiles

• Dyes and tannins

Human Impact. Over-fishing is the major problem for sustainable use of wetlands. The field of aquaculture within the fisheries industries is eliminating mass areas of wetland systems through practices seen such as in the shrimp farming industry's destruction of mangroves. Aquaculture is continuing to develop rapidly throughout the Asia-Pacific region specifically in China with world holdings in Asia equal to 90% of the total number of aquaculture farms and 80% of its global value.[46] Threats to rice fields mainly stem from inappropriate water management, introduction of invasive alien species, agricultural fertilizers, pesticides, and land use changes. Industrial-scale production of palm oil threatens the biodiversity of wetland ecosystems in parts of south-east Asia, Africa, and other developing countries. Exploitation can occur at the community level as is sometimes seen throughout coastal villages of Southern Thailand where each resident may obtain for themselves every consumable of the mangrove forest (fuelwood, timber, honey, resins, crab, and shellfish) which then becomes threatened through increasing population and continual harvest. Other issues that occur on a global level include an uneven contribution to climate change, point and non-point pollution, and air and water quality issues due to destructive wetland practices.

Wetlands and climate change

Wetlands perform two important functions in relation to climate change. They have mitigation effects through their ability to sink carbon, and adaptation effects through their ability to store and regulate water.[47] Wetlands store approximately 44.6 Tg C y−1 globally.[48] In salt marshes and mangrove swamps in particular, the average carbon sequestration rate is 201 g CO2 m

−2 y−1 while peatlands sequester approximately 20-30g CO2 m−2 y−1.[48][49]



Carbon sequestration has sponsored blue carbon initiatives.More on blue carbon and carbon sequestration

They also are emitters of nitrous oxide, a major greenhouse gas.

Scientific projections

“Low water and occasional drying of the wetland bottom during droughts (dry marsh phase) stimulate plant recruitment from a diverse seed bank and increase productivity by mobilizing nutrients. In contrast, high water during deluges (lake marsh phase) causes turnover in plant populations and creates greater interspersion of element cover and open water, but lowers overall productivity. During a cover cycle that ranges from open water to complete vegetation cover, annual net primary productivity may vary 20-fold.”[50]

Nitrous oxide production from wetland soils

Coastal wetlands, such as tropical mangroves and temperate salt marshes are known to be sinks of carbon, therefore mitigating climate change, however they are also emitters of nitrous oxide (N2O),[51] which is a greenhouse gas with a global warming potential 300 times that of carbon dioxide and the dominant ozone depleting substance emitted in the 21st century.[52] Anthropogenic greenhouse gas (GHG) emissions have rapidly increased in the atmosphere due to the combustion of fossil fuels and deforestation practices, and these gases are major contributors to global climate change.

Although wetlands act as natural buffers towards nutrients expelled from surrounding watersheds, excess nutrients mainly through anthropogenic sources have been shown to significantly increase the N2O fluxes fluxes from their soils through denitrification and nitrification processes (Table 1).[53][54] Anthropogenic sources of nutrients into waterways have increased substantially causing eutrophication especially in coastal systems.[55][56] The main sources of coastal eutrophication are industrially made nitrogen, which is used as fertilizer in agricultural practices, as well as septic waste runoff.[57] Nitrogen (N) is the limiting nutrient for photosynthetic processes in saline systems, however in excess, it can lead to an overproduction of organic matter that then leads to hypoxic and anoxic zones within the water column.[58] Without oxygen, other organisms cannot survive, including economically important finfish and shellfish species. A study in the intertidal region of a New England salt marsh showed that excess levels of nutrients might increase N2O emissions rather than sequester them.[53]

Table 1. Nitrous oxide fluxes from different wetland soils. Table adapted from Moseman-Valtierra (2012)[59] and Chen et al. (2010) [60]

Wetland type Location N2O flux (µmol N2O m−2

h−1

)

Mangrove Shenzhen and Hong Kong 0.14-23.83 [60]

Mangrove Muthupet, South India 0.41-0.77 [61]

Mangrove Bhitarkanika, East India 0.20-4.73 [62]



Mangrove Pichavaram, South India 0.89-1.89 [62]

Mangrove Queensland, Australia -0.045-0.32 [63]

Mangrove South East Queensland, Australia 0.091-1.48 [64]

Mangrove Southwest coast, Puerto Rico 0.12-7.8 [65]

Mangrove Magueyes Island, Puerto Rico 0.05-1.4 [65]

Salt marsh Chesapeake Bay, USA 0.005-0.12 [66]

Salt marsh Maryland, USA 0.1 [67]

Salt marsh NE, China 0.1-0.16 [68]

Salt marsh Biebrza, Poland -0.07-0.06 [69]

Salt marsh Netherlands 0.82-1.64 [70]

Salt marsh Baltic sea -0.13 [71]

Salt marsh Massachusetts, USA -2.14-1.27 [72]

Nitrous oxide fluxes from wetlands in the southern hemisphere is lacking as are ecosystem based studies including the role of dominant organisms that alter sediment biogeochemistry. Aquatic invertebrates produce ecologically relevant nitrous oxide emissions emissions due to ingestion of denitrifying bacteria that live within the subtidal sediment and water column [73] and thus may also be influencing nitrous oxide production within wetlands.

Conservation

Main article: Wetland conservation

Wetlands have historically been the victim of large draining efforts for real estate development, or flooding for use as recreational lakes. Since the 1970s, more focus has been put on preserving wetlands for their natural function yet by 1993 half the world's wetlands had been drained.[74] Wetlands provide a valuable flood control function. Wetlands are very effective at filtering and cleaning water pollution,[75] (often from agricultural runoff from the farms that replaced the wetlands in the first place). To replace these wetland ecosystem services enormous amounts of money had to be spent on water purification plants, along with the remediation measures for controlling floods: dam and levee construction.

In order to produce sustainable wetlands, short-term, private-sector profits need to come secondary to global equity. Decision-makers must valuate wetland type, provided ecosystem service, long-term benefit, and current subsidies inflating valuation on either the private or public sector side. Analysis using the impact of hurricanes versus storm protection features projected wetland valuation at US$33,000/hectare/year.[76]



Balancing wetland conservation with the needs of people

Wetlands are vital ecosystems that provide livelihoods for the millions of people who live in and around them. The Millennium Development Goals (MDGs) called for different sectors to join forces to secure wetland environments in the context of sustainable development and improving human wellbeing. A three-year project carried out by Wetlands International in partnership with the International Water Management Institute found that it is possible to conserve wetlands while improving the livelihoods of people living among them. Case studies conducted in Malawi and Zambia looked at how dambos – wet, grassy valleys or depressions where water seeps to the surface – can be farmed sustainably to improve livelihoods. Mismanaged or overused dambos often become degraded, however, using a knowledge exchange between local farmers and environmental managers, a protocol was developed using soil and water management practices. Project outcomes included a high yield of crops, development of sustainable farming techniques, and adequate water management generating enough water for use as irrigation. Before the project, there were cases where people had died from starvation due to food shortages. By the end of it, many more people had access to enough water to grow vegetables. A key achievement was that villagers had secure food supplies during long, dry months. They also benefited in other ways: nutrition was improved by growing a wider range of crops, and villagers could also invest in health and education by selling produce and saving money.[77]

Ramsar Convention

Main article: Ramsar Convention

The Convention on Wetlands of International Importance, especially as Waterfowl Habitat, or Ramsar Convention, is an international treaty designed to address global concerns regarding wetland loss and degradation. The primary purposes of the treaty are to list wetlands of international importance and to promote their wise use, with the ultimate goal of preserving the world's wetlands. Methods include restricting access to the majority portion of wetland areas, as well as educating the public to combat the misconception that wetlands are wastelands. The Convention works closely with five International Organisation Partners. These are: Birdlife International, IUCN, International Water Management Institute, Wetlands International and World Wide Fund for Nature. The partners provide technical expertise, help conduct or facilitate field studies and provide financial support. The IOPs also participate regularly as observers in all meetings of the Conference of the Parties and the Standing Committee and as full members of the Scientific and Technical Review Panel.

Valuation

The value of a wetland system to the earth and to humankind is one of the most important valuations that can be computed for sustainable development. A guideline involving assessing a wetland, keeping inventories of known wetlands, and monitoring the same wetlands over time is the current process that is used to educate environmental decision-makers such as governments on the importance of wetland protection and conservation.

Important considerations



• Constructed Wetlands take 10–100 years to fully resemble the vegetative composition of a

natural wetland.

• Artificial wetlands do not have hydric soil. The soil has very low levels of organic carbon and

total nitrogen compared to natural wetland systems.

• Organic matter can be added to degraded natural wetlands to help restore their productivity

before the wetland is destroyed.[78]

Assessment

Rapid assessment.

Five steps to assessing a wetland

1. Collect general biodiversity data in order to inventory and prioritize wetland species,

communities and ecosystems. Obtain baseline biodiversity information for a given area.

2. Gather information on the status of a focus or target species such as threatened species.

Collect data pertaining to the conservation of a specific species.

3. Gain information on the effects of human or natural disturbance (changes) on a given area

or species.

4. Gather information that is indicative of the general ecosystem health or condition of a

specific wetland ecosystem.

5. Determine the potential for sustainable use of biological resources in a particular wetland

ecosystem.

Inventory

Developing a global inventory of wetlands has proven to be a large and difficult undertaking. Current efforts are based on available data, but both classification and spatial resolution have proven to be inadequate for regional or site-specific environmental management decision-making. It is difficult to identify small, long, and narrow wetlands within the landscape. Many of today’s remote sensing satellites do not have sufficient spatial and spectral resolution to monitor wetland conditions, although multispectral IKONOS and QuickBird data may offer improved spatial resolutions once it is 4 m or higher. Majority of the pixels are just mixtures of several plant species or vegetation types and are difficult to isolate which translates into an inability to classify the vegetation that defines the wetland. Improved remote sensing information, coupled with good knowledge domain on wetlands will facilitate expanded efforts in wetland monitoring and mapping. This will also be extremely important because we expect to see major shifts in species composition due to both anthropogenic land use and natural changes in the environment caused by climate change.

Monitoring

Mapping

A wetland system needs to be monitored over time to in order to assess whether it is functioning at an ecologically sustainable level or whether it is becoming degraded. Degraded wetlands will suffer a loss in water quality, a high number of threatened and endangered species, and poor soil conditions.



Due to the large size of wetlands, mapping is an effective tool to monitor wetlands. There are many remote sensing methods that can be used to map wetlands. Remote-sensing technology permits the acquisition of timely digital data on a repetitive basis. This repeat coverage allows wetlands, as well as the adjacent land-cover and land-use types, to be monitored seasonally and/or annually. Using digital data provides a standardized data-collection procedure and an opportunity for data integration within a geographic information system. Traditionally, Landsat 5 Thematic Mapper (TM), Landsat 7 Enhanced Thematic Mapper Plus (ETM + ), and the SPOT 4 and 5 satellite systems have been used for this purpose. More recently, however, multispectral IKONOS and QuickBird data, with spatial resolutions of 4 m by 4 m and 2.44 m by 2.44 m, respectively, have been shown to be excellent sources of data when mapping and monitoring smaller wetland habitats and vegetation communities.

For example, Detroit Lakes Wetland Management District assessed area wetlands in Michigan, USA using remote sensing. Through using this technology, satellite images were taken over a large geographic area and extended period. In addition, using this technique was less costly and time-consuming compared to the older method using visual interpretation of aerial photographs. In comparison, most aerial photographs also require experienced interpreters to extract information based on structure and texture while the interpretation of remote sensing data only requires analysis of one characteristic (spectral).

However, there are a number of limitations associated with this type of image acquisition. Analysis of wetlands has proved difficult because to obtain the data it is often linked to other purposes such as the analysis of land cover or land use. Practically, many natural wetlands are difficult to monitor as these areas are quite often difficult to access and require exposure to native wildlife and potential endemic disease.

Further improvements

Methods to develop a classification system for specific biota of interest could assist with technological advances that will allow for identification at a very high accuracy rate. The issue of the cost and expertise involved in remote sensing technology is still a factor hindering further advancements in image acquisition and data processing. Future improvements in current wetland vegetation mapping could include the use of more recent and better geospatial data when it is available.

List of wetland types

Wetland types:[79]

• A—Marine and Coastal Zone wetlands

1. Marine waters—permanent shallow waters less than six metres deep at low tide; includes

sea bays, straits

2. Subtidal aquatic beds; includes kelp beds, seagrasses, tropical marine meadows

3. Coral reefs

4. Rocky marine shores; includes rocky offshore islands, sea cliffs

5. Sand, shingle or pebble beaches; includes sand bars, spits, sandy islets

6. Intertidal mud, sand or salt flats

7. Intertidal marshes; includes saltmarshes, salt meadows, saltings, raised salt marshes, tidal

brackish and freshwater marshes



8. Intertidal forested wetlands; includes mangrove swamps, nipa swamps, tidal freshwater

swamp forests

9. Brackish to saline lagoons and marshes with one or more relatively narrow connections with

the sea

10. Freshwater lagoons and marshes in the coastal zone

11. Non-tidal freshwater forested wetlands

• B—Inland wetlands

1. Permanent rivers and streams; includes waterfalls

2. Seasonal and irregular rivers and streams

3. Inland deltas (permanent)

4. Riverine floodplains; includes river flats, flooded river basins, seasonally flooded grassland,

savanna and palm savanna

5. Permanent freshwater lakes (> 8 ha); includes large oxbow lakes

6. Seasonal/intermittent freshwater lakes (> 8 ha), floodplain lakes

7. Permanent saline/brackish lakes

8. Seasonal/intermittent saline lakes

9. Permanent freshwater ponds (< 8 ha), marshes and swamps on inorganic soils; with

emergent vegetation waterlogged for at least most of the growing season

10. Seasonal/intermittent freshwater ponds and marshes on inorganic soils; includes sloughs,

potholes; seasonally flooded meadows, sedge marshes

11. Permanent saline/brackish marshes

12. Seasonal saline marshes

13. Shrub swamps; shrub-dominated freshwater marsh, shrub carr, alder thicket on inorganic

soils

14. Freshwater swamp forest; seasonally flooded forest, wooded swamps; on inorganic soils

15. Peatlands; forest, shrub or open bogs

16. Alpine and tundra wetlands; includes alpine meadows, tundra pools, temporary waters from

snow melt

17. Freshwater springs, oases and rock pools

18. Geothermal wetlands

19. Inland, subterranean karst wetlands

• C—Human-made wetlands

1. Water storage areas; reservoirs, barrages, hydro-electric dams, impoundments (generally > 8

ha)

2. Ponds, including farm ponds, stock ponds, small tanks (generally < 8 ha)

3. Aquaculture ponds; fish ponds, shrimp ponds

4. Salt exploitation; salt pans, salines

5. Excavations; gravel pits, borrow pits, mining pools

6. Wastewater treatment; sewage farms, settling ponds, oxidation basins

7. Irrigated land and irrigation channels; rice fields, canals, ditches

8. Seasonally flooded arable land, farm land



Lagoon From Wikipedia, the free encyclopedia

This article is about the geographical feature. For other uses of lagoon, see Lagoon (disambiguation).

A lagoon is a shallow body of water separated from a larger body of water by barrier islands or reefs. Lagoons

are commoDefinition

Garabogaz-Göl lagoon in Turkmenistan

Lagoons are shallow, often elongated bodies of water separated from a larger body of water by a shallow or exposed shoal, coral reef, or similar feature. Some authorities (such as Nybakken[who?]) include fresh water bodies in the definition of "lagoon", while others explicitly restrict "lagoon" to bodies of water with some degree of salinity. The distinction between "lagoon" and "estuary" also varies between authorities. Richard A. Davis Jr. restricts "lagoon" to bodies of water with little or no fresh water inflow, and little or no tidal flow, and calls any bay that receives a regular flow of fresh water an "estuary". Davis does state that the terms "lagoon" and "estuary" are "often loosely applied, even in scientific literature."[1] Kusky[who?] characterizes lagoons as normally being elongated parallel to the coast, while estuaries are usually drowned river valleys, elongated perpendicular to the coast.[1][2][3][4][5] When used within the context of a distinctive portion of coral reef ecosystems, the term "lagoon" is synonymous with the term "back reef" or "backreef", which is more commonly used by coral reef scientists to refer to the same area.[6] Coastal lagoons are classified as inland bodies of water.[7][8]

Many lagoons do not include "lagoon" in their common names. Albemarle and Pamlico sounds in North Carolina,[9] Great South Bay between Long Island and the barrier beaches of Fire Island in New York,[10] Isle of Wight Bay, which separates Ocean City, Maryland from the rest of Worcester County, Maryland,[11] Banana River in Florida,[12] Lake Illawarra in New South Wales,[13] Montrose Basin in Scotland,[14] and Broad Water in Wales have all been classified as lagoons, despite their names. In England, The Fleet at Chesil Beach has also been described as a lagoon.



In Latin America, the term “laguna”, which lagoon translates to, is often used to describe a lake, such as Laguna Catemaco. In Portuguese, “lagoa” may be a body of shallow sea water, but also a relatively small freshwater lake not linked to the sea.

Etymology

"Lagoon" is derived from the Italian laguna, which refers to the waters around Venice, the Lagoon of Venice. Laguna is attested in English by at least 1612, and had been Anglicized to "lagune" by 1673. In 1697 William Dampier referred to a "Lagune or Lake of Salt water" on the coast of Mexico. Captain James Cook described an island "of Oval form with a Lagoon in the middle" in 1769.[15]

Atoll lagoons

Atoll lagoons form as coral reefs grow upwards while the islands that the reefs surround subside, until eventually only the reefs remain above sea level. Unlike the lagoons that form shoreward of fringing reefs, atoll lagoons often contain some deep (>20m) portions.

Coastal lagoons

Coastal lagoon landscapes around the island of Hiddensee near Stralsund, Germany. Many similar coastal lagoons can be found around the Western Pomerania Lagoon Area National Park.

