BREAKWATERS BREAKWATERS

Breakwater is a structure that protects Breakwater is a structure that protects the area in its lee from wave attack. the area in its lee from wave attack.

A protective structure of stone or concrete; extends from shore into the water to prevent a beach from washing away.

INTRODUCTION

Reduce the intensity of wave action in inshore Reduce the intensity of wave action in inshore waters and thereby reduce coastal erosion.waters and thereby reduce coastal erosion.

Maintain sufficient environmental flow and water Maintain sufficient environmental flow and water exchange behind the breakwater to ensure the exchange behind the breakwater to ensure the survival of existing sea grass and transplanted corals survival of existing sea grass and transplanted corals and algae.and algae.

PURPOSE OF BREAKWATER

TYPES OF BREAKWATERTYPES OF BREAKWATER

Rubble Mound BreakwaterRubble Mound BreakwaterCaisson BreakwaterCaisson BreakwaterPorous BreakwaterPorous BreakwaterFloating BreakwaterFloating BreakwaterSubmerged active BreakwaterSubmerged active BreakwaterFlexible BreakwaterFlexible BreakwaterVertical Wall BreakwaterVertical Wall Breakwater

RUBBLE MOUND RUBBLE MOUND BREAKWATERBREAKWATER

Cross-section of a typical rubble mound breakwater

The function of a rubble mound breakwater is to protect a coastal area from excessive waveaction.

The project consists of a 470-foot-long rubble The project consists of a 470-foot-long rubble mound breakwater extension, a 12-foot-deep mound breakwater extension, a 12-foot-deep entrance channel, and an 8-foot-deep main entrance channel, and an 8-foot-deep main access channel and maneuvering area.access channel and maneuvering area.

ADVANTAGESADVANTAGES DISADVANTAGESDISADVANTAGES

•Suitable For Irregular Bottom

•Suitable For Weak Soil.

•Simpler Construction

•Simpler Maintenance

• Required material increases rapidly with increased water depth.

CAISSON CAISSON BREAKWATERBREAKWATER

Caisson breakwaters typically have vertical sides and Caisson breakwaters typically have vertical sides and are usually used where it is desirable to berth one or are usually used where it is desirable to berth one or more vessels on the inner face of the breakwater.more vessels on the inner face of the breakwater.

They are relatively expensive to construct in shallow water, but in deeper sites they can offer a significant saving over revetment breakwaters.

Wave Interaction With Caisson BreakwaterWave Interaction With Caisson Breakwater

POROUS POROUS BREAKWATERBREAKWATER

Porous Breakwaters normally experience reduced Porous Breakwaters normally experience reduced Hydrodynamic Pressures.Hydrodynamic Pressures.

Also reduce the reflection of waves that are incident Also reduce the reflection of waves that are incident on the breakwater due to the dissipation of wave on the breakwater due to the dissipation of wave energy through the porous structure.energy through the porous structure.

Wave Passing a Porous Breakwater Wave Passing a Porous Breakwater

FLOATING FLOATING BREAKWATERBREAKWATER

A A floating breakwaterfloating breakwater is  is destined for the protection destined for the protection of marinas, in different of marinas, in different situations: wave protection, situations: wave protection, erosion protection and even erosion protection and even wakes formed from passing wakes formed from passing boat traffic.boat traffic.

ADVANTAGES OF FLOATING ADVANTAGES OF FLOATING BREAKWATERBREAKWATER

A Floating breakwater can prevent sea water pollution.A Floating breakwater can prevent sea water pollution.

The placement location of the floating breakwater can be easily The placement location of the floating breakwater can be easily changed.changed.

The construction period in the field is much shorter compared to the The construction period in the field is much shorter compared to the

fixed type breakwaterfixed type breakwater..

A submerged breakwater consist of a large buoyant A submerged breakwater consist of a large buoyant cylinder which is held horizontal beneath the free cylinder which is held horizontal beneath the free surface of water.surface of water.