Coastal lagoons form along gently sloping coasts where barrier islands or reefs can develop off-shore, and the sea-level is rising relative to the land along the shore (either because of an intrinsic rise in sea-level, or subsidence of the land along the coast). Coastal lagoons do not form along steep or rocky coasts, or if the range of tides is more than 4 metres (13 ft). Due to the gentle slope of the coast, coastal lagoons are shallow. They are sensitive to changes in sea level due to global warming. A relative drop in sea level may leave a lagoon largely dry, while a rise in sea level may let the sea breach or destroy barrier islands, and leave reefs too deep under water to protect the lagoon. Nybakken describes coastal lagoons and barrier islands as a "coupled system". Coastal lagoons are young and dynamic, and may be short-lived in geological terms. Coastal lagoons are common, occurring along nearly 15 percent of the world's shorelines. In the United States, lagoons are found along more than 75 percent of the eastern and Gulf coasts.[3][4]

Coastal lagoons are usually connected to the open ocean by inlets between barrier islands. The number and size of the inlets, precipitation, evaporation, and inflow of fresh water all affect the nature of the lagoon. Lagoons with little or no interchange with the open ocean, little or no inflow of fresh water, and high evaporation rates, such as Lake St. Lucia, in South Africa, may become highly saline. Lagoons with no connection to the open ocean and



significant inflow of fresh water, such as the Lake Worth Lagoon in Florida in the middle of the 19th century, may be entirely fresh. On the other hand, lagoons with many wide inlets, such as the Wadden Sea, have strong tidal currents and mixing. Coastal lagoons tend to accumulate sediments from inflowing rivers, from runoff from the shores of the lagoon, and from sediment carried into the lagoon through inlets by the tide. Large quantities of sediment may be occasionally be deposited in a lagoon when storm waves overwash barrier islands. Mangroves and marsh plants can facilitate the accumulation of sediment in a lagoon. Benthic organisms may stabilize or destabilize sediments.[3][4]

River-mouth lagoons on mixed sand and gravel beaches

River-mouth lagoons on mixed sand and gravel (MSG) beaches form at the river-coast interface where a typically braided, although sometimes meandering, river interacts with a coastal environment that is significantly affected by longshore drift.[16] The lagoons which form on the MSG coastlines are common on the east coast of the South Island, New Zealand and have long been referred to as hapua by the Māori. This classification differentiates hapua from similar lagoons located on the New Zealand coast termed waituna. Hapua are often located on paraglacial coastal areas[17] where there is a low level of coastal development and minimal population density. Hapua form as the river carves out an elongated coast-parallel area, blocked from the sea by a MSG barrier which constantly alters its shape and volume due to longshore drift.[16][18] Longshore drift continually extends the barrier behind which the hapua forms by transporting sediment along the coast. Hapua are defined as a narrow shore-parallel extensions of the coastal riverbed.[18] They discharge the majority of stored water to the ocean via an ephemeral and highly mobile drainage channel or outlet.[19] The remainder percolates through the MSG barrier due to its high levels of permeability. Hapua systems are driven by a wide range of dynamic processes that are generally classified as fluvial or marine; changes in the balance between these processes as well as the antecedent barrier conditions can cause shifts in the morphology of the hapua, in particular the barrier. New Zealand examples include the Rakaia, Ashburton and Hurunui river-mouths.

Hapua environment

Hapua have been identified as establishing in the Canterbury Bight coastal region on the east coast of the South Island. They are often found in areas of coarse-grained sediment where contributing rivers have moderately steep bed gradients.[16] MSG beaches in the Canterbury Bight region contain a wide range of sediment sizes from sand to boulders[20] and are exposed to the high energy waves that make up an east coast swell environment.[21] MSG beaches are reflective rather than dissipative energy zones due to their morphological characteristics. They have a steep foreshore which is known as the ‘engine room’ of the beach profile. In this zone, swash and backwash are dominating processes alongside longshore transport.[22] MSG beaches do not have a surf zone; instead a single line of breakers is visible in all sea conditions.[16] Hapua are associated with MSG beaches as the variation in sediment size allows for the barrier to be permeable.

The east coast of the South Island has been identified as being in a period of chronic erosion of approximately 0.5 metres per year.[23] This erosion trend is a result of a number of factors. According to the classification scheme of Zenkovich,[17] the rivers on the east coast can be described as ‘small’; this classification is not related to their flow rate but to the insufficient amount of sediment that they transport to the coast to nourish it. The sediment provided is not



adequate to nourish the coast against its typical high energy waves and strong longshore drift. These two processes constantly remove sediment depositing it either offshore or further up drift.[24] As the coastline becomes eroded the hapua have been 'rolling back' by eroding the backshore to move landwards.[18]

Hapua or river-mouth lagoons form in micro-tidal environments. A micro-tidal environment is where the tidal range (distance between low tide and high tide) is less than two metres.[16] Tidal currents in a micro-tidal zone are less than those found on meso-tidal (two – four metres) and macro-tidal (greater than four metres) coastlines.[25] Hapua form in this type of tidal environment as the tidal currents are unable to compete with the powerful freshwater flows of the rivers therefore there is no negligible tidal penetration to the lagoon.[16] A fourth element of the environment in which hapua form is the strong longshore drift component.[16] Longshore or littoral drift is the transportation of sediments along the coast at an angle to the shoreline. In the Canterbury Bight coastal area; the dominant swell direction is northwards from the Southern Ocean.[16] Therefore the principal movement of sediment via longshore drift is north towards Banks Peninsula. Hapua are located in areas dominated by longshore drift; because it aids the formation of the barrier behind which the hapua is sited.

A hapua also requires sediment to form the lagoon barrier. Sediment which nourishes the east coast of New Zealand can be sourced from three different areas. Material from the highly erodible Southern Alps is removed via weathering; then carried across the Canterbury Plains by various braided rivers to the east coast beaches.[18][24] The second source of sediment is the high cliffs which are located in the hinterland of lagoons.[24] These can be eroded during the occurrence of high river flow or sea storm events. Beaches further south provide nourishment to the northern coast via longshore transport.

Hapua characteristics

Hapua have a number of characteristics which includes shifts between a variety of morphodynamic states due to changes in the balance between marine and fluvial processes as well as the antecedent barrier conditions.[18] The MSG barrier constantly changes size and shape as a result of the longshore drift. Water stored in the hapua drains to the coast predominately though an outlet; although it can also seep through the barrier depending on the permeability of the material.[18][26]

Changes in the level of the lagoon water do not occur as a result of saltwater or tidal intrusion. Water in a hapua is predominately freshwater originating from the associated river. Hapua are non-estuarine, there is no tidal inflow however the tide does have an effect on the level of water in the lagoon. As the tide reaches its peak, the lagoon water has a much smaller amount of barrier to permeate through so the lagoon level rises.[27] This is related to a physics theory known as hydraulic head. The lagoon level has a similar sinusoidal wave shape as the tide but reaches its peak slightly later.[26] In general, any saltwater intrusion into the hapua will only occur during a storm via wave overtopping or sea spray.[18][24]

Hapua can act as both a source and sink of sediment.[23][24] The majority of sediment in the hapua is fluvial sourced.[16] During medium to low river flows, coarser sediment generally collects in the hapua; while some of the finer sediment can be transported through the outlet to the coast.[24] During flood events the hapua is 'flushed out' with larger amounts of sediment transferred through the outlet. This sediment can be deposited offshore or downdrift of the hapua replenishing the undernourished beach.[24] If a large amount of material is released to



the coast at one time it can be identified as a 'slug'. These can often be visible from aerial photographs.

Antecedent barrier conditions combined with changes in the balance between marine and fluvial processes results in shifts between a variety of morphological states in a hapua or river-mouth lagoon on a MSG beach. Marine processes includes the direction of wave approach, wave height and the coincidence of storm waves with high tides.[28] Marine processes tend to dominate the majority of morphodynamic conditions until there is a large enough flood event in the associated river to breach the barrier.[16] The level and frequency of base or flood flows are attributed to fluvial processes. Antecedent barrier conditions are the permeability, volume and height of the barrier as well as the width and presence of previous outlet channels.[28] During low to medium river flows, the outlet from the lagoon to the sea becomes offset in the direction of longshore drift.[24] Outlet efficiency tends to decrease the further away from the main river-mouth the outlet is.[18] A decrease in efficiency can cause the outlet to become choked with sediment and the hapua to close temporarily. The potential for closure varies between different hapua depending on whether marine or fluvial processes are the bigger driver in the event. A high flow event; such as a fresh or flood can breach the barrier directly opposite the main river channel.[18][24] This causes an immediate decrease in the water level of the hapua; as well as transporting previously deposited sediments into the ocean. Flood events are important for eroding lagoon back shores; this is a behaviour which allows hapua to retreat landward and thus remain coastal landforms even with coastal transgression and sea level rise.[18] During high flow events there is also the possibility for secondary breaches of the barrier or lagoon truncation to occur.

Storm events also have the ability to close hapua outlets as waves overtop the barrier depositing sediment and choking the scoured channel.[23] The resultant swift increase in lagoon water level causes a new outlet to be breached rapidly due to the large hydraulic head that forms between the lagoon and sea water levels. Storm breaching is believed to be an important but unpredictable control on the duration of closures at low to moderate river flow levels in smaller hapua.[23]

Hapua are extremely important for a number of reasons. They provide a link between the river and sea for migrating fish as well as a corridor for migratory birds.[16][29] To lose this link via closure of the hapua outlet could result in losing entire generations of specific species as they may need to migrate to the ocean or the river as a vital part of their lifecycle. River-mouth lagoons such as hapua were also used a source for mahinga kai (food gathering) by the Māori people.[16][29] However, this is no longer the case due to catchment degradation which has resulted in lagoon deterioration. River-mouth lagoons on MSG beaches are not well explained in international literature.

Hapua case study



Aerial photograph of the Rakaia river-mouth and associated hapua

The hapua located at the mouth of the Rakaia River stretches approximately three kilometres north from where the river-mouth reaches the coast. The average width of the hapua between 1952 and 2004 was approximately 50 metres; whilst the surface area has stabilised at approximately 600,000 square metres since 1966.[30] The coastal hinterland is composed of erodible cliffs and a low lying area commonly known as the Rakaia Huts. This area has changed notably since European Settlement; with the drainage of ecologically significant wetlands and development of the small bach community.

The Rakaia River begins in the Southern Alps, providing approximately 4.2 Mt per year of sediment to the east coast. It is a braided river with a catchment area of 3105 kilometres squared and a mean flow of 221 cubic metres per second.[31] The mouth of the Rakaia River reaches the coast south of Banks Peninsula. As the river reaches the coast it diverges into two channels; with the main channel flowing to the south of the island.[23] As the hapua is located in the Canterbury Bight it is in a state of constant morphological change due to the prevailing southerly sea swells and resultant northwards longshore drift.

Images

Lagoon

Glenrock Lagoon in Australia



Lagoa dos Patos lagoon in Brazil

Apoyo Lagoon Natural Reserve in Nicaragua

Venetian Lagoon as seen by Landsat 1, Veneto (Northeast Italy)





Szczecin Lagoon as seen by Landsat c. 2000.

Vistula and Curonian lagoons on the Baltic Sea.

Nearly half the area of Kiritimati is covered with lagoons, some freshwater and some seawater.



Blue lagoon, Ölüdeniz, Turkey

Washdyke Lagoon in New Zealand

Araruama Lagoon is a lagoon next to the shore of Rio de Janeiro State, is the largest hypersaline lagoon in the world.

Marine and Coastal Living Resources Marine and coastal living resources make up one of the programme elements of the elaborated

programme of work on marine and coastal biological diversity, adopted at the seventh meeting of

the Conference of the Parties and contained in the annex to decision VII/5.



The overall goal of this programme element is to achieve conservation and long-term sustainable

use of marine and coastal living resources in a manner that respects both societal interests and the

integrity of ecosystems. Deep seabed biodiversity and coral are two focal areas of this programme

element.

Many of the world's fishery resources are in danger of depletion. In addition, other living resources,

such as mangroves, coral species and species amenable to bioprospecting, are subject to or under

threat of overexploitation. The principal impact of overexploitation is unsustainable removal of

marine and coastal living resources. The significant threats to biological diversity include habitat

destruction, destructive fishing and Illegal, Unregulated and Unreported (IUU) fishing, and by-catch.

The increasing number and severity of coral bleaching events induced by climate change is also a

cause of concern to the Parties to the Convention. As a result, the Conference of the Parties updated

the specific work plan on coral bleaching in decision VII/5 with the aim to make it increasingly action-

oriented in undertaking management actions and strategies to support reef resilience, rehabilitation

and recovery. The amendments to the coral bleaching work plan recognize the need to manage coral

reefs for resistance and resilience to, and recovery from, episodes of raised sea temperatures and/or

coral bleaching, including taking such factors into account when designing networks of marine

protected areas (MPAs).

The Parties to the Convention on Biological Diversity have also expressed their concerns about the

increased risks to biodiversity in marine waters beyond the limits of national jurisdiction. This

concern is expressed in decision VII/5, where the COP underlined that there is an urgent need for

international cooperation and action to improve conservation and sustainable use of biodiversity in

marine areas beyond the limits of national jurisdiction, including through the establishment of

marine protected areas consistent with international law and based on scientific information. In this

regard, seamounts, hydrothermal vents, cold-water corals and other vulnerable ecosystems were

identified in paragraph 59 of decision VII/5 as threatened areas in need of rapid action to address

threats by increasing human activities in the context of the precautionary approach and the

ecosystem approach.

The COP recognized that MPAs represent only one of the many available tools for conservation and

sustainable use of biodiversity in marine areas beyond national jurisdiction, and that other means

for preventing practices destructive to biodiversity also exist. With this in mind, the COP, in

paragraph 61, called upon the United Nations General Assembly and other relevant international

and regional organizations, within their mandate, according to their rules of procedure, to urgently

take the necessary short-term, medium-term and long-term measures to eliminate/avoid

destructive practices, consistent with international law, on scientific bases, including the application

of precaution, for example, consideration on a case-by-case basis, of interim prohibition of

destructive practices adversely impacting the marine biological diversity associated in particular with

areas with seamounts, hydrothermal vents, cold-water corals, other vulnerable ecosystems and

certain other underwater features.

The ecosystem approach remains the basis for the Convention’s approach to the management of living resources. According to decision II/10, as adopted by the Conference of the Parties

at its second meeting in Jakarta in November 1995, the present mono-species approach to modeling and assessment should be augmented by an ecosystem process-oriented approach,



based on research of ecosystem processes and functions, with an emphasis on identifying ecologically critical processes that consider the spatial dimension of these processes. Models

of ecosystem processes should be developed through trans-disciplinary scientific groups, including ecologists, oceanographers, economists, and fisheries experts, and be applied to the management of sustainable marine and coastal resources and environment. The central role of

the ecosystem approach is also echoed in decisionCoastal

Processes and Features

Discussion

To understand a coastal system and how it functions, it is essential that you know how the primary features of the coastal system formed. Understanding how coastal processes lead to the development of certain coastal features is not only interesting but critical to enabling you to predict what will happen in the near future in a particular coastal zone. This is the foundation of sound coastal planning for long-term human development and coexistence within the coastal environment. Furthermore, once you have a solid grasp of the cause-and-effect relationships at work in a coastal system, you can go to any coastal area and quickly discern the dominant processes at play by recognizing features covered in this chapter, and associating them with their related processes.

Dominant Coastal Processes

In a coastal environment, land affects the ocean, and the ocean influences the terrestrial environment. Therefore, coastal ocean processes and land are interactive with each other. Listed and described below are the dominant processes at work in a coastal environment.

A. An ocean current is a coherent flow of water molecules generally moving in the same direction. Coastal-ocean currents transport nutrients, energy, and sediment as they flow.

1. large-scale nearshore and offshore currents - generally flow parallel to the coast; flow is typically related to gyre current flow, or possibly to seasonal wind flow. An example is the California Current which flows equatorward along the coast of Oregon and California. Velocity of the California Current increases during winter and spring as south-flowing winds add energy to its flow. These large-scale currents play a critical role in distributing nutrients and plankton within the surface zone of a coastal ocean.

2. longshore current - flows parallel to the coast, but only within the surf zone (between breaking waves and the shoreline). Longshore current, formed as waves



break and release energy at an angle to the shoreline, are significant because they can transport great quantities of sediment from where it is introduced into the ocean by a stream to beaches up or down the coast. Observe the wave washing ashore at Huntington Beach, at the lower left. As it breaks and releases energy, the resulting longshore current will flow toward the lower left corner of the photograph.

3. rip current - (formerly and incorrectly referred to as "rip tide") flows offshore from shallow surf-zone water. Rips form where longshore currents or wave backwash collide due to the configuration of the coastal or beach topography. A strong rip current can carry sediment and swimmers out past the breaker zone. Shown below are rip currents along Peninsula Beach, Long Beach, California. Note the plumes of sediment carried offshore by the rip currents, which are more visible in the second photograph.





4. tidal current - forms within restricted inlets to bays and harbors as tide rises, forming a flood current, or as tide lowers, forming an ebb current. Tidal currents are often the sole means for circulating water within bays and harbors.

5. upwelling current - the movement of deep, cold, nutrient-rich water up towards the surface, enabled by the horizontal movement of surface ocean water. Upwelling occurs where surface coastal-ocean water is forced away from shore by an offshore wind, or by the Coriolis effect causing a nearshore current to veer offshore.

B. Ocean waves are nearly friction-free wave-form energy capable of traveling great distances within the surface zone of the ocean. Most waves form as wind transfers energy into the water. A wave's energy is is typically released within the surf zone as they begin to "feel bottom", slow dramatically, and then break. (Energy may be released further inland due to a combination of large storm waves and high tide, or due to a tsunami.)

1. swell - waves of fairly equal height, length, and period which form as storm-generated waves become sorted according to size and period as they move away from the storm's center. Swell, in the photograph of the Oceanside, California coast, can travel thousands of miles before breaking along a distant shore.



2. local wind waves - generally smaller and less organized than swell, local wind waves can be superimposed onto swell, making the ocean surface chaotic. Surfers dislike these smaller waves, referring to them as "wind chop", because they mess up the uniform swell waves. The photograph below shows Long Beach Harbor on a breezy day, with small locally formed wind waves, and no ocean swell.

3. wave interference - the interactions of two sets of swell can result in waves much smaller than usual (destructive interference) or much larger than usual (constructive interference). (The latter possibility can form dangerous rogue waves on the open ocean, or so-called "creeper waves" along a beach.) Wave interference can also occur where an incoming wave reflects off of a jetty. The reflected wave can then interfere with the next incoming wave to form a peaked wave of great height, such as the Wedge at Newport Beach shown below.





4. wave refraction - occurs as as a portion of an incoming wave begins to interact with the ocean floor, slowing some of the wave and bending it in one direction or another. This can focus a wave's energy on a submerged reef, forming an excellent surf locale such as Jaws off the coast of Maui, Hawaii. More typically, the wave's energy is focused on a small rocky island (stack) or a headland that juts out into the ocean. This photograph shows the refraction of waves as they enter Bluff Cove along the shore of Palos Verdes Peninsula, California.

5. wave diffraction - an obstacle (island or breakwater) forms a new point of departure for a wave, spreading the wave's energy over a greater area. This occurs because the obstacle creates a wave-shadow zone behind it, with propagating waves spreading laterally with diminished size and energy. This process is significant for waves moving through the Southern California Bight, as illustrated by the wave shadows created by the Channel Islands in the Scripps coastal data diagram below.



C. Given time, a shoreline with multiple embayments and headlands will become fairly straight. This long-term process requires a combination of ocean current and wave action, which erodes headlands and fills in embayments with sediment. For shoreline straightening to transpire, tectonic uplift must be absent.

Coastal Features

Generally speaking, coastal features are classified according to the dominant processes at work along a coast - either erosional or depositional.

A. Depositional coastal features require an abundance of sediment, and adequate energy to move the sediment around within the ocean. Listed and described below are some common coastal features formed as sediment settles from coastal currents and waves.

1. beach - is usually composed of sand-sized sediment which is deposited a short distance inland as well as offshore. Beaches are formed by a combination of



longshore current, which transports sediment parallel to shore within the surf zone, and wave action which bulldozes the sediment shoreward. Capistrano Beach, California, shown below, receives sediment carried from San Juan Creek by longshore current. "Capo" Beach is notorious for its rip currents, indicated by the plumes of sediment in the photograph.

2. spit - an elongate buildup of sediment that develops as a strong longshore current carries sand and silt out across a harbor or bay entrance, or from a point of land. The spit that exists near the entrance of Santa Barbara Harbor, shown below, is constantly dredged away to keep the harbor entrance open.



3. barrier island - a low-lying, elongate sandy island separating the open ocean from a shallow lagoon and mainland. A barrier island can form where a vast amount of sediment is piled onto a shallow continental shelf by small waves, or where coastal dunes became flooded due to a rise in ocean level since the last ice age approximately 19,000 years ago. In the Southern California Bight, there were barrier islands where Los Angeles/Long Beach Harbor now exists. The largest of the barrier islands was called Rattlesnake Island, shown below. Part of Rattlesnake Island still exists, as Terminal Island.





4. delta - a large fan-shaped wedge of sediment formed where a sediment-laden stream enters the ocean. Some large deltas, such as the Mississippi River delta, support vast wetland habitats as well as agriculture and mariculture. Southern California deltas are transient features which tend to form and grow during times of prolonged rainfall, which triggers high-volume stream flow capable of transporting lots of sediment to the ocean. Otherwise, moderate to occaisional heavy surf can wear away the deltas, such as the Malibu Creek delta shown below.

5. coastal plain - the relatively flat land adjacent to a shoreline. Coastal plains usually form as streams spread sediment over a large floodplain area during a period of thousands of years. The Los Angeles coastal plain is the largest in southern California, but there are many others like the Santa Barbara coastal cell shown below.



6. continental shelf - the generally flat and shallow ocean bottom extending from the shoreline out to the continental slope, where depth increases rapidly. The shelf itself is mostly composed of terrigenous (land-derived) sediment deposited on the submerged edge of a continent, along with some biogenous skeletal sediment produced as marine organisms die in shelf water. Note that shelves along tectonically active coasts tend to be narrow (<50 miles across) whereas shelves along passive coastal margins tend to be wider (>50 miles across). On the topographic/bathymetric map below, the widest shelf is 16 miles across, and the narrowest is three miles across. This map was produced by SCCOOS (Southern California Coastal Ocean Observing System). The transition from the shelf edge down to the basin floor is referred to as the continental slope.



B. Erosional coastal features are formed by the combination of terrestrial processes (weathering, stream flow, and mass wasting) and marine processes (waves and currents). Tectonic uplift can rejuvenate some of these features.

1. headland - a portion of an elevated coastal landscape that juts out into the ocean. Formation of a headland can involve several processes, including erosion by streams, unequal weathering of coastal cliffs, wave action, and movement of rocks along a fault. Some headlands are products of only one or two of these processes, whereas others are affected by all of the processes to varying degrees. Point Dume, near Malibu, is a product of several of these headland-forming processes.



2. coastal cliff - forms where wave erosion over-steepens an elevated coastline. This leads to mass wasting in the form of rock falls and slides, which cause the cliff to retreat from the ocean. Homes built close to the edge of a coastal cliffs can be destroyed if this process occurs rapidly due to a major storm and large waves, combined with high tide which allows the waves to pound directly into the base of coastal cliffs. The photographs below shows the remnants of a San Pedro, California neighborhood that was abandoned in the 1940's due to wave erosion and mass wasting of coastal cliffs. For obvious reasons, the area is referred to by locals as "Sunken City".





How would you describe the state of equilibrium of the Sunken City coast line? (Remember the terms steady-state, meta-stable and dynamic equilibrium?) Is

positive or negative feedback at work here?

3. wave-cut platform - fairly flat intertidal portion of a rocky shoreline at the base of coastal cliffs, formed by a combination of wave abrasion (energetic movement of sediment grains against rocks), wave force (pounding action and compression of air into rock fractures), and biological activity (boring organisms). When exposed by low tide, platforms hold tide pools, an extreme environment requiring specialized survival adaptations by tide-pool organisms. Portuguese Point and Inspiration Point, on Palos Verdes Peninsula, both have well-developed wave-cut platforms visible in the photograph below.

Note that uplifted platforms form wave-cut terraces, highly valued coastal landforms that offer flat terrain and beautiful vistas of the coastal environment. Palos Verdes Peninsula, southern California has a total of 13 wave-cut platforms, representing progressive tectonic uplift over the past several million years. The youngest, terrace 13, is closest to ocean level.



Below is a view of terraces 12 and 13, from terrace 11, Palos Verdes Peninsula.



4. submarine canyon - an incision cut into a continental shelf and slope. Initially the erosion was by a stream flowing across a continental shelf exposed during a lowstand/regression of the ocean associated with past ice age/global-cooling events. Later, global warming would lead to a highstand/transgression of the ocean, flooding the shelf and stream valley. Coastal-ocean turbulence due to storm activity can mix sediment with water, forming a water mass denser than surrounding water. Gravity pulls this dense water downward through the already-existing valley, forming turbidity currents capable of scouring the valley into a deep, long submarine canyon. Worldwide there are over 100 submarine canyons along continental margins, with six just off the coast of southern California. The multi-beam radar topographic/bathymetric map below shows the prominent features of coastal Los Angeles and vicinity. Most obvious are the deep basins off shore, and the continental shelf. The best-developed submarine canyon in this view is the Redondo Submarine Canyon (RSC), probably formed in conjunction with the Los Angeles River and past global-cooling events.



Coastal Processes

The coastal zone is that part of the land surface influenced by marine processes. It extends from the landward limit of tides, waves, and wind blown coastal dunes, and seaward to the point at which waves interact significantly with the seabed.The coastal zone is a dynamic part of the Earth's surface where both marine and atmospheric processes produce rocky coasts, as well as beaches and dunes, barriers and tidal inlets, and shape deltas. The atmospheric processes include temperature, precipitation, and winds, while the major marine processes are waves and tides, together with water temperature and salinity. The coast also supports rich ecosystems, including salt marshes, mangroves, seagrass, and coral reefs. The diverse coastal ecology is favored by the shallow waters, abundant sunlight, terrestrial and marine nutrients, tidal and wave flushing, and a range of habitat types.

Waves — generation and types.

Waves provide about half the energy to do work at the coast. Ocean waves are generated by wind blowing over the ocean surface. The stronger the wind, the longer it blows and the longer the fetch, or stretch of ocean over which it blows, the larger the waves (Figure 1). The world's greatest wave factories are in the zone of sub-polar lows centered on 40–60° N and S latitudes, the so-called roaring 40's and screaming 60's. The strong westerly winds produce the world's biggest waves which initially head west, and are deflected equatorward by the Coriolis effect, arriving from the northwest in the northern hemisphere and southwest in the southern hemisphere (Figure 2). Other major wave climates are the easterly waves produced by the expansive but moderate velocity northeast and southeast Trade winds — and lesser



seasonal waves produced by the monsoons and even the polar easterlies, togetoccasional hurricanes that can produce massive waves as well as storm surges.

Figure 1 As wind velocity increases, the period or time between waves, and wave length, increases, and the amount of energy transferred to the waves increases exponentvelocity doubles from 37 to 75 km/hr the amount of energy increases exponentially. Very strong winds are therefore required to generate the biggest waves.© 2012 Nature Education All rights reserved.



seasonal waves produced by the monsoons and even the polar easterlies, togetoccasional hurricanes that can produce massive waves as well as storm surges.

As wind velocity increases, the period or time between waves, and wave length, increases, and the amount of energy transferred to the waves increases exponentially. Note how as wind velocity doubles from 37 to 75 km/hr the amount of energy increases exponentially. Very strong winds are therefore required to generate the biggest waves.

All rights reserved.

seasonal waves produced by the monsoons and even the polar easterlies, together with occasional hurricanes that can produce massive waves as well as storm surges.

As wind velocity increases, the period or time between waves, and wave length, increases, ially. Note how as wind

velocity doubles from 37 to 75 km/hr the amount of energy increases exponentially. Very





Figure 2 The highest waves occur in the Southern Ocean and north Pacific and Atlantic where they are generated by strong sub-polar lows. They average 5Southern Ocean has the most pers(centre), and at least 2–3 m 90% of the year (bottom). While the subblow year round across huge sections of ocean, they are of only moderate velocity, and hence generate only moderate waves.© 2012 Nature Education Reprinted with permission from Short & Woodroffe 2009. All rights reserved.

When waves are being generated they are called a slower waves, which tend to topple over and break, and have a broad spectrum of direction. Once the wind stops blowing, and/or the waves leave the area of generation, they quickly transform into swell — lower, longer, faster and uniform in directiontheoretically travel around the world with minimal loss of energy, while in reality they eventually break on some distant shore.

Waves are a form of potential energy that can be transported across hundreds to thousands of kilometers of ocean to be released as kinetic energy when they shoal and break. Waves are defined by their height (H) (trough to crest), between successive crests). The longer the period the longer and faster the waves, as length L=1.56 T, and wave velocityvelocity is controlled by the water depth (d) such that C=constant. For this reason waves slow down as they move towards the shore, with a 10 sec wave traveling at 56 km/hr (35 mph) in deep water slowdepth.

Tides and tidal currents.

Tides are produced by the gravitational pull of the Moon and Sun acting on a rotating Earth. This pull produces a very slight bulge in the ocean, which we know as tide. The tides and the currents they generate are responsible for about 50% of the marine energy delivered to the coast. The major impact of tides is to shift the shoreline between high and low tide, and to generate tidal currents either parallel to the coast, or at tidal inletsflowing into the inlets and perpendicular to the coast (Figure 3).



The highest waves occur in the Southern Ocean and north Pacific and Atlantic where they are polar lows. They average 5–6 m in height 10% of the year (top). The

Southern Ocean has the most persistent higher waves averaging 3–4 m 50% of the time 3 m 90% of the year (bottom). While the sub-tropical trade winds also

blow year round across huge sections of ocean, they are of only moderate velocity, and hence derate waves.

Reprinted with permission from Short & Woodroffe 2009. All

When waves are being generated they are called a sea and consist of short, steep,slower waves, which tend to topple over and break, and have a broad spectrum of direction. Once the wind stops blowing, and/or the waves leave the area of generation, they quickly

lower, longer, faster and uniform in direction. Swell waves can theoretically travel around the world with minimal loss of energy, while in reality they eventually break on some distant shore.

Waves are a form of potential energy that can be transported across hundreds to thousands of ean to be released as kinetic energy when they shoal and break. Waves are

(H) (trough to crest), length (L) (crest to crest) and between successive crests). The longer the period the longer and faster the waves, as

wave velocity C = 1.56 T2. When waves enter shallow water their velocity is controlled by the water depth (d) such that C=√gd where g is the gravitational constant. For this reason waves slow down as they move towards the shore, with a 10 sec wave traveling at 56 km/hr (35 mph) in deep water slowed to 7 km/hr (4 mph) in 5 m water

Tides and tidal currents.

are produced by the gravitational pull of the Moon and Sun acting on a rotating Earth. This pull produces a very slight bulge in the ocean, which we know as tide. The tides and the currents they generate are responsible for about 50% of the marine energy delivered to the coast. The major impact of tides is to shift the shoreline between high and low tide, and to generate tidal currents either parallel to the coast, or at tidal inlets and estuaries, currents flowing into the inlets and perpendicular to the coast (Figure 3).

The highest waves occur in the Southern Ocean and north Pacific and Atlantic where they are 6 m in height 10% of the year (top). The

4 m 50% of the time tropical trade winds also

blow year round across huge sections of ocean, they are of only moderate velocity, and hence


and consist of short, steep, high, slower waves, which tend to topple over and break, and have a broad spectrum of direction. Once the wind stops blowing, and/or the waves leave the area of generation, they quickly

. Swell waves can theoretically travel around the world with minimal loss of energy, while in reality they

Waves are a form of potential energy that can be transported across hundreds to thousands of ean to be released as kinetic energy when they shoal and break. Waves are

(L) (crest to crest) and period (T) (time between successive crests). The longer the period the longer and faster the waves, as wave

er shallow water their √gd where g is the gravitational

constant. For this reason waves slow down as they move towards the shore, with a 10 sec ed to 7 km/hr (4 mph) in 5 m water

are produced by the gravitational pull of the Moon and Sun acting on a rotating Earth. This pull produces a very slight bulge in the ocean, which we know as tide. The tides and the currents they generate are responsible for about 50% of the marine energy delivered to the coast. The major impact of tides is to shift the shoreline between high and low tide, and to

and estuaries, currents



Figure 3 Tidal inlet at Merrimbula, Australia. Tidal currents ebb and flood though the narrow inlet moving marine sand from the beach into the inlet to form a deesandy tidal delta. © 2012 Nature Education Courtesy of A. D. Short. All rights reserved.

Wind and currents.

Winds blowing over the oceans are responsible for generatithey can generate local seas —driven currents which in places can result in upwelling and downwelling. Finally, when blowing over the beach, they can transport sand

Fluvial-deltaic systems.

Fluvial systems deliver sediment to the coast where it is deposited in estuaries and deltas. Depending on their location, deltas are also acted on by waves, tides, and other currents, and shaped to suit the prevailing processes. Sediment can also be moved beach and barrier systems (Figure 4).



Tidal inlet at Merrimbula, Australia. Tidal currents ebb and flood though the narrow inlet moving marine sand from the beach into the inlet to form a deep tidal channel and shallow

Courtesy of A. D. Short. All rights reserved.

Winds blowing over the oceans are responsible for generating ocean waves. Nearer the coast — they can move the ocean surface and generate locally wind

driven currents which in places can result in upwelling and downwelling. Finally, when blowing over the beach, they can transport sand inland to build coastal sand dunes.

Fluvial systems deliver sediment to the coast where it is deposited in estuaries and deltas. Depending on their location, deltas are also acted on by waves, tides, and other currents, and

d to suit the prevailing processes. Sediment can also be moved longshorebeach and barrier systems (Figure 4).

Tidal inlet at Merrimbula, Australia. Tidal currents ebb and flood though the narrow inlet p tidal channel and shallow

ng ocean waves. Nearer the coast they can move the ocean surface and generate locally wind

driven currents which in places can result in upwelling and downwelling. Finally, when inland to build coastal sand dunes.

Fluvial systems deliver sediment to the coast where it is deposited in estuaries and deltas. Depending on their location, deltas are also acted on by waves, tides, and other currents, and

longshore to supply



Figure 4 The Gasgoyne River delta in Western Australia delivers large volumes of sand to the coast where it is deposited in river moudowndrift spits, barriers, and dunes.© 2012 Nature Education Courtesy of A. D. Short. All rights reserved.

Sea level.

Sea level determines the position of the shoreline. During the last glacial maxima (ice age) 18,000 years ago, sea level was 120 m below present, and the continental shelves were exposed. It then rose, reaching present sea level around 6,000 years ago, after which it was relatively stable. Now, with climate change, it is beginning to rise again, and may rise as much as 1 m over the next 100 years, triggering shoreline retreat, inundation, and erosion.

Beach Systems

What is a beach?

Beaches are wave-deposited accumulations of sedia base to reside on, usually the bedrock geology, waves to shape them, sediment to form them, and most are also affected by tides. The beach extends from wave base where waves begin to feel bottom and shoal, acrolimit of wave swash (Figure 5). In the coastal zone ocean waves are transformed by shoaling, breaking, and swash. In doing so they interact with the seabed, and determine the beach morphology or shape, a process called



The Gasgoyne River delta in Western Australia delivers large volumes of sand to the coast where it is deposited in river mouth shoals and slowly reworked longshore to supply downdrift spits, barriers, and dunes.


position of the shoreline. During the last glacial maxima (ice age) 18,000 years ago, sea level was 120 m below present, and the continental shelves were exposed. It then rose, reaching present sea level around 6,000 years ago, after which it was

y stable. Now, with climate change, it is beginning to rise again, and may rise as much as 1 m over the next 100 years, triggering shoreline retreat, inundation, and erosion.

deposited accumulations of sediment located at the shoreline. They require a base to reside on, usually the bedrock geology, waves to shape them, sediment to form them, and most are also affected by tides. The beach extends from wave base where waves begin to feel bottom and shoal, across the nearshore zone, though the surf zone to the upper

(Figure 5). In the coastal zone ocean waves are transformed by shoaling, breaking, and swash. In doing so they interact with the seabed, and determine the beach

e, a process called beach morphodynamics.

The Gasgoyne River delta in Western Australia delivers large volumes of sand to the coast th shoals and slowly reworked longshore to supply

position of the shoreline. During the last glacial maxima (ice age) 18,000 years ago, sea level was 120 m below present, and the continental shelves were exposed. It then rose, reaching present sea level around 6,000 years ago, after which it was

y stable. Now, with climate change, it is beginning to rise again, and may rise as much as 1 m over the next 100 years, triggering shoreline retreat, inundation, and erosion.

ment located at the shoreline. They require a base to reside on, usually the bedrock geology, waves to shape them, sediment to form them, and most are also affected by tides. The beach extends from wave base where waves

ss the nearshore zone, though the surf zone to the upper (Figure 5). In the coastal zone ocean waves are transformed by shoaling,

breaking, and swash. In doing so they interact with the seabed, and determine the beach



Figure 5 An idealised cross-section of a wavewhich contains the subaerial or 'dry' beach (runnel, berm, and beach face) and is dominated by swash processes; the energetic surf zone (bars and channels) with its breaking waves and surf zone currents; and the nearshore zone extending out to wave base where waves shoal building a concave upward slope.© 2012 Nature Education Reprinted with permission from Short & Woodroffe 2009. All rights reserved.

Beach sediment — types & sources.

All beaches consist of sedimentboulders. The finer sand result in very stacked as steep as 20° (Figures 6a and 6b). Most beaches with fine to medium sand have a swash zone gradient between 1

In the mid latitudes most beaches are composed of siliceous or quartz sand grains defrom erosion. In the topics, coral reef detritus and shells known as 'carbonate sediment' tend to dominate, (Figures 6c and 6d), while in higher latitudes physical weathering produces coarse rock fragments and gravel.



section of a wave-dominated beach system consisting of the swash zone which contains the subaerial or 'dry' beach (runnel, berm, and beach face) and is dominated

e energetic surf zone (bars and channels) with its breaking waves and surf zone currents; and the nearshore zone extending out to wave base where waves shoal building a concave upward slope.


types & sources.

sediment, which can range in size from sand up to cobbles and boulders. The finer sand result in very low gradient (~1°) beaches while cobbles may be stacked as steep as 20° (Figures 6a and 6b). Most beaches with fine to medium sand have a swash zone gradient between 1–8°.

In the mid latitudes most beaches are composed of siliceous or quartz sand grains defrom erosion. In the topics, coral reef detritus and shells known as 'carbonate sediment' tend to dominate, (Figures 6c and 6d), while in higher latitudes physical weathering produces coarse rock fragments and gravel.

dominated beach system consisting of the swash zone which contains the subaerial or 'dry' beach (runnel, berm, and beach face) and is dominated

e energetic surf zone (bars and channels) with its breaking waves and surf zone currents; and the nearshore zone extending out to wave base where waves shoal


, which can range in size from sand up to cobbles and low gradient (~1°) beaches while cobbles may be

stacked as steep as 20° (Figures 6a and 6b). Most beaches with fine to medium sand have a

In the mid latitudes most beaches are composed of siliceous or quartz sand grains derived from erosion. In the topics, coral reef detritus and shells known as 'carbonate sediment' tend to dominate, (Figures 6c and 6d), while in higher latitudes physical weathering produces





Figure 6 a) A steep cobble-boulder beach at Catfish Bay, Western Australia. (b) Lowsand beach at Ball Bay, Queensland. (c) Shell Beach, Western Australia is composed entirely of the white cockle shell Fragum erugatum© 2012 Nature Education Courtesy of A. D. Short. All rights reserved.

Sediments may therefore be derived from the land and delivered via rivers, glaciers and shoreline erosion, and from marine organisms in theonshore by wave, tide, and wind driven currents to form beaches. A positive sediment supply produces beach accretion while when negative beaches erode (Figure 7).



lder beach at Catfish Bay, Western Australia. (b) Lowsand beach at Ball Bay, Queensland. (c) Shell Beach, Western Australia is composed entirely

Fragum erugatum. (d) Close up view of the cockle shell.Courtesy of A. D. Short. All rights reserved.

Sediments may therefore be derived from the land and delivered via rivers, glaciers and shoreline erosion, and from marine organisms in the sea. Once at the shore they are moved onshore by wave, tide, and wind driven currents to form beaches. A positive sediment supply produces beach accretion while when negative beaches erode (Figure 7).

lder beach at Catfish Bay, Western Australia. (b) Low-gradient fine sand beach at Ball Bay, Queensland. (c) Shell Beach, Western Australia is composed entirely

. (d) Close up view of the cockle shell.

Sediments may therefore be derived from the land and delivered via rivers, glaciers and sea. Once at the shore they are moved

onshore by wave, tide, and wind driven currents to form beaches. A positive sediment supply





Figure 7 a) Greenmount Beach in Queensland, Australinourishment. b) Collaroy Beach in NSW, Australia has been eroding, resulting in the construction of rock seawalls. © 2012 Nature Education Courtesy of A. D.

Beach sub-systems.

At the beach the three zones of wave transformation (shoaling, breaking, and swash) produce three morphologically distinct subgradient (~1°) concave upward profile, smooth in outline, with small waveand generally onshore sediment movement. As they shoal they interact with the seabed, slowing down and increasing in steepness and height (Figure 8).

Figure 8 View of Makapu Beach, Hawaacross and interact with the nearshore zone, then breaking across the surf zone.© 2012 Nature Education Courtesy of A. D. Short. All rights

The surf zone is the most dynamic part of the beach and extends from the breaker zone to the shore. Waves break when the water depth is approximately 1.5 times the wave height. They can break as a spilling breaker on low gradient slopes, a plugradients, or a surging wave on steep slopes. In breaking, waves transform their potential energy to kinetic energy, which is initially manifest as the broken wave of translation, or



a) Greenmount Beach in Queensland, Australia widened by 200 m as a result of beach nourishment. b) Collaroy Beach in NSW, Australia has been eroding, resulting in the


At the beach the three zones of wave transformation (shoaling, breaking, and swash) produce three morphologically distinct sub-systems (Figure 5). The shoaling wave zone

upward profile, smooth in outline, with small wave-and generally onshore sediment movement. As they shoal they interact with the seabed, slowing down and increasing in steepness and height (Figure 8).

View of Makapu Beach, Hawaii, showing waves shoaling and steepening as they travel across and interact with the nearshore zone, then breaking across the surf zone.


is the most dynamic part of the beach and extends from the breaker zone to the shore. Waves break when the water depth is approximately 1.5 times the wave height. They can break as a spilling breaker on low gradient slopes, a plunging wave on moderate gradients, or a surging wave on steep slopes. In breaking, waves transform their potential energy to kinetic energy, which is initially manifest as the broken wave of translation, or

a widened by 200 m as a result of beach nourishment. b) Collaroy Beach in NSW, Australia has been eroding, resulting in the

At the beach the three zones of wave transformation (shoaling, breaking, and swash) produce shoaling wave zone builds a low

-generated ripples and generally onshore sediment movement. As they shoal they interact with the seabed,

ii, showing waves shoaling and steepening as they travel across and interact with the nearshore zone, then breaking across the surf zone.

is the most dynamic part of the beach and extends from the breaker zone to the shore. Waves break when the water depth is approximately 1.5 times the wave height. They

nging wave on moderate gradients, or a surging wave on steep slopes. In breaking, waves transform their potential energy to kinetic energy, which is initially manifest as the broken wave of translation, or



wave bore, which moves shoreward as broken white water. At the shoreline the currents can be deflected longshore and water may return seaward as a rip current.

Surf zone currents can transport sediment onshore, longshore and offshore and build the (sand) bars and troughs that occupy the surf zone (Figure 5). The number and location of the bars is a product of infragravity waves, a low frequency (greater 30 sec period) wave produced by sets of higher and lower waves and which is enhanced by wave breaking across the surf zone. The longer the infragravity wave period the more widely spaced the bar(s). Another form of infragravity wave called edge waves also influence the longshore spacing of rip currents and channels, which are typically 200–300 m apart on ocean beaches. Rip currents are narrow, seaward moving currents that move seaward though the surf zone, often in a deeper rip channel (Figure 9a). They are a mechanism for returning the water back out to sea, and a conduit to transport seaward eroded beach sediment (Figure 9b) during high seas. They are also a major hazard to beach goers and responsible for most beach rescues and drowning (Short 1999).



Figure 9 a) Low waves breaking on a shallow bar and flowing shoreward into a rip feeder channel. The dye highlights the rip feeder current flowing along the turning to flow seaward in the deeper rip channel. b) A rip current (center) carrying suspended sediment flowing out beyond the surf zone as a rip head, with an earlier rip head meandering to the right, Miles Beach, Tasmania.© 2012 Nature Education Courtesy of A. D. Short. All rights reserved.

When the broken wave reaches the base of the wet beach it collapses and runs up the beach face as swash or uprush in the



a) Low waves breaking on a shallow bar and flowing shoreward into a rip feeder channel. The dye highlights the rip feeder current flowing along the base of the beach face, then turning to flow seaward in the deeper rip channel. b) A rip current (center) carrying suspended sediment flowing out beyond the surf zone as a rip head, with an earlier rip head meandering to the right, Miles Beach, Tasmania.


When the broken wave reaches the base of the wet beach it collapses and runs up the beach face as swash or uprush in the swash zone (Figure 10). The uprush stops toward the top of

a) Low waves breaking on a shallow bar and flowing shoreward into a rip feeder channel. base of the beach face, then

turning to flow seaward in the deeper rip channel. b) A rip current (center) carrying suspended sediment flowing out beyond the surf zone as a rip head, with an earlier rip head

When the broken wave reaches the base of the wet beach it collapses and runs up the beach (Figure 10). The uprush stops toward the top of



the slope, some percolates into the beach, the remainder flows back down the beach as backwash. Both actions produce a relatively steep seaward sloping swash zone or beach face, which can range from 1 to 20°. As sediment is deposited in the swash zone it can build a berm, a near horizontal to slightly landwardpeople sit when they go to the beach. The swash zone may also contain about every 20 to 30 m and produced by another form of edge wave (Figure 11).

Figure 10 Wave runup on the steep beach face at Ke lli Beach, Hawaii.© 2012 Nature Education Courtesy of A. D. Short. All rights r



the slope, some percolates into the beach, the remainder flows back down the beach as backwash. Both actions produce a relatively steep seaward sloping swash zone or beach face,

o 20°. As sediment is deposited in the swash zone it can build a , a near horizontal to slightly landward-dipping sand surface, the area where most

people sit when they go to the beach. The swash zone may also contain beach cuspsto 30 m and produced by another form of edge wave (Figure 11).

Wave runup on the steep beach face at Ke lli Beach, Hawaii. Courtesy of A. D. Short. All rights reserved.

the slope, some percolates into the beach, the remainder flows back down the beach as backwash. Both actions produce a relatively steep seaward sloping swash zone or beach face,

o 20°. As sediment is deposited in the swash zone it can build a dipping sand surface, the area where most

beach cusps, spaced to 30 m and produced by another form of edge wave (Figure 11).



Figure 11 A steep reflective beach with well developed high tide beach cusps at Hammer Head, Western Australia. © 2012 Nature Education Courtesy of A. D. Short. All rights reserved.

Beach types.

Beaches can range from low energy systems, where small waves lap against the shore, to those with high waves breaking across several hundred meters of surf zone. They can also be exposed to micro (<2 m), meso (2accommodate the range of wave heights, tide ranges and beach sediment (sand to boulders) beaches are divided into the three basic types: wavedominated, based on the relative tide range (RTR) (Short 2006, http://www.ozcoasts.org.au/conceptual_mods/index.jspRTR = TR/H

where TR is the spring tide range.

Wave-dominated beaches have an RTR tide range less than three times the average wave height (RTR < 3). They consist of three states Reflective beaches are produced by lower waves (H<0.5 m), longer wave periods, and coarser sediment, such that all coarse sand and cobble/boulder beaches are reflective (Figure 12). They consist of a relatively steep beach face (5the base of the beach and running up the beach face and returning as bthe beach face. There is no bar or surf zone (Figure 11).



A steep reflective beach with well developed high tide beach cusps at Hammer Head,


Beaches can range from low energy systems, where small waves lap against the shore, to those with high waves breaking across several hundred meters of surf zone. They can also be exposed to micro (<2 m), meso (2–4 m), macro (4–8 m) and mega tides (>8 m). To accommodate the range of wave heights, tide ranges and beach sediment (sand to boulders) beaches are divided into the three basic types: wave-dominated, tide-modified, and tidedominated, based on the relative tide range (RTR) (Short 2006, see also http://www.ozcoasts.org.au/conceptual_mods/index.jsp).

where TR is the spring tide range.

have an RTR tide range less than three times the average wave height (RTR < 3). They consist of three states — reflective, intermediate, and dissipative.

are produced by lower waves (H<0.5 m), longer wave periods, and arser sediment, such that all coarse sand and cobble/boulder beaches are reflective (Figure

12). They consist of a relatively steep beach face (5–20°), with waves breaking by surging at the base of the beach and running up the beach face and returning as backwash to ‘reflect' off the beach face. There is no bar or surf zone (Figure 11).

A steep reflective beach with well developed high tide beach cusps at Hammer Head,

Beaches can range from low energy systems, where small waves lap against the shore, to those with high waves breaking across several hundred meters of surf zone. They can also be

ides (>8 m). To accommodate the range of wave heights, tide ranges and beach sediment (sand to boulders)

modified, and tide-

have an RTR tide range less than three times the average wave reflective, intermediate, and dissipative.

are produced by lower waves (H<0.5 m), longer wave periods, and arser sediment, such that all coarse sand and cobble/boulder beaches are reflective (Figure

20°), with waves breaking by surging at ackwash to ‘reflect' off



Figure 12 A plot of breaker wave height versus sand size, together with wave period, that can be used to determine the approximate beach state for wavedetermine the breaker wave height, period and grain size (mm). Read off the wavesand size, then use the period to determine where the boundary of reflective/intermediate, or intermediate/dissipative beaches lies. Ω = 1 along solid T lines and 6 along dashed T lines. Below the solid lines Ω < 1 and the beach is reflective; beach is dissipative; between the solid and dashed lines Ω is between 1 and 6 and the beach is intermediate. (Ω=Hb/WsT and is known as the dimensionless fall velocity).© 2012 Nature Education Reprinted with permission from Short 1999. All rights reserved.



A plot of breaker wave height versus sand size, together with wave period, that can be used to determine the approximate beach state for wave-dominated beaches. To use the chart, determine the breaker wave height, period and grain size (mm). Read off the wavesand size, then use the period to determine where the boundary of reflective/intermediate, or intermediate/dissipative beaches lies. Ω = 1 along solid T lines and 6 along dashed T lines. Below the solid lines Ω < 1 and the beach is reflective; above the dashed lines Ω > 6 and the beach is dissipative; between the solid and dashed lines Ω is between 1 and 6 and the beach is

T and is known as the dimensionless fall velocity).Reprinted with permission from Short 1999. All rights reserved.

A plot of breaker wave height versus sand size, together with wave period, that can be used to To use the chart,

determine the breaker wave height, period and grain size (mm). Read off the wave height and sand size, then use the period to determine where the boundary of reflective/intermediate, or intermediate/dissipative beaches lies. Ω = 1 along solid T lines and 6 along dashed T lines.

above the dashed lines Ω > 6 and the beach is dissipative; between the solid and dashed lines Ω is between 1 and 6 and the beach is

T and is known as the dimensionless fall velocity). Reprinted with permission from Short 1999. All rights reserved.



Intermediate beaches are common on open coasts and require moderate waves (H=0.5m) and fine to medium sand. They are characterized by a surf zone with o100 m wide. The bar is usually cut by regular rip channels and currents (Figure 13).

Figure 13 Well-developed intermediate beach containing transverse bars and rip channels along Lighthouse Beach, Australia. Note the waves breaking the deeper darker rip channels. Also note the rhythmic shoreline protruding in lee of the bars and forming an embayment in lee of the rips.© 2012 Nature Education Courtesy of A. D. Short. All rights reserved.

Dissipative beaches require both high waves (H>2.5 m) and fine sand. They have a low gradient swash (~1°) and 300–break on the outer then inner bsurf zone (Figure 14).



are common on open coasts and require moderate waves (H=0.5m) and fine to medium sand. They are characterized by a surf zone with one or two bars up to 100 m wide. The bar is usually cut by regular rip channels and currents (Figure 13).

developed intermediate beach containing transverse bars and rip channels along Lighthouse Beach, Australia. Note the waves breaking on the bars, with no waves breaking in the deeper darker rip channels. Also note the rhythmic shoreline protruding in lee of the bars and forming an embayment in lee of the rips.


require both high waves (H>2.5 m) and fine sand. They have a low –500 m wide surf zone containing at least two bars. Waves

break on the outer then inner bar(s), thereby dissipating their energy as the move across the

are common on open coasts and require moderate waves (H=0.5–2.5 ne or two bars up to

100 m wide. The bar is usually cut by regular rip channels and currents (Figure 13).

developed intermediate beach containing transverse bars and rip channels along on the bars, with no waves breaking in

the deeper darker rip channels. Also note the rhythmic shoreline protruding in lee of the bars

require both high waves (H>2.5 m) and fine sand. They have a low 500 m wide surf zone containing at least two bars. Waves ar(s), thereby dissipating their energy as the move across the



Figure 14 Long, high Southern Ocean swell arriving at Dog Fence Beach, South Australia. The swell breaks over the wide outer bar, reforms in the central trough, then brresulting up to 10 lines of breakers and a 500 m wide dissipative beach and surf zone.© 2012 Nature Education Courtesy of A. D. Short. All rights reserved.

Tide-modified beaches have an RTR between 3 and 10, implying tide range is increasing and/or wave height decreasing. They usually have a steep, coarserhigh tide beach. This is fronted by a wide, finerintertidal zone, up to 200 m wide, then a low tide surf zone which may contain bars and rip channels (Figure 15).



Long, high Southern Ocean swell arriving at Dog Fence Beach, South Australia. The swell breaks over the wide outer bar, reforms in the central trough, then breaks across the inner bar, resulting up to 10 lines of breakers and a 500 m wide dissipative beach and surf zone.


have an RTR between 3 and 10, implying tide range is increasing and/or wave height decreasing. They usually have a steep, coarser-grained, cusped, reflective, high tide beach. This is fronted by a wide, finer-grained, low gradient, often featureintertidal zone, up to 200 m wide, then a low tide surf zone which may contain bars and rip

Long, high Southern Ocean swell arriving at Dog Fence Beach, South Australia. The swell eaks across the inner bar,

resulting up to 10 lines of breakers and a 500 m wide dissipative beach and surf zone.

have an RTR between 3 and 10, implying tide range is increasing grained, cusped, reflective,

grained, low gradient, often featureless, intertidal zone, up to 200 m wide, then a low tide surf zone which may contain bars and rip



Figure 15 A steep reflective high tide beach face fronted by a 100 m wide tidecrossed by shallow drainage c© 2012 Nature Education Courtesy of A. D. Short. All rights reserved.

Tide-dominated beaches have an RTR between 10 and approximately 50, implying high tides and/or very low waves (H<<0.3 m). They consist of a low elevation, coarseirregular, high tide beach, fronted by low gradient (<<1°) interthat may be hundreds of meters wide (Figure 16). Beyond an RTR of 50, t



A steep reflective high tide beach face fronted by a 100 m wide tide-modified low tide terrace crossed by shallow drainage channels at North Harbour Beach, Australia.


have an RTR between 10 and approximately 50, implying high tides and/or very low waves (H<<0.3 m). They consist of a low elevation, coarseirregular, high tide beach, fronted by low gradient (<<1°) inter-tidal sand, and even mud flats that may be hundreds of meters wide (Figure 16). Beyond an RTR of 50, tidal flats prevail.

modified low tide terrace

have an RTR between 10 and approximately 50, implying high tides and/or very low waves (H<<0.3 m). They consist of a low elevation, coarse-grained,

tidal sand, and even mud flats idal flats prevail.



Figure 16 A narrow high tide beach fronted by 1 km wide interSouth Australia. © 2012 Nature Education Courtesy of A. D. Short. All right

An additional beach type consists of a high tide reflective beach face fronted by intertidal rocks flats, and in the tropics a high tide beach fronted by a fringing coral reef flat (Figure 17). Furthermore any beach located in the high latitufreezing air and water temperatures leading to the development of sea ice, shoreface ice, and a frozen snow covered beach (Figure 18).



A narrow high tide beach fronted by 1 km wide inter-tidal sand flats, upper Spencer Gulf,


An additional beach type consists of a high tide reflective beach face fronted by intertidal rocks flats, and in the tropics a high tide beach fronted by a fringing coral reef flat (Figure 17). Furthermore any beach located in the high latitudes will be seasonally exposed to freezing air and water temperatures leading to the development of sea ice, shoreface ice, and a frozen snow covered beach (Figure 18).

tidal sand flats, upper Spencer Gulf,

An additional beach type consists of a high tide reflective beach face fronted by intertidal rocks flats, and in the tropics a high tide beach fronted by a fringing coral reef flat (Figure

des will be seasonally exposed to freezing air and water temperatures leading to the development of sea ice, shoreface ice, and



Figure 17 A high tide beach fringed by coral reef at Turquoise Bay, Western AustraliaNingaloo Marine Park. © 2012 Nature Education Courtesy of A. D. Short. All rights reserved.



A high tide beach fringed by coral reef at Turquoise Bay, Western Australia


A high tide beach fringed by coral reef at Turquoise Bay, Western Australia, part of the





Figure 18 The beach at Pingok Island, north Alaska, shown a) during summer, with floatithe shore; b) during freeze-up, with snow and sea ice accumulating; and c) the frozen winter beach and ocean. © 2012 Nature Education Courtesy of A. D. Short. All rights reserved.

Beaches and barriers.

Beach systems are an essential component of a larger scale coastal landform called which are long-term accumulation of wave, tide, and wind deposited marine sediment (usually sand) at the shore. They consist of a beach fromonshore, via wave overwash and/or wind blown sand, or alongshore, to form spits and move into tidal inlets (Figure 3). When separated from the mainland by lagoons and marshes (Figure 19) they are called barrier islandsGulf coasts. Some are backed by large dune systems as along the Oregon coast.

Figure 19 A coastal sand barrier consisting of a beach and vegetated dunes, backed by a lagoon, at Big Beach, Queensland, Australia.© 2012 Nature Education Courtesy of A. D. Short. All rights reserved.



The beach at Pingok Island, north Alaska, shown a) during summer, with floatiup, with snow and sea ice accumulating; and c) the frozen winter


Beach systems are an essential component of a larger scale coastal landform called term accumulation of wave, tide, and wind deposited marine sediment

(usually sand) at the shore. They consist of a beach from which sand is transported either onshore, via wave overwash and/or wind blown sand, or alongshore, to form spits and move into tidal inlets (Figure 3). When separated from the mainland by lagoons and marshes

barrier islands (Figure 20), which occur along the US East and Gulf coasts. Some are backed by large dune systems as along the Oregon coast.

A coastal sand barrier consisting of a beach and vegetated dunes, backed by a lagoon, at Big Beach, Queensland, Australia.


The beach at Pingok Island, north Alaska, shown a) during summer, with floating ice against up, with snow and sea ice accumulating; and c) the frozen winter

Beach systems are an essential component of a larger scale coastal landform called barriers, term accumulation of wave, tide, and wind deposited marine sediment

which sand is transported either onshore, via wave overwash and/or wind blown sand, or alongshore, to form spits and move into tidal inlets (Figure 3). When separated from the mainland by lagoons and marshes

gure 20), which occur along the US East and Gulf coasts. Some are backed by large dune systems as along the Oregon coast.

A coastal sand barrier consisting of a beach and vegetated dunes, backed by a lagoon, at Big



Figure 20 A series of low barrier islands separated by tidal inlets, at Corner Inlet, Victoria, Australia.© 2012 Nature Education Courtesy of A. D. Short. All rights reserved.

Harbor From Wikipedia, the free encyclopedia

For other uses, see Harbor (disambiguation)

Capri harbor, Italy seen from Anacapri

A harbor or harbour (see spelling differencesboats, and barges can seek shelter from

Harbors can be natural or artificial. An artificial harbor has deliberately constbreakwaters, sea walls, or jettysand these require maintenance by further periodic dredging. An example of the artificial



A series of low barrier islands separated by tidal inlets, at Corner Inlet, Victoria, Australia.Courtesy of A. D. Short. All rights reserved.

From Wikipedia, the free encyclopedia

Harbor (disambiguation).

Anacapri

spelling differences), or haven, is a body of water where can seek shelter from stormy weather, or else are stored for future use.

Harbors can be natural or artificial. An artificial harbor has deliberately constjettys, or otherwise, they could have been constructed by

and these require maintenance by further periodic dredging. An example of the artificial

A series of low barrier islands separated by tidal inlets, at Corner Inlet, Victoria, Australia.

a body of water where ships, , or else are stored for future use.

Harbors can be natural or artificial. An artificial harbor has deliberately constructed , or otherwise, they could have been constructed by dredging,

and these require maintenance by further periodic dredging. An example of the artificial



harbor is Long Beach Harbor, California, which was an array of salt marshes and tidal flats too shallow for modern merchant ships before it was first dredged in the early 20th century.[1]

In contrast, a natural harbor is surrounded on several sides by prominences of land. Examples of natural harbors include San Francisco Bay, California and San Diego Harbor, California.

Harbors and ports are often confused with each other. A port is a facility for loading and unloading vessels; ports are usually located in harbors.

Artificial harbors

Artificial harbors are frequently built for use as ports. The oldest artificial harbor known is the Ancient Egyptian site at Wadi al-Jarf, on the Red Sea coast, which is at least 4500 years old (ca. 2600-2550 BC, reign of King Khufu). The largest artificially created harbor is Jebel Ali in Dubai.[2] Other large and busy artificial harbors are located at: Rotterdam, The Netherlands; Port of Houston, Texas; Port of Long Beach, California; and Port of Los Angeles in San Pedro, California.

The Ancient Carthaginians constructed fortified, artificial harbors called cothons.

Natural harbors

A natural harbor in Vizhinjam, India

A natural harbor is a landform where a part of a body of water is protected and deep enough to furnish anchorage. Many such harbors are rias. Natural harbors have long been of great strategic naval and economic importance, and many great cities of the world are located on them. Having a protected harbor reduces or eliminates the need for breakwaters as it will result in calmer waves inside the harbor. Some examples are New York Harbor in the United States; Poole Harbour in England; Kingston Harbour in Jamaica; Grand Harbour in Malta; Subic Bay in Zambales, the Philippines; Sydney Harbour in Australia; Pearl Harbor in Hawaii; Trincomalee Harbour in Sri Lanka; San Francisco Bay in California; Visakhapatnam Harbour in Andhra Pradesh, India; Killybegs in County Donegal Ireland; Halifax Harbour in Nova Scotia, Canada,Cork Harbour, Ireland and Waitemata Harbour in Auckland, New Zealand.

Ice-free harbors



For harbors near the North and South Poles, being ice-free is an important advantage, especially when it is year-round. Examples of these include Murmansk, Russia; Pechenga, Russia; St. Petersburg, Russia; Hammerfest, Norway; Vardø, Norway; and Prince Rupert Harbour, Canada. The world's southmost harbor, located at Antarctica's Winter Quarters Bay (77° 50′ South), is potentially ice-free, depending on the summertime pack ice conditions.[3]

Important harbors

The tiny harbor at the village of Clovelly, Devon, England

Old Harbor in Lüneburg, Germany.

The harbor of Piraeus in Greece.

Port Jackson, Sydney.



The harbor of Gorey, Jersey falls dry at low tide.

Port of Kaohsiung

Although the world's busiest port is a hotly contested title, in 2006 the world's busiest harbor by cargo tonnage was the Port of Shanghai.[4]

The following are large natural harbors:

• Algeciras, Spain • Amsterdam, Port of Amsterdam, Netherlands • Antwerp, Port of Antwerp, Flanders, Belgium • Baltimore's Inner Harbor, Maryland, United States • Boston Harbor, Massachusetts, United States • Bremerhaven, Germany • Buenos Aires, Argentina • Busan, Korea • Cartagena, Colombia • Charleston, South Carolina, United States • Port of Chittagong, Chittagong City, Bangladesh • Cork Harbour, Ireland • Duluth–Superior harbor, Duluth, Minnesota, United States • Durban, South Africa • Falmouth, Cornwall, England, United Kingdom • Freetown Harbour, Sierra Leone • Golden Horn, Istanbul, Turkey • Gothenburg, Sweden • Grand Harbour, Malta • Gwangyang, Korea • Hai Phong Port, Haiphong, Vietnam • Halifax Harbour, Nova Scotia, Canada • Hamburg Harbour, Germany • Hampton Roads, Norfolk, Virginia, United States • Havana Harbor • Incheon, Korea • Izmir, Turkey • Port of Jakarta (Tanjung Priok), Jakarta, Indonesia • Karachi, Sindh, Pakistan • Kingston, Jamaica • Kobe Harbour, Kobe, Japan



• Kochi, India • Lisbon, Portugal • Lushunkou, Dalian, China • Mahón, Minorca, Spain • Manila Bay, Philippines • Maputo, Mozambique • Milford Haven, Wales, United Kingdom • Montevideo, Uruguay • Mumbai, India • Nassau, Bahamas • New York Harbor, United States • Oslofjord, Norway • Pearl Harbor, Honolulu, Hawaii, United States • Piraeus, Attiki, Greece • Plymouth Sound, Devon, England, United Kingdom • Poole Harbour, Dorset, England, United Kingdom • Port Jackson, Sydney, New South Wales, Australia • Port Phillip, Melbourne, Victoria, Australia • Portland Harbor, Casco Bay, Maine, United States • Provincetown Harbor, Provincetown, Massachusetts, United States • Rio de Janeiro, Guanabara Bay, Brazil • Rotterdam, Port of Rotterdam, Netherlands • Salvador, All Saint's Bay, Brazil • San Antonio, Chile • San Diego Bay, San Diego, California, United States • San Francisco Bay, California, United States • Sankt Petersburg, Russia • Sevastopol Harbour, Sevastopol, Ukraine • Subic Bay, Zambales, Philippines • Tanger-Med, Tangier, Morocco • Tauranga Harbour, Tauranga, New Zealand • Tokyo Bay, Tokyo, Japan • Trincomalee, Sri Lanka • Tuticorin, Tamil Nadu, India • Port of Tyne, Tyne & Wear, United Kingdom • Ulsan, Korea • Vancouver, Canada • Victoria Harbour, Hong Kong • Visakhapatnam Port, Andhra Pradesh, India • Vizhinjam, Trivandrum, India • Waitemata Harbour, Auckland, New Zealand • Willemstad, Curaçao • Wellington Harbour, New Zealand



Port of Szczecin, Poland

Other notable harbors include:

• Belém, Brazil • Port of Bruges-Zeebrugge, Flanders, Belgium • Port of Genoa, Italy • Port of Gdańsk, Poland • Kahului, Hawaii, United States • Kaipara Harbour, New Zealand • Kaohsiung, Taiwan • Keelung, Taiwan • Keppel Harbour, Singapore • Kilindini Harbour, Kenya • Manukau Harbour, Auckland, New Zealand • New Haven Harbor, Connecticut, United States • Portland Harbour, Dorset, England, United Kingdom • Rades, Tunisia • Rio Grande, Brazil • San Juan, Puerto Rico, United States • Scapa Flow, Orkney Islands, Scotland, United Kingdom • Sydney Harbour, Australia • Port of Szczecin, Poland • Trondheim, Norway • Valparaiso, Chile • Vladivostok, Russia

Ports and harbours of India

C

• Chennai Port

D

• Dugarajapatnam Port

E

H

• Hazira Port

K

• Kakinada Port • Kanhangad • Kollam Port

P

• Port Cornwallis • Port of Kolkata

T

• Tuna Port

V



• Ennore Port

G

• Gangavaram Port

• SITE SELECTION FOR HARBOURS • 2. At the time of selection for a harbour, greatcategories play a great role in the choice of site for a harbour. Availability of cheap land and construction¬ material. Natural protection from waves and winds.communication facilities.¬ Industrial development of the locality.foundation conditions.¬ Availability of fresh water and electrical• 3. Favorable marine conditions.the harbor.¬ The site should have maximum natural protection from winds and waves. It should have sufficiently large pool of water, with adequate depth to accommodate the expected shipping needs as well as to permit the future needbe favorable for structures as well as for navigation. To meet this requirement the site should have low tidal range and small tidal currents. • 4. There should not be severe wind and waves and there should be leAlso there should be no fog problem at the site. The sea bed should be such that it would hold ship anchors and would not involve much capital and dredging maintenance cost. There should not be excessive situation nor scour should poconditions, the sub- soil for foundation purposes should be favorable. The site to be selected should be preferably on an established trade route and have trade links with other parts of the country through rail,road

• 5. air and telephone etc. The hinter land should be productive enouAll these conditions are desirable but not necessary.

Dredging


"Dredge" redirects here. For other uses, see

"Dredgers" redirects here. For the German municipality, see



• Visakhapatnam Port

SITE SELECTION FOR HARBOURS of selection for a harbour, great♣ care should be exercised. Following

categories play a great role in the choice of site for a harbour. Availability of cheap land and material. Natural protection from waves and winds.¬ Transport and

Industrial development of the locality.¬ Sea bed, sub soil and Availability of fresh water and electrical¬ energy.

Favorable marine conditions.¬ Defense and strategic aspects.¬ Traffic potentiality of The site should have maximum natural protection from winds and waves. It

should have sufficiently large pool of water, with adequate depth to accommodate the expected shipping needs as well as to permit the future needs. The marine conditions should be favorable for structures as well as for navigation. To meet this requirement the site should have low tidal range and small tidal currents.

There should not be severe wind and waves and there should be less littoral drift etc. Also there should be no fog problem at the site. The sea bed should be such that it would hold ship anchors and would not involve much capital and dredging maintenance cost. There should not be excessive situation nor scour should pose a problem. Apart from above

soil for foundation purposes should be favorable. The site to be selected should be preferably on an established trade route and have trade links with other parts of the

air and telephone etc. The hinter land should be productive enough to support the trade. All these conditions are desirable but not necessary.


"Dredge" redirects here. For other uses, see Dredge (disambiguation).

"Dredgers" redirects here. For the German municipality, see Dreggers.

sakhapatnam Port

care should be exercised. Following categories play a great role in the choice of site for a harbour. Availability of cheap land and

Transport and Sea bed, sub soil and

energy. Traffic potentiality of

The site should have maximum natural protection from winds and waves. It should have sufficiently large pool of water, with adequate depth to accommodate the

s. The marine conditions should be favorable for structures as well as for navigation. To meet this requirement the site should

ss littoral drift etc. Also there should be no fog problem at the site. The sea bed should be such that it would hold ship anchors and would not involve much capital and dredging maintenance cost. There

se a problem. Apart from above soil for foundation purposes should be favorable. The site to be selected

should be preferably on an established trade route and have trade links with other parts of the

gh to support the trade.



A grab dredge

Dredging is an excavation activity or operation usually carried out at least partly underwater, in shallow seas or fresh water areas with the purpose of gathering up bottom sediments and disposing of them at a different location. This technique is often used to keep waterways navigable.

It is also used as a way to replenish sand on some public beaches, where sand has been lost because of coastal erosion. Dredging is also used as a technique for fishing for certain species of edible clams and crabs, see fishing dredge.

A dredger (or “dredge” as is the general usage in the Americas) is any device, machine, or vessel that is used to excavate and remove material from the bottom of a body of water. For example, a scoop attached to the end of a rope or pole by which an operator can draw sediments up from the bottom of a pond is a dredger. Developing this idea further, a motorized crane equipped with a drag bucket or clamshell (grabber) that is used to scoop material from the bottom of a body of water is also a dredger. The crane could be located on the bank, or perhaps mounted on a barge. If the crane is mounted on a barge, the entire vessel is referred to as a dredger.[1]

The process of dredging creates spoils (excess material), which are carried away from the dredged area. Dredging can produce materials for land reclamation or other purposes (usually construction-related), and has also historically played a significant role in gold mining. Dredging can create disturbance in aquatic ecosystems, often with adverse impacts.

Types of dredging vessels

Suction

The Geopotes 14 lifting its boom on a canal in The Netherlands. (gēopotēs is Greek for "that which

drinks earth")

For suction-type excavation out of water, see Suction excavator.

These operate by sucking through a long tube, like some vacuum cleaners but on a larger scale.

A plain suction dredger has no tool at the end of the suction pipe to disturb the material. This is often the most commonly used form of dredging.[citation needed]



Trailing suction

A trailing suction hopper dredger (TSHD) trails its suction pipe when working. The pipe, which is fitted with a dredge drag head, loads the dredge spoil into one or more hoppers in the vessel. When the hoppers are full, the TSHD sails to a disposal area and either dumps the material through doors in the hull or pumps the material out of the hoppers. Some dredges also self-offload using drag buckets and conveyors.

The largest trailing suction hopper dredgers in the world are currently Jan De Nul's Cristobal Colon (launched 4 July 2008[2]) and its sister ship Leiv Eriksson (launched 4 September 2009[3]). Main design specs for the Cristobal Colon and the Leiv Eriksson are: 46,000 cubic metre hopper and a design dredging depth of 155 m.[4] Next largest is HAM 318 (Van Oord) with its 37,293 cubic metre hopper and a maximum dredging depth of 101 m.

Cutter-suction

A cutter-suction dredger's (CSD) suction tube has a cutting mechanism at the suction inlet. The cutting mechanism loosens the bed material and transports it to the suction mouth. The dredged material is usually sucked up by a wear-resistant centrifugal pump and discharged either through a pipe line or to a barge. Cutter-suction dredgers are most often used in geological areas consisting of hard surface materials (for example gravel deposits or surface bedrock) where a standard suction dredger would be ineffective. In recent years, dredgers with more powerful cutters have been built in order to excavate harder rock without the need for blasting.

The two largest cutter suction dredgers in the world are currently (as at August 2009) DEME's D'Artagnan (28,200 kW total installed power)[5] and Jan De Nul's J.F.J. DeNul (27,240 kW).[6] both built by IHC Merwede.

Auger suction

This process functions like a cutter suction dredger, but the cutting tool is a rotating Archimedean screw set at right angles to the suction pipe. The first widely used auger dredges were designed in the 1980s by Mud Cat Dredges, which was run by National Car Rental, but is now a Division of Ellicott Dredges. In 1996, IMS Dredges introduced a self-propelled version of the auger dredge that allows the system to propel itself without the use of anchors or cables. During the 1980s and 1990s auger dredges were primarily used for sludge removal applications from waste water treatment plants. Today, auger dredges are used for a wider variety of applications including river maintenance and sand mining.

The most common auger dredge on the global market today is the Versi-Dredge. The turbidity shroud on auger dredge systems creates a strong suction vacuum, causing much less turbidity than conical (basket) type cutterheads and so they are preferred for environmental applications. The vacuum created by the shroud and the ability to convey material to the pump faster makes auger dredge systems more productive than similar sized conical (basket) type cutterhead dredges.



Jet-lift

These use the Venturi effect of a concentrated highwater, together with bed mater

Air-lift

An airlift is a type of small suction dredge. It is sometimes used like other dredges. At other times, an airlift is handheld underwater by a and that air, being lighter than water, rises inside the pipe, dragging water with it.

Bucket

Bucket dredging

A bucket dredger is equipped with a bucket dredge, which is a device by mechanical means, often with many circulating buckets attached to a wheel or Some bucket dredgers and grab dredgers are powerful enough to rip out coral to make a shipping channel through coral reefs

Clamshell

Clamshell dredging in process in

A grab dredger picks up seabed material with a clam shell bucket, which hangs from an onboard crane or a crane barge



of a concentrated high-speed stream of water to pull the nearby water, together with bed material, into a pipe.

is a type of small suction dredge. It is sometimes used like other dredges. At other ld underwater by a diver.[7] It works by blowing air into the pipe,

hter than water, rises inside the pipe, dragging water with it.

dredger is equipped with a bucket dredge, which is a device that picks up by mechanical means, often with many circulating buckets attached to a wheel or Some bucket dredgers and grab dredgers are powerful enough to rip out coral to make a

coral reefs.

in Port Canaveral, Florida

dredger picks up seabed material with a clam shell bucket, which hangs from an crane barge, or is carried by a hydraulic arm, or is mounted like on a

speed stream of water to pull the nearby

is a type of small suction dredge. It is sometimes used like other dredges. At other It works by blowing air into the pipe,

hter than water, rises inside the pipe, dragging water with it.

that picks up sediment by mechanical means, often with many circulating buckets attached to a wheel or chain. Some bucket dredgers and grab dredgers are powerful enough to rip out coral to make a

dredger picks up seabed material with a clam shell bucket, which hangs from an , or is carried by a hydraulic arm, or is mounted like on a



dragline. This technique is often used in excavation of bay mud. Most of these dredges are crane barges with spuds.

Backhoe/dipper

A backhoe/dipper dredge has a backhoe like on some excavators. A crude but usable backhoe dredger can be made by mounting a land-type backhoe excavator on a pontoon. The six largest backhoe dredgers in the world are currently the Vitruvius, the Mimar Sinan, Postnik Jakovlev (Jan De Nul), the Samson (DEME), the Simson and the Goliath (Van Oord).[citation

needed] They featured barge-mounted excavators. Small backhoe dredgers can be track-mounted and work from the bank of ditches. A backhoe dredger is equipped with a half-open shell. The shell is filled moving towards the machine. Usually dredges material is loaded in barges. This machine is mainly used in harbors and other shallow water.

Water injection

A water injection dredger uses a small jet to inject water under low pressure (to prevent the sediment from exploding into the surrounding waters) into the seabed to bring the sediment in suspension, which then becomes a turbidity current, which flows away down slope, is moved by a second burst of water from the WID or is carried away in natural currents. Water injection results in a lot of sediment in the water which makes measurement with most hydrographic equipment (for instance: singlebeam echosounders) difficult.

Pneumatic

These dredgers use a chamber with inlets, out of which the water is pumped with the inlets closed. It is usually suspended from a crane on land or from a small pontoon or barge. Its effectiveness depends on depth pressure.

Bed leveler

Steam dredger Bertha, built 1844, on a demonstration run in 1982

This is a bar or blade which is pulled over the seabed behind any suitable ship or boat. It has an effect similar to that of a bulldozer on land. The chain-operated steam dredger Bertha, built in 1844 to a design by Brunel and now the oldest operational steam vessel in Britain, was of this type.[8]

Krabbelaar



This is an early type of dredger which was formerly used in shallow water in the Netherlands. It was a flat-bottomed boat with spikes sticking out of its bottom. As tide current pulled the boat, the spikes scraped seabed material loose, and the tide current washed the material away, hopefully to deeper water. Krabbelaar is Dutch for "scratcher".

Snagboat

Main article: Snagboat

A snagboat is designed to remove big debris such as dead trees and parts of trees from rivers and canals.

Amphibious

Some of these are any of the above types of dredger, which can operate normally, or by extending legs, also known as spuds, so it stands on the seabed with its hull out of the water. Some forms can go on land.

Some of these are land-type backhoe excavators whose wheels are on long hinged legs so it can drive into shallow water and keep its cab out of water. Some of these may not have a floatable hull and, if so, cannot work in deep water.

• Oliver Evans (1755–1819) in 1804 invented an amphibious dredger which was America's first

steam-powered road vehicle.

Submersible

These are usually used to recover useful materials from the seabed. Many of them travel on continuous track. A unique variant[9] is intended to walk on legs on the seabed.[10]

Fishing



Dredge haul including live clams and empty shells

Fishing dredges are used to collect various species of clams scallops, oysters or crabs from the seabed. These dredges have the form of a scoop made of chain mesh, and are towed by a fishing boat. Careless dredging can be destructive to the seabed. Nowadays some scallop dredging is replaced by collecting via scuba diving.[11]

Police drag

In some police departments a small dredge (sometimes called a drag) is used to find and recover objects and bodies from underwater. The bodies may be murder victims, or people who committed suicide by drowning, or victims of accidents. It is sometimes pulled by people walking on the bank. Search and rescue units also often use this type of dredge in searching for bodies of missing persons.

Disposal of materials

In a "hopper dredger", the dredged materials end up in a large onboard hold called a "hopper." A suction hopper dredger is usually used for maintenance dredging. A hopper dredge usually has doors in its bottom to empty the dredged materials, but some dredges empty their hoppers by splitting the two halves of their hulls on giant hydraulic hinges. Either way, as the vessel dredges, excess water in the dredged materials is spilled off as the heavier solids settle to the bottom of the hopper. This excess water is returned to the sea to reduce weight and increase the amount of solid material (or slurry) that can be carried in one load. When the hopper is filled with slurry, the dredger stops dredging and goes to a dump site and empties its hopper.

Some hopper dredges are designed so they can also be emptied from above using pumps if dump sites are unavailable or if the dredge material is contaminated. Sometimes the slurry of dredgings and water is pumped straight into pipes which deposit it on nearby land. Other times, it is pumped into barges (also called scows), which deposit it elsewhere while the dredge continues its work.

A number of vessels, notably in the UK and NW Europe de-water the hopper to dry the cargo to enable it to be discharged onto a quayside 'dry'. This is achieved principally using self discharge bucket wheel, drag scraper or excavator via conveyor systems.

When contaminated (toxic) sediments are to be removed, or large volume inland disposal sites are unavailable, dredge slurries are reduced to dry solids via a process known as dewatering. Current dewatering techniques employ either centrifuges, Geotube containers, large textile based filters or polymer flocculant/congealant based apparatus.

In many projects, slurry dewatering is performed in large inland settling pits, although this is becoming less and less common as mechanical dewatering techniques continue to improve.

Similarly, many groups (most notable in east Asia) are performing research towards utilizing dewatered sediments for the production of concretes and construction block, although the high organic content (in many cases) of this material is a hindrance toward such ends.



Environmental impacts

Dredging can create disturbance to aquatic ecosystems, often with adverse impacts. In addition, dredge spoils may contain toxic chemicals that may have an adverse effect on the disposal area; furthermore, the process of dredging often dislodges chemicals residing in benthic substrates and injects them into the water column.

The activity of dredging can create the following principal impacts to the environment:

• Release of toxic chemicals (including heavy metals and PCB) from bottom sediments into the

water column.

• Collection of heavy metals lead left by fishing, bullets, 98% mercury reclaimed [natural

occurring and left over from gold rush era].

• Short term increases in turbidity, which can affect aquatic species metabolism and interfere

with spawning suction dredging activity is allowed only during non-spawing time frames set

by fish and game (in-water work periods).

• Secondary impacts to marsh productivity from sedimentation

• Tertiary impacts to avifauna which may prey upon contaminated aquatic organisms

• Secondary impacts to aquatic and benthic organisms' metabolism and mortality

• Possible contamination of dredge spoils sites

• Changes to the topography by the creation of "spoil islands" from the accumulated spoil

• Releases toxic compound Tributyltin, a popular biocide used in anti-fouling paint banned in

2008, back into the water.

The nature of dredging operations and possible environmental impacts cause the industry to be closely regulated and a requirement for comprehensive regional environmental impact assessments with continuous monitoring. The U.S. Clean Water Act requires that any discharge of dredged or fill materials into "waters of the United States," including wetlands, is forbidden unless authorized by a permit issued by the Army Corps of Engineers.[12] As a result of the potential impacts to the environment, dredging is restricted to licenced areas only with vessel activity monitored closely using automatic GPS systems.

Major dredging companies

According to Reuters in 2010, the first and second largest dredging companies in the world respectively are Royal Boskalis Westminster of the Netherlands and China Harbour Engineering, a subsidiary of China Communications Construction.[13] Other large dredging companies in decreasing capacity order include:

• Van Oord Dredging and Marine Contractors (Netherlands)

• DEME (Belgium)

• Jan De Nul (Belgium)

Images



•

Grab dredge in the Port of Oakland, with San Francisco in the background

•

The 'business end' (excavator) of a Yukon dredge.

•

Profile view of this Yukon dredge tied up to a quay, note the size. The dredge conveys the spoils to the rear (left side) into a receiving vessel such as a barge.

•

April Hamer at Lakes Entrance, Victoria



•

Example of a trailing suction dredger: the Orisant in the port of IJmuiden, Netherlands

•

Grab dredging in Victoria Harbour, Hong Kong

•

Stuyvesant

•

Essayons



•

Alexander von Humboldt of the Jan de Nul fleet

•

Sand mining

•

HR Morris of the Manson Construction fleet, a Cutter Suction Pipeline Dredge, working on Mission Bay, San Diego, CA, USA

•

Dredge ship with barges on Neva bay in Saint Petersburg, Russia



•

Top view of a suction dredger on the Nandu River, Hainan, China

Dredge monitoring software

Dredgers are often equipped with dredge monitoring software to help the dredge operator position the dredger and monitor the current dredge level. The monitoring software often uses Real Time Kinematic satellite navigation to accurately record where the machine has been operating and to what depth the machine has dredged to.

reakwater (structure)


Breakwaters create safer harbours, but can also trap sediment moving along the coast. Alamitos Bay,

CA entrance channel.

Breakwaters are structures constructed on coasts as part of coastal defense or to protect an anchorage from the effects of both weather and longshore drift.

Purposes of breakwaters

Breakwaters, also called bulkheads, reduce the intensity of wave action in inshore waters and thereby reduce coastal erosion or provide safe harbourage. Breakwaters may also be small structures designed to protect a gently sloping beach and placed one to three hundred feet offshore in relatively shallow water.



An anchorage is only safe if ships anchored there are protected from the force of high winds and powerful waves by some large underwater barrier which they can shelter behind. Natural harbours are formed by such barriers as headlands or reefs. Artificial harbors can be created with the help of breakwaters. Mobile harbours, such as the D-Day Mulberry harbours, were floated into position and acted as breakwaters. Some natural harbours, such as those in Plymouth Sound, Portland Harbour and Cherbourg, have been enhanced or extended by breakwaters made of rock.

Unintended consequences

The dissipation of energy and relative calm water created in the lee of the breakwaters often encourage accretion of sediment (as per the design of the breakwater scheme). However this can lead to excessive salient build up, leading to tombolo formation reducing longshore drift shoreward of the breakwaters (Sea Palling, UK). This trapping of sediment can cause adverse effects down drift of the breakwaters leading to beach sediment starvation and increased erosion. This may then lead to further engineering protection being needed down drift of the breakwater development.

Breakwaters are subject to damage, and overtopping in severe storms events.

Three of the four breakwaters forming Portland Harbour

The eight offshore breakwaters at Elmer, UK

Construction

Breakwaters can be constructed with one end linked to the shore, in which case they are usually classified as sea walls; otherwise they are positioned offshore from as little as 100 m up to 300-600 m from the original shoreline. There are two main types of offshore breakwater, single and multiple; single as the name suggests means the breakwater consists of one unbroken barrier, which multiple breakwaters (in numbers anywhere from 2-20) are positioned with gaps in between (50-300 m). Length of gap is largely governed by the interacting wavelengths. Breakwaters may be either fixed or floating, and impermeable or



permeable to allow sediment transfer shoreward of the structures, the choice depending tidal range and water depth. They usually consist of large pieces of rock (granite) weighing up to 16 tonnes each, or rubble-mound. Their design is influenced by the angle of wave approach and other environmental parameters. Breakwater construction can be either parallel or perpendicular to the coast, depending on the shoreline requirements.

Types of breakwater structures

A breakwater structure is designed to absorb the energy of the waves that hit it, either by using mass (e.g., with caissons), or by using a revetment slope (e.g., with rock or concrete armour units).

In coastal engineering, a revetment is a land backed structure whilst a breakwater is a sea backed structure (i.e., water on both sides).

Caisson breakwaters typically have vertical sides and are usually erected where it is desirable to berth one or more vessels on the inner face of the breakwater. They use the mass of the caisson and the fill within it to resist the overturning forces applied by waves hitting them. They are relatively expensive to construct in shallow water, but in deeper sites they can offer a significant saving over revetment breakwaters.

Rubble mound breakwaters use structural voids to dissipate the wave energy. Rock or concrete armour units on the outside of the structure absorb most of the energy, while gravels or sands prevent the wave energy's continuing through the breakwater core. The slopes of the revetment are typically between 1:1 and 1:2, depending upon the materials used. In shallow water, revetment breakwaters are usually relatively inexpensive. As water depth increases, the material requirements, and hence costs, increase significantly.[citation needed]

Advanced numerical study



3D Numerical Simulation - MEDUS 2009

The Maritime Engineering Division of the University of Salerno (MEDUS) developed a new procedure for studying in greater detail the interactions between maritime breakwaters (submerged or emerged) and the waves that hit them by making integrated use of CAD and CFD software.

In the numerical simulations, the filtration motion of the fluid within the interstices, which normally exist in a breakwater, is estimated by integrating the RANS equations, coupled with a RNG turbulence model inside the voids, instead of using classical equations for porous media.

The breakwaters were modelled, in analogy to full size construction or physical laboratory tests, by overlapping three-dimensional elements and having the numerical grid thickened in order to have some computational nodes along the flow paths among the breakwater’s blocks.

Notable locations

• UK - Sea Palling, Norfolk; Elmer, West Sussex • USA - Santa Monica, California; Winthrop Beach, Massachusetts; Colonial Beach,

Virginia • Japan - Central Breakwater in Tokyo; Ishizaki (檜山石崎郵便局), Hokkaido

Prefecture; Kaike, Tottori Prefecture

Airy wave theory From Wikipedia, the free encyclopedia

In fluid dynamics, Airy wave theory (often referred to as linear wave theory) gives a linearised description of the propagation of gravity waves on the surface of a homogeneous fluid layer. The theory assumes that the fluid layer has a uniform mean depth, and that the fluid flow is inviscid, incompressible and irrotational. This theory was first published, in correct form, by George Biddell Airy in the 19th century.[1]

Airy wave theory is often applied in ocean engineering and coastal engineering for the modelling of random sea states – giving a description of the wave kinematics and dynamics of high-enough accuracy for many purposes.[2] [3] Further, several second-order nonlinear properties of surface gravity waves, and their propagation, can be estimated from its results.[4] Airy wave theory is also a good approximation for tsunami waves in the ocean, before they steepen near the coast.



This linear theory is often used to get a quick and rough estimate of wtheir effects. This approximation is accurate for small ratios of the (for waves in shallow water), and wave height to wavelength (for waves in deep water).

Description

Wave characteristics.

Dispersion of gravity waves on a fluid surface. a function of h/λ. A: phase velocity, valid in shallow water. Drawn linesDashed lines: based on dispersion relation valid in deep water.

Airy wave theory uses a potential flowof gravity waves on a fluid surface. The use of water waves is remarkably successful, given its failure to describe many other fluid flows where it is often essential to take account. This is due to the fact that for the oscillatory part of the fluid motion, wavevorticity is restricted to some thin oscillatory fluid domain.[5]

Airy wave theory is often used in random waves, sometimes called including the wave spectrum –wavelengths) and in not too shallow water. be described with Airy wave theory. Further, by using the shoaling and refraction can be predicted.

Earlier attempts to describe surface gravity waves usothers, Laplace, Poisson, Cauchyderivation and formulation in 1841.extended by Stokes for non-linearto third order in the wave steepness.nonlinear trochoidal wave theory in 1804, which however is not

Airy wave theory is a linear theory for the propagation of waves on the surface of a potential flow and above a horizontal bottom. The free surface elevation is sinusoidal, as a function of horizontal position



This linear theory is often used to get a quick and rough estimate of wave characteristics and their effects. This approximation is accurate for small ratios of the wave height

), and wave height to wavelength (for waves in deep water).

Dispersion of gravity waves on a fluid surface. Phase and group velocity divided by

: phase velocity, B: group velocity, C: phase and group velocity Drawn lines: based on dispersion relation valid in arbitrary depth.

: based on dispersion relation valid in deep water.

potential flow (or velocity potential) approach to describe the of gravity waves on a fluid surface. The use of – inviscid and irrotational –water waves is remarkably successful, given its failure to describe many other fluid flows where it is often essential to take viscosity, vorticity, turbulence and/or flow separationaccount. This is due to the fact that for the oscillatory part of the fluid motion, wavevorticity is restricted to some thin oscillatory Stokes boundary layers at the boundaries of the

Airy wave theory is often used in ocean engineering and coastal engineeringwaves, sometimes called wave turbulence, the evolution of the wave statistics

– is predicted well over not too long distances (in terms of wavelengths) and in not too shallow water. Diffraction is one of the wave effects wbe described with Airy wave theory. Further, by using the WKBJ approximation

can be predicted.[2]

Earlier attempts to describe surface gravity waves using potential flow were made by, among Cauchy and Kelland. But Airy was the first to publish the correct

derivation and formulation in 1841.[1] Soon after, in 1847, the linear theory of Airy was linear wave motion – known as Stokes' wave theory

in the wave steepness.[6] Even before Airy's linear theory, Gerstnerwave theory in 1804, which however is not irrotational

Airy wave theory is a linear theory for the propagation of waves on the surface of a potential flow and above a horizontal bottom. The free surface elevation η(x,t) of one wave component

, as a function of horizontal position x and time t:

ave characteristics and wave height to water depth

), and wave height to wavelength (for waves in deep water).

divided by √(gh) as : phase and group velocity √(gh)

: based on dispersion relation valid in arbitrary depth.

) approach to describe the motion – potential flow in

water waves is remarkably successful, given its failure to describe many other fluid flows flow separation into

account. This is due to the fact that for the oscillatory part of the fluid motion, wave-induced at the boundaries of the

coastal engineering. Especially for , the evolution of the wave statistics –

is predicted well over not too long distances (in terms of is one of the wave effects which can

WKBJ approximation, wave

ing potential flow were made by, among was the first to publish the correct

Soon after, in 1847, the linear theory of Airy was Stokes' wave theory – correct up

Gerstner derived a irrotational.[1]

Airy wave theory is a linear theory for the propagation of waves on the surface of a potential ) of one wave component



where

• a is the wave amplitude• cos is the cosine function,• k is the angular wavenumber

• ω is the angular frequencyf by

The waves propagate along the water surface with the

The angular wavenumber k and frequency wavelength λ and period T are not independent), but are coupled. Surface gravity waves on a fluid are dispersive waves – exhibiting frequency dispersion wavenumber has its own frequency and phase speed.

Note that in engineering the wave heighttrough – is often used:

valid in the present case of linear periodic waves.

Orbital motion under linear waves. The yellow dots indicate the momentary position of fluid particles on their (orange) orbits. The black dots are the centres of the orbits.

Underneath the surface, there is a fluid motion associatthe surface elevation shows a propagating wave, the fluid particles are in an Within the framework of Airy wave theory, the orbits are closwater, and ellipses in finite depthfluid layer. So while the wave propagates, the fluid particles just orbit (oscillate) around their average position. With the propagating wave motion, the fluid particles transfer energy in the



amplitude in metre, function,

angular wavenumber in radian per metre, related to the wavelength

angular frequency in radian per second, related to the period

The waves propagate along the water surface with the phase speed cp:

and frequency ω are not independent parameters (and thus also are not independent), but are coupled. Surface gravity waves on a

exhibiting frequency dispersion – meaning that each wavenumber has its own frequency and phase speed.

wave height H – the difference in elevation between

linear periodic waves.


Underneath the surface, there is a fluid motion associated with the free surface motion. While the surface elevation shows a propagating wave, the fluid particles are in an Within the framework of Airy wave theory, the orbits are closed curves: circles in deep water, and ellipses in finite depth—with the ellipses becoming flatter near the bottom of the fluid layer. So while the wave propagates, the fluid particles just orbit (oscillate) around their

position. With the propagating wave motion, the fluid particles transfer energy in the

wavelength λ as

period T and frequency

are not independent parameters (and thus also are not independent), but are coupled. Surface gravity waves on a

meaning that each

elevation between crest and


ed with the free surface motion. While the surface elevation shows a propagating wave, the fluid particles are in an orbital motion.

ed curves: circles in deep with the ellipses becoming flatter near the bottom of the

fluid layer. So while the wave propagates, the fluid particles just orbit (oscillate) around their position. With the propagating wave motion, the fluid particles transfer energy in the



wave propagation direction, without having a mean velocity. The diameter of the orbits reduces with depth below the free surface. I4% of its free-surface value at a depth of half a wavelength.

In a similar fashion, there is also a pressure oscillation underneath the free surface, with wave-induced pressure oscillations reducing with depway as for the orbital motion of fluid parcels.

Mathematical formulation of the wave motion

Flow problem formulation

The waves propagate in the horizontal direction, with above by a free surface at z = direction) and t being time.[7] The level The impermeable bed underneath the fluid layer is at be incompressible and irrotationalwaves on a liquid surface – and velocity potential Φ(x,z,t) is related to the horizontal (x) and vertical (z) directions by:

Then, due to the continuity equationthe Laplace equation:

Boundary conditions are needed at the bed and the free surface in order to close the system of equations. For their formulation within the framework of linear theory, it specify what the base state (or state is rest, implying the mean flow velocities are z

The bed being impermeable, leads to the

In case of deep water – by which is meant view – the flow velocities have to go to zero in the minus infinity: z → -∞.

At the free surface, for infinitesimalthe vertical velocity of the free surface. This leads to the kinemacondition:



wave propagation direction, without having a mean velocity. The diameter of the orbits reduces with depth below the free surface. In deep water, the orbit's diameter is reduced to

surface value at a depth of half a wavelength.

In a similar fashion, there is also a pressure oscillation underneath the free surface, with induced pressure oscillations reducing with depth below the free surface

way as for the orbital motion of fluid parcels.

Mathematical formulation of the wave motion

Flow problem formulation

The waves propagate in the horizontal direction, with coordinate x, and a fluid domain bound = η(x,t), with z the vertical coordinate (positive in the upward

The level z = 0 corresponds with the mean surface elevation. erneath the fluid layer is at z = -h. Further, the flow is assumed to

irrotational – a good approximation of the flow in the fluid interior for and potential theory can be used to describe the flow. The

) is related to the flow velocity components ux and ) directions by:

continuity equation for an incompressible flow, the potential

are needed at the bed and the free surface in order to close the system of equations. For their formulation within the framework of linear theory, it is necessary to specify what the base state (or zeroth-order solution) of the flow is. Here, we assume the base state is rest, implying the mean flow velocities are zero.

The bed being impermeable, leads to the kinematic bed boundary-condition:

by which is meant infinite water depth, from a mathematical point of the flow velocities have to go to zero in the limit as the vertical coordinate goes to

infinitesimal waves, the vertical motion of the flow has to be equal to the vertical velocity of the free surface. This leads to the kinematic free-surface boundary

wave propagation direction, without having a mean velocity. The diameter of the orbits n deep water, the orbit's diameter is reduced to

In a similar fashion, there is also a pressure oscillation underneath the free surface, with th below the free surface – in the same

, and a fluid domain bound the vertical coordinate (positive in the upward 0 corresponds with the mean surface elevation.

. Further, the flow is assumed to a good approximation of the flow in the fluid interior for

can be used to describe the flow. The and uz in the

for an incompressible flow, the potential Φ has to satisfy

are needed at the bed and the free surface in order to close the system of is necessary to

) of the flow is. Here, we assume the base

condition:

water depth, from a mathematical point of as the vertical coordinate goes to

waves, the vertical motion of the flow has to be equal to surface boundary-



If the free surface elevation η(flow problem. However, the surface elevation is an extra unknown, for which an additional boundary condition is needed. Thispotential flow. The pressure above the free surface is assumed to be constant.pressure is taken equal to zero, without loss of generality, since the level of such a constant pressure does not alter the flow. After linearisation, this gives the boundary condition:

Because this is a linear theory, in both freethe dynamic one, equations (3) and (4) z = 0 is used.

Solution for a progressive monochromatic wave

See also: Dispersion (water waves)

For a propagating wave of a single frequency elevation is of the form:[7]

The associated velocity potential, satisfyingwell as the kinematic boundary conditions at the free surface (2), and bed (3), is:

with sinh and cosh the hyperbolic sinand Φ also have to satisfy the dynamic boundary condition, which results in nonzero) values for the wave amplitude

with tanh the hyperbolic tangentequivalently period T and wavelength This means that wave propagation at a fluid surface is an satisfy the dispersion relation, the wave amplitude for Airy wave theory to be a valid approximation).

Table of wave quantities



(x,t) was a known function, this would be enough to solve the flow problem. However, the surface elevation is an extra unknown, for which an additional boundary condition is needed. This is provided by Bernoulli's equation for an unsteady potential flow. The pressure above the free surface is assumed to be constant.pressure is taken equal to zero, without loss of generality, since the level of such a constant pressure does not alter the flow. After linearisation, this gives the dynamic

Because this is a linear theory, in both free-surface boundary conditions – the kinematic and the dynamic one, equations (3) and (4) – the value of Φ and ∂Φ/∂z at the fixed mean level

Solution for a progressive monochromatic wave

Dispersion (water waves)

For a propagating wave of a single frequency – a monochromatic wave – the surface

The associated velocity potential, satisfying the Laplace equation (1) in the fluid interior, as well as the kinematic boundary conditions at the free surface (2), and bed (3), is:

hyperbolic sine and hyperbolic cosine function, respectively. But also have to satisfy the dynamic boundary condition, which results in non

zero) values for the wave amplitude a only if the linear dispersion relation

hyperbolic tangent. So angular frequency ω and wavenumber and wavelength λ – cannot be chosen independently, but are related.

This means that wave propagation at a fluid surface is an eigenproblem. When satisfy the dispersion relation, the wave amplitude a can be chosen freely (but small enough for Airy wave theory to be a valid approximation).

) was a known function, this would be enough to solve the flow problem. However, the surface elevation is an extra unknown, for which an additional

for an unsteady potential flow. The pressure above the free surface is assumed to be constant. This constant pressure is taken equal to zero, without loss of generality, since the level of such a constant

free-surface

the kinematic and at the fixed mean level

the surface

the Laplace equation (1) in the fluid interior, as well as the kinematic boundary conditions at the free surface (2), and bed (3), is:

function, respectively. But η also have to satisfy the dynamic boundary condition, which results in non-trivial (non-

is satisfied:

and wavenumber k – or osen independently, but are related.

. When ω and k be chosen freely (but small enough



In the table below, several flow quantities and parameters according to Airy wave theory are given.[7] The given quantities are for a bit more general situation as for the solution given above. Firstly, the waves may propagate in an arbitrary horizontal direction in the plane. The wavenumber vector is Secondly, allowance is made for a mean flouniform over (independent of) depth relations. At an Earth-fixed location, the frequency) is ω. On the other hand, in a (so the mean velocity as observed from this reference frame is zero), the angular frequency is different. It is called the intrinsic angular frequencyas σ. So in pure wave motion, with number k (and wavelength λ) are independent of the shift (for monochromatic waves).

The table only gives the oscillatory parts of flow and pressure – and not their mean value or drift. The oscillatory particle excursions are the time integrals of the oscillatory flow

Water depth is classified into three regimes:

• deep water – for a water depth larger than half the speed of the waves is hardly influenced by depth (this is the case for most wind waves on the sea and ocean surface),

• shallow water – for a water depth smaller than the wavelength divided by 20, λ, the phase speed of the waves is only dependent on water depth, and no longer a function of period or wavelength;

• intermediate depth – period (or wavelength)theory.

In the limiting cases of deep and shallow water, simplifying approximations to the solution can be made. While for intermediate depth, the full formulations have to be used.

Properties of gravity waves on the surface of deep water, shallow water and at

intermediate depth, according to Airy wave theory

quantity symbol uni

ts

deep water

surface

elevation

m

wave

phase

rad



In the table below, several flow quantities and parameters according to Airy wave theory are The given quantities are for a bit more general situation as for the solution given

above. Firstly, the waves may propagate in an arbitrary horizontal direction in the vector is k, and is perpendicular to the cams of the

Secondly, allowance is made for a mean flow velocity U, in the horizontal direction and uniform over (independent of) depth z. This introduces a Doppler shift in the dispersion

fixed location, the observed angular frequency (or absolute angular . On the other hand, in a frame of reference moving with the mean velocity

erved from this reference frame is zero), the angular frequency is intrinsic angular frequency (or relative angular frequency

. So in pure wave motion, with U=0, both frequencies ω and σ are equal. The wave ) are independent of the frame of reference, and have no Doppler

shift (for monochromatic waves).

The table only gives the oscillatory parts of flow quantities – velocities, particle excursions and not their mean value or drift. The oscillatory particle excursions

of the oscillatory flow velocities ux and uz respectively.

Water depth is classified into three regimes:[8]

for a water depth larger than half the wavelength, h > ½ of the waves is hardly influenced by depth (this is the case for most wind waves

on the sea and ocean surface),[9] for a water depth smaller than the wavelength divided by 20,

, the phase speed of the waves is only dependent on water depth, and no longer a or wavelength;[10] and

all other cases, 1⁄20 λ < h < ½ λ, where both water depth and period (or wavelength) have a significant influence on the solution of Airy wave


ravity waves on the surface of deep water, shallow water and at

intermediate depth, according to Airy wave theory[7]

deep water

( h > ½ λ )

shallow water

( h < 0.05 λ )

intermediate depth

( all

In the table below, several flow quantities and parameters according to Airy wave theory are The given quantities are for a bit more general situation as for the solution given

above. Firstly, the waves may propagate in an arbitrary horizontal direction in the x = (x,y) , and is perpendicular to the cams of the wave crests.

, in the horizontal direction and in the dispersion

absolute angular moving with the mean velocity U

erved from this reference frame is zero), the angular frequency is relative angular frequency), denoted

are equal. The wave , and have no Doppler

velocities, particle excursions and not their mean value or drift. The oscillatory particle excursions ξx and ξz

respectively.

> ½ λ, the phase of the waves is hardly influenced by depth (this is the case for most wind waves

for a water depth smaller than the wavelength divided by 20, h < 1⁄20 , the phase speed of the waves is only dependent on water depth, and no longer a

, where both water depth and have a significant influence on the solution of Airy wave


ravity waves on the surface of deep water, shallow water and at [7]

intermediate depth

( all λ and h )



observed

angular

frequenc

y

rad / s

intrinsic

angular

frequenc

y

rad / s

unit

vector in

the wave

propagat

ion

direction

–

dispersio

n

relation

rad / s

phase

speed

m / s

group

speed

m / s

ratio

–

horizont

al

velocity

m / s

vertical

velocity

m / s

horizont

al

particle

excursio

n

m





vertical

particle

excursio

n

m

pressure

oscillatio

n

N / m2

Surface tension effects

Main article: Capillary wave

Dispersion of gravity–capillary waves on the surface of deep water. Phase and group velocity

divided by as a function of inverse relative wavelength Blue lines (A): phase velocity Drawn lines: gravity–capillary waves.Dashed lines: gravity waves. Dash-dot lines: pure capillary waves.

Due to surface tension, the dispersion relation changes to:

with γ the surface tension, with the same, if the gravitational accelera

As a result of surface tension, the waves propagate faster. Surface tension only has influence for short waves, with wavelengths less than a few For very short wavelengths – two millimeter in case of the interface between air and water gravity effects are negligible.

The group velocity ∂Ω/∂k of capillary waves greater than the phase velocity(with surface tension negligible compared to the effects of gravity) where the phase velocity exceeds the group velocity.[13]



Surface tension effects

capillary waves on the surface of deep water. Phase and group velocity

as a function of inverse relative wavelength .Blue lines (A): phase velocity cp, Red lines (B): group velocity cg.

apillary waves.

dot lines: pure capillary waves.

, the dispersion relation changes to:[11]

the surface tension, with SI units in N/m. All above equations for linear waves remain the same, if the gravitational acceleration g is replaced by[12]

As a result of surface tension, the waves propagate faster. Surface tension only has influence for short waves, with wavelengths less than a few decimeters in case of a water

two millimeter in case of the interface between air and water

of capillary waves – dominated by surface tension effects ity Ω/k. This is opposite to the situation of surface gravity waves

(with surface tension negligible compared to the effects of gravity) where the phase velocity [13]

capillary waves on the surface of deep water. Phase and group velocity

.

units in N/m. All above equations for linear waves remain

As a result of surface tension, the waves propagate faster. Surface tension only has influence in case of a water–air interface.

two millimeter in case of the interface between air and water –

dominated by surface tension effects – is . This is opposite to the situation of surface gravity waves

(with surface tension negligible compared to the effects of gravity) where the phase velocity



Interfacial waves

Surface waves are a special case of interfacial waves, on the different density.

Two layers of infinite depth

Consider two fluids separated by an interface, and without further boundaries. Then their dispersion relation ω2 = Ω2(k) is given through:

where ρ and ρ‘ are the densities of the two fluids, below (respectively. Further γ is the surface tension on the interface.

For interfacial waves to exist, the lower layer has to be heOtherwise, the interface is unstable and a

Two layers between horizont

Wave motion on the interface between two layers of density, confined between horizontal rigid boundaries (at the top and bottomforced by gravity. The upper layer has mean depth has mean depth h and density (related to the wavenumber k by: speed as cp (with cp = Ω(k) / k).

For two homogeneous layers of fluids, of mean thickness – under the action of gravity and bounded above and below by horizontal rigid walls dispersion relationship ω2 = Ω

where again ρ and ρ′ are the densities below and above the interface, while coth is the hyperbolic cotangent function. For the case surface gravity waves on water of finite depth

Two layers bounded above by a free surface



Surface waves are a special case of interfacial waves, on the interface between two fluids of

Two layers of infinite depth

Consider two fluids separated by an interface, and without further boundaries. Then their ) is given through:[11][14][15]

are the densities of the two fluids, below (ρ) and above (ρ‘) the interface, is the surface tension on the interface.

For interfacial waves to exist, the lower layer has to be heavier than the upper one, Otherwise, the interface is unstable and a Rayleigh–Taylor instability develops.

Two layers between horizontal rigid planes

Wave motion on the interface between two layers of inviscid homogeneous fluids of different density, confined between horizontal rigid boundaries (at the top and bottomforced by gravity. The upper layer has mean depth h‘ and density ρ‘, while the lower layer

and density ρ. The wave amplitude is a, the wavelength is denoted by by: k = 2π / λ), the gravitational acceleration by ).

For two homogeneous layers of fluids, of mean thickness h below the interface and under the action of gravity and bounded above and below by horizontal rigid walls

Ω2(k) for gravity waves is provided by:[16]

are the densities below and above the interface, while coth is the function. For the case ρ′ is zero this reduces to the dispersion relation of

surface gravity waves on water of finite depth h.

Two layers bounded above by a free surface

between two fluids of

Consider two fluids separated by an interface, and without further boundaries. Then their

) the interface,

avier than the upper one, ρ > ρ‘. develops.

homogeneous fluids of different density, confined between horizontal rigid boundaries (at the top and bottom). The motion is

, while the lower layer , the wavelength is denoted by λ

), the gravitational acceleration by g and the phase

below the interface and h′ above under the action of gravity and bounded above and below by horizontal rigid walls – the

are the densities below and above the interface, while coth is the is zero this reduces to the dispersion relation of



In this case the dispersion relation allows for two modes: a surface amplitude is large compared with the amplitude of the interfacial wave, and a baroclinic mode where the opposite is the case antiphase with the free surface wave. The dispersion relation for this case is of a more complicated form.[17]

Second-order wave prop

Several second-order wave properties, directly from Airy wave theory. They are of importance in many practical applications, forecasts of wave conditions.[18]

also find their applications in describing waves in case of slowlmean-flow variations of currents and surface elevation. As well as in the description of the wave and mean-flow interactions due to time and spacewavelength and direction of the wave field itself.

Table of second-order wave properties

In the table below, several secondthey satisfy in case of slowly varying conditioon these can be found below. The table gives results for wave propagation in one horizontal spatial dimension. Further on in this section, more detailed descriptions and results are given for the general case of propagation in two

Second-order quantities and their dynamics, using results of Airy wave theory

quantity symb

ol units

mean

wave-

energy

density per

unit

horizontal

area

J / m2

radiation

stress or

excess

horizontal

momentu

m flux due

to the wave

motion

N / m

wave

action

J·s / m2



In this case the dispersion relation allows for two modes: a barotropic mode where the free large compared with the amplitude of the interfacial wave, and a

mode where the opposite is the case – the interfacial wave is higher than and in with the free surface wave. The dispersion relation for this case is of a more

order wave properties

wave properties, i.e. quadratic in the wave amplitude directly from Airy wave theory. They are of importance in many practical applications,

[18] Using a WKBJ approximation, second-order wave properties also find their applications in describing waves in case of slowly varying bathymetry

flow variations of currents and surface elevation. As well as in the description of the flow interactions due to time and space-variations in amplitude, frequency,

wavelength and direction of the wave field itself.

order wave properties

In the table below, several second-order wave properties – as well as the dynamical equations they satisfy in case of slowly varying conditions in space and time – are given. More details on these can be found below. The table gives results for wave propagation in one horizontal spatial dimension. Further on in this section, more detailed descriptions and results are given

of propagation in two-dimensional horizontal space.

order quantities and their dynamics, using results of Airy wave theory

formula

mode where the free large compared with the amplitude of the interfacial wave, and a

the interfacial wave is higher than and in with the free surface wave. The dispersion relation for this case is of a more

ude a, can be derived directly from Airy wave theory. They are of importance in many practical applications, e.g.

order wave properties bathymetry, and

flow variations of currents and surface elevation. As well as in the description of the in amplitude, frequency,

as well as the dynamical equations are given. More details

on these can be found below. The table gives results for wave propagation in one horizontal spatial dimension. Further on in this section, more detailed descriptions and results are given

order quantities and their dynamics, using results of Airy wave theory



mean

mass-flux

due to the

wave

motion or

the wave

pseudo-

momentu

m

kg / (m·s)

mean

horizontal

mass-

transport

velocity

m / s

Stokes

drift

m / s

wave-

energy

propagatio

n

J / (m2·s

)

wave

action

conservati

on

J / m2

wave-crest

conservati

on

rad / (m·s)

mean mass

conservati

on

kg / (m2·s

)

mean

horizontal-

momentu

m

evolution

N / m2

The last four equations describe the evolution of slowly varying wave trains over in interaction with the mean flowaverage Lagrangian method.[19]

water depth, i.e. the bed underneath the fluid layer is located at

flow velocity in the mass and momentum equations is the



with

ions describe the evolution of slowly varying wave trains over mean flow, and can be derived from a variational principle:

[19] In the mean horizontal-momentum equation, the bed underneath the fluid layer is located at z = –d. Note that the mean

ss and momentum equations is the mass transport velocity

ions describe the evolution of slowly varying wave trains over bathymetry an be derived from a variational principle: Whitham's

momentum equation, d(x) is the still . Note that the mean-

mass transport velocity ,



including the splash-zone effects of the waves on horizontal mass transport, and not the mean Eulerian velocity (e.g. as measured with a fixed flow meter).

Wave energy density

Wave energy is a quantity of primary interest, since it is a primary quantity that is transported with the wave trains.[20] As can be seen above, many wave quantities like surface elevation and orbital velocity are oscillatory in nature with zero mean (within the framework of linear theory). In water waves, the most used energy unit horizontal area. It is the sum of the the depth of the fluid layer and averaged over the wave phase. Simplest to derive is the mean potential energy density per unit horizontal area the deviation of the potential energy due to the presence of the waves:

with an overbar denoting the mean value (which in the present case of periodic waves can be taken either as a time average or an average over one wavelength in space).

The mean kinetic energy density per unit horizontal area found to be:[21]

with σ the intrinsic frequency, see the the result for surface gravity waves is:

As can be seen, the mean kinetic and potential energy densities are equal. This is a general property of energy densities of progressive linear waves in a Adding potential and kinetic contributions, horizontal area E of the wave motion is:

In case of surface tension effects not being negligible, their contribution also adds to the potential and kinetic energy densities, giving

with γ the surface tension.



zone effects of the waves on horizontal mass transport, and not the mean velocity (e.g. as measured with a fixed flow meter).

Wave energy is a quantity of primary interest, since it is a primary quantity that is transported As can be seen above, many wave quantities like surface elevation

and orbital velocity are oscillatory in nature with zero mean (within the framework of linear theory). In water waves, the most used energy measure is the mean wave energy density per unit horizontal area. It is the sum of the kinetic and potential energy density, integrated over the depth of the fluid layer and averaged over the wave phase. Simplest to derive is the mean potential energy density per unit horizontal area Epot of the surface gravity waves, which is

e potential energy due to the presence of the waves:[21]

with an overbar denoting the mean value (which in the present case of periodic waves can be as a time average or an average over one wavelength in space).

The mean kinetic energy density per unit horizontal area Ekin of the wave motion is similarly

the intrinsic frequency, see the table of wave quantities. Using the dispersion relation, the result for surface gravity waves is:

en, the mean kinetic and potential energy densities are equal. This is a general property of energy densities of progressive linear waves in a conservative systemAdding potential and kinetic contributions, Epot and Ekin, the mean energy den

of the wave motion is:

In case of surface tension effects not being negligible, their contribution also adds to the potential and kinetic energy densities, giving[22]

zone effects of the waves on horizontal mass transport, and not the mean

Wave energy is a quantity of primary interest, since it is a primary quantity that is transported As can be seen above, many wave quantities like surface elevation

and orbital velocity are oscillatory in nature with zero mean (within the framework of linear measure is the mean wave energy density per

density, integrated over the depth of the fluid layer and averaged over the wave phase. Simplest to derive is the mean

of the surface gravity waves, which is

with an overbar denoting the mean value (which in the present case of periodic waves can be as a time average or an average over one wavelength in space).

of the wave motion is similarly

. Using the dispersion relation,

en, the mean kinetic and potential energy densities are equal. This is a general conservative system.[22][23]

, the mean energy density per unit

In case of surface tension effects not being negligible, their contribution also adds to the



Wave action, wave energy flux and radiation stress

In general, there can be an energy transfer between the wave motion and the mean fluid motion. This means, that the wave energy density is not in all cases a conserved quantity (neglecting dissipative effects), but the total energy density per unit area of the wave motion and the mean flow motion varying wave trains, propagating in slowly varying

similar and conserved wave quantity, the

with the action conservation forms the basis for many is also the basis of coastal engineeringExpanding the above wave action conservation equation leads to the following evolution equation for the wave energy density:

with:

• is the mean wave energy density flux,• is the radiation stress• is the mean-velocity

In this equation in non-conservation form, the source term describing the energy exchange of the wave motion with the mean flow. Only in case the mean shear-rate is zero, The two tensors and are in a

with and the components of the wavenumber vector components in of the mean velocity vector



Wave action, wave energy flux and radiation stress

In general, there can be an energy transfer between the wave motion and the mean fluid means, that the wave energy density is not in all cases a conserved quantity

), but the total energy density – the sum of the energy density rea of the wave motion and the mean flow motion – is. However, there is for slowly

varying wave trains, propagating in slowly varying bathymetry and mean-flow fields, a

served wave quantity, the wave action [19][24][25]

the action flux and the group velocity vector. Action conservation forms the basis for many wind wave models and wave turbulence

coastal engineering models for the computation of wave shoalingExpanding the above wave action conservation equation leads to the following evolution equation for the wave energy density:[28]

is the mean wave energy density flux, radiation stress tensor and

velocity shear-rate tensor.

conservation form, the Frobenius inner product source term describing the energy exchange of the wave motion with the mean flow. Only in

rate is zero, the mean wave energy density are in a Cartesian coordinate system of the form:

the components of the wavenumber vector and similarly components in of the mean velocity vector .

In general, there can be an energy transfer between the wave motion and the mean fluid means, that the wave energy density is not in all cases a conserved quantity

the sum of the energy density is. However, there is for slowly

flow fields, a [25]

vector. Action wave turbulence models.[26] It

wave shoaling.[27] Expanding the above wave action conservation equation leads to the following evolution

is the source term describing the energy exchange of the wave motion with the mean flow. Only in

the mean wave energy density is conserved. of the form:[29]

and the



Wave mass flux and wave momentum

The mean horizontal momentumwave-induced mass flux or mass

which is an exact result for periodic progressive water waves, also valid for waves.[31] However, its validity strongly depends on the way how wave momentum and mass flux are defined. Stokes already identified two possible definitions of periodic nonlinear waves:[6]

• Stokes first definition of wave equal to zero for all elevations

• Stokes second definition of wave celerityzero.

The above relation between wave momentum the framework of Stokes' first definition.

However, for waves perpendicular to a coast line or in closed laboratory second definition (S2) is more appropriate. These wave systems have zero mass flux and momentum when using the second definition.definition (S1), there is a wavehas to be balanced by a mean flow

So in general, there are quite some subtleties involved. Therefore also the term pseudomomentum of the waves is used instead of wave momentum.

Mass and momentum evolution equations

For slowly varying bathymetry

can de described in terms of the mean mass

Note that for deep water, when the mean depth

and mean transport velocity

The equation for mass conservation is:

where h(x,t) is the mean waterhorizontal momentum evolves as:



Wave mass flux and wave momentum

momentum per unit area induced by the wave motion or mass transport – is:[30]

which is an exact result for periodic progressive water waves, also valid for However, its validity strongly depends on the way how wave momentum and mass

already identified two possible definitions of phase velocity

Stokes first definition of wave celerity (S1) – with the mean Eulerian flow velocityequal to zero for all elevations z below the wave troughs, and Stokes second definition of wave celerity (S2) – with the mean mass transport equal to

The above relation between wave momentum M and wave energy density Ethe framework of Stokes' first definition.

However, for waves perpendicular to a coast line or in closed laboratory wave channelsecond definition (S2) is more appropriate. These wave systems have zero mass flux and momentum when using the second definition.[32] In contrast, according to Stokes' first definition (S1), there is a wave-induced mass flux in the wave propagation direction, which has to be balanced by a mean flow U in the opposite direction – called the undertow

So in general, there are quite some subtleties involved. Therefore also the term pseudomomentum of the waves is used instead of wave momentum.[33]

Mass and momentum evolution equations

bathymetry, wave and mean-flow fields, the evolution of the mean flow

can de described in terms of the mean mass-transport velocity defined as:

Note that for deep water, when the mean depth h goes to infinity, the mean Eulerian velocity

and mean transport velocity become equal.

The equation for mass conservation is:[19][34]

) is the mean water-depth, slowly varying in space and time. Similarly, the mean horizontal momentum evolves as:[19][34]

induced by the wave motion – and also the

which is an exact result for periodic progressive water waves, also valid for nonlinear However, its validity strongly depends on the way how wave momentum and mass

phase velocity for

Eulerian flow velocity

with the mean mass transport equal to

E is valid within

wave channel, the second definition (S2) is more appropriate. These wave systems have zero mass flux and

In contrast, according to Stokes' first induced mass flux in the wave propagation direction, which

undertow.

So in general, there are quite some subtleties involved. Therefore also the term pseudo-

of the mean flow

defined as:[34]

y, the mean Eulerian velocity

depth, slowly varying in space and time. Similarly, the mean



with d the still-water depth (the sea bed is at the identity matrix and is the

Note that mean horizontal momentumstill-water depth d is a constant), in agreement with

The system of equations is closed through the description of the waves. Wave energy propagation is described through the waveand nonlinear wave interactions):

The wave kinematics are described through the wave

with the angular frequency ω a function of the (angular) dispersion relation. For this to be possible, the wave field must be curl of the wave-crest conservation, it can be seen that an initially field stays irrotational.

Stokes drift

Main article: Stokes drift

When following a single particle in pure wave motion wave theory, a first approximation gives closed elliptical orbits for water particles.However, for nonlinear waves, particles exhibit a expression can be derived from the results of Airy wave theory (see the second-order wave properties).after one wave cycle divided by the theory:[38]



water depth (the sea bed is at z=–d), is the wave radiationis the dyadic product:

momentum is only conserved if the sea bed is horizontal (is a constant), in agreement with Noether's theorem.

The system of equations is closed through the description of the waves. Wave energy propagation is described through the wave-action conservation equation (without dissipation and nonlinear wave interactions):[19][24]

The wave kinematics are described through the wave-crest conservation equation:

a function of the (angular) wavenumber k, related th. For this to be possible, the wave field must be coherent

crest conservation, it can be seen that an initially irrotational

When following a single particle in pure wave motion accordingwave theory, a first approximation gives closed elliptical orbits for water particles.However, for nonlinear waves, particles exhibit a Stokes drift for which a secondexpression can be derived from the results of Airy wave theory (see the table above on

).[37] The Stokes drift velocity , which is the particle drift after one wave cycle divided by the period, can be estimated using the results of linear

-stress tensor, is

is only conserved if the sea bed is horizontal (i.e. the

The system of equations is closed through the description of the waves. Wave energy action conservation equation (without dissipation

vation equation:[35]

, related through the coherent. By taking the irrotational wavenumber

according to linear Airy wave theory, a first approximation gives closed elliptical orbits for water particles.[36]

for which a second-order table above on

, which is the particle drift , can be estimated using the results of linear



so it varies as a function of elevation. The given formula is for Stokes first definition of wave celerity. When is integrated

is recovered.[38]

Standing on a beach and watching the waves roll in and break, one might guess that water is moving bodily towards the shore.of floating debris beyond the breakers, we can see it move towards the shore on the crest of a wave, and move the same distance backward with the trough of the wave.in a roughly circular path perpendicular to the water’s surwaves, a mixture of longitudinal and transverse waves.deformations of the sea surface.water molecules remain at the same positionthe shore. Most ocean waves are produced by wind, and the energy from the wind offshore is carried by the waves towards the shore.

We distinguish between deep-between deep and shallow water waves has nothing to do with absolute water depth.determined by the ratio of the water's depth to the wavelength of the wave.

The water molecules of a deepdecreases with the distance from the surface. The motion is felt down to a distance of approximately one wavelength, where the wave's energy becomes negligible.

The orbits of the molecules of shallow



nction of elevation. The given formula is for Stokes first definition of wave integrated over depth, the expression for the mean wave momentum

Standing on a beach and watching the waves roll in and break, one might guess that water is moving bodily towards the shore. But no water is piling up on the beach. of floating debris beyond the breakers, we can see it move towards the shore on the crest of a wave, and move the same distance backward with the trough of the wave. in a roughly circular path perpendicular to the water’s surface. Water waves are

, a mixture of longitudinal and transverse waves. Surface waves in oceanography are deformations of the sea surface. The deformations propagate with the wave speed, while the water molecules remain at the same positions on average. Energy, however, moves towards

Most ocean waves are produced by wind, and the energy from the wind offshore is carried by the waves towards the shore.

-water waves and shallow-water waves. The distinctbetween deep and shallow water waves has nothing to do with absolute water depth.determined by the ratio of the water's depth to the wavelength of the wave.

The water molecules of a deep-water wave move in a circular orbit. The diameter of thedecreases with the distance from the surface. The motion is felt down to a distance of approximately one wavelength, where the wave's energy becomes negligible.

The orbits of the molecules of shallow-water waves are more elliptical.

nction of elevation. The given formula is for Stokes first definition of wave over depth, the expression for the mean wave momentum

Standing on a beach and watching the waves roll in and break, one might guess that water is Watching a piece

of floating debris beyond the breakers, we can see it move towards the shore on the crest of a The debris moves

Water waves are surface Surface waves in oceanography are

The deformations propagate with the wave speed, while the Energy, however, moves towards

Most ocean waves are produced by wind, and the energy from the wind offshore is

The distinction between deep and shallow water waves has nothing to do with absolute water depth. It is determined by the ratio of the water's depth to the wavelength of the wave.

water wave move in a circular orbit. The diameter of the orbit decreases with the distance from the surface. The motion is felt down to a distance of approximately one wavelength, where the wave's energy becomes negligible.



The change from deep to shallow water waves occurs when the depth of the water, d, becomes less than one half of the wavelength of the wave, λ. When d is much greater than λ/2 we have a deep-water wave or a short wave. When d is much less than λ/2 we have a shallow-water wave or a long wave.

The speed of deep-water waves depends on the wavelength of the waves. We say that deep-water waves show dispersion. A wave with a longer wavelength travels at higher speed. In contrast, shallow-water waves show no dispersion. Their speed is independent of their wavelength. It depends, however, on the depth of the water. Shallow-water waves move at a speed that is equal to the square root of the product of the acceleration of gravity and

the water depth.

Deep-water waves in the ocean are wind-generated waves. They can be generated by the local winds (sea) or by distant winds (swell).

Ocean waves are produce by a variety of forces. Meteorological forces (wind, air pressure) produce seas and swells. Astronomical forces produce the tides. Earthquakes produce tsunamis. Tides and tsunamis are shallow-water waves, even in the deep ocean. The deep ocean is shallow with respect to a wave with a wavelength longer than twice the ocean's depth.

Tsunamis

A tsunami, also called seismic sea wave or tidal wave, is a catastrophic ocean wave, usually caused by a submarine earthquake occurring less than 50 km (30 miles) beneath the seafloor, with a magnitude greater than 6.5 on the Richter scale. Underwater or coastal landslides or volcanic eruptions also may cause a tsunami. The term tidal wave is more frequently used for such a wave, but it is a misnomer, for the wave has no connection with the tides. A tsunami can have a wavelength in excess of 100 km and period on the order of one hour. Because it has such a long wavelength, a tsunami is a shallow-water wave. Shallow-water waves move with a speed equal to the square root of the product of the acceleration of gravity and the water depth.

Problem:

In the Pacific Ocean the typical water depth is about 4000 m. What is the speed of a tsunami with a wavelength of 50 km.

• Solution:

50 km is much larger than 8000 m = 8 km. We have a shallow-water wave.

. gd = (9.8 m/s2)4000 m = 39200 (m/s)2. v = 198 m/s.

The tsunami travels at about 200 m/s, or over 700 km/hr.



The rate at which a wave loses its energy is inversely related to its wavelength. A tsunami not only propagates with a high speed, it also can travel a great, transoceanic distance with only limited energy loss.

Link:

• The physics of tsunamis

In the deep ocean, the amplitude of a tsunami is only a few feet. It cannot be felt aboard a ship or seen from the air in the open ocean. When the tsunami approaches the coastline, its speed decreases and its amplitude increases. (The power is proportional to the square of the amplitude times the speed. As the speed decreases, the amplitude increases.) The amplitude can grow to a height exceeding 100 feet. The tsunami can strike with devastating force.

Earthquakes generate tsunamis when the sea floor abruptly deforms and displaces the water above from its equilibrium position. Waves are formed as the displaced water under the influence of gravity attempts to regain its equilibrium. The initial size of a tsunami is determined by the amount of vertical sea floor deformation.

Tides

The earth and the moon orbit each other. They revolve about their common center of mass. Gravity provides the centripetal acceleration. The moon is constantly falling towards the earth and the earth is constantly falling towards the moon. But while each body moves on a curved trajectory, the distance between it and the other body stays constant.

The gravitational force between two objects is inverse proportional to the square of their distance. The distance between the earth and the moon is usually taken to be the distance between their centers. But the earth is an extended object. The gravitational acceleration due to the moon is larger than average on the side facing the moon, and smaller than average on the side facing away from the moon. Any loose material on the side of the earth facing the moon would accelerate at a higher than average rate towards the moon and move in a tighter orbit if not bound to the earth by gravity. Any loose material on the side of the earth facing away from the moon would accelerate at a lower than average rate towards the moon and move in a wider orbit if not bound to the earth by gravity. The waters of the oceans try to fall into these natural orbits, but the earth's gravity pulls them back. Water on the side of the earth facing the moon therefore forms a bulge outward from the center of the earth and toward the moon. Water on the side of the earth facing away from the moon forms a bulge outward from the center of the earth and away from the moon.

There are thus two separate tidal bulges in the earth's oceans, one on the side nearest the moon and one on the side farthest from the moon. The earth rotates once a day, so these bulges move across the earth's surface. There are two bulges, so each shore passes through two bulges a day. At those times, the tide is high. During the times when the seashore is between bulges, the tide is low. Because the moon moves as the earth turns, the time interval between high tides is about 12 hours and 26 minutes, not exactly 12 hours. Since local water must flow to form the bulges as the earth rotates, there are cases where the tides are delayed



as the water struggles to move through a channel. However, even in those cases, the high tides occur every 12 hours and 26 minutes.

Link:

• Lunar Tides

The sun's gravity also contributes to the tides, but its effects are smaller and serve mostly to vary the heights of high and low tide.

1

1CREATED BY CAPTAIN.THIYAGARAJU BALASUBRAMANIAM

Documents

COASTAL ZONE MANAGEMENT NOTES - SCET CIVILvetscetcivil.weebly.com/uploads/1/3/2/7/13271550/... · COSTAL ZONE MANAGEMENT NOTES BY CAPT.THIYAGU CREATED BY CAPT.THIYAGARAJU BALASUBRAMANIAM