SUBMERGED BREAKWATER

REEF BALL AS SUBMERGED BREAKWATER

Reef Balls can be used as submerged breakwaters to protect a beach from erosion or even to build up a beach that has already eroded.

  the evolution of pressure and turbulent the evolution of pressure and turbulent energy along a two-dimensional section of energy along a two-dimensional section of

the 3D domain is representedthe 3D domain is represented..

BREAKWATER BREAKWATER CONSTRUCTIONCONSTRUCTION

2005 Raccoon Island Breakwater 2005 Raccoon Island Breakwater Construction Phase II Construction Phase II

Location: Raccoon Island, 15 miles Location: Raccoon Island, 15 miles

SW of Cocodrie, LASW of Cocodrie, LADescription: Placed 60,000 tons of stone constructing 8 breakwaters and 1 continuous breakwater designed to allow sediment to build up behind them to rebuild a bird sanctuary island

Breakwater for Marine Fisheries Facilities in Breakwater for Marine Fisheries Facilities in Kuantan Port, Pahang.Kuantan Port, Pahang.

(completed 1991)(completed 1991)

FIG: 1 FIG: 2

Breakwater Construction in Marang, Terenganu. (in progress)

FIG :1 FIG : 2

ARMOUR UNITS

RUBBLE MOUND STRUCTURES and RUBBLE MOUND STRUCTURES and ARMOUR UNITSARMOUR UNITS

o The function of a rubble mound breakwater is to protect coastal area from excessive wave action.

• Rubble mound structures consisting of interior graded layer of stone and an outer armor layer of stone or specially shaped concrete units are employed in the coastal area as breakwater, jetties, groins, and shoreline revetments.

• An advantage of rubble mound structures is that failure of the armor cover layer is not typically sudden, complete.

• In some cases, it may be economical to use smaller size armor units, anticipate a certain amount of damage during a design storm, and provide for subsequent repair of the structure.

• Armor units must be of sufficient size to resist wave attack.

• However, if an entire structure were to consist of units of this size, the structure would allow high levels of wave energy transmission and finer material in the foundation or embankment below the structure could easily be removed.

• Thus the structure unit sizes are graded in layers, from the large exterior armor units to small quarry-run sizes and finer stone at the core and at the interface with the native soil bed.

• There are many variations in the cross section design of breakwaters depending on the design wave climate, breakwater orientation, water depth, stone availability, foundation conditions, and degree of protection required of the structure.

• A concrete cap is most commonly used with concrete armor units.

• Two layers of armor units are commonly used.

WHY ARMOR UNITSWHY ARMOR UNITS

Many different shaped concrete armor units are currently being used to protect the rubble mound breakwaters and other coastal structures.

These units usually have a higher stability coefficient than quarry stone.

Greater stability permits the use of lighter weight units and steeper structure side slopes, provided that the units do not move significantly and are structurally sound.

The cost of concrete armor unit forms can amount to significant percentage of the unit’s total manufacturing cost. This is especially true for the more complicated shapes such as the DOLOS.

ARMOR UNIT STABILITYARMOR UNIT STABILITY

• A key element in the design of any rubble mound structure is to determine the required armor unit size.

• This in turn dictates much of the remaining geometry of the structure (i.e., layer dimensions, sub layer unit sizes, structure slopes, crest width of the structure).

• The factors affecting the armor unit size, usually specified as the weight of the unit, are listed below.

Design wave characteristicsDesign wave characteristics• The design wave height at the structure is of critical importance.

• Some designers use the significant height although more conservative heights such as H10 have been used.

• The importance of the structure, how well the design wave height is known, and the desired safety factor will affect choice.

• The expected duration of attack by high waves during a design storm is also an important factor.

• If the water depth at the seaward side of the structure is sufficiently shallow the design wave will break before it reaches the structure.

• This will limit the wave height attacking the structure and will affect type of attack that occurs.

Armor unit characteristicsArmor unit characteristics

• The shape, specific gravity, and range of unit sizes in the armor layer are important.

• More angular rock will be more stable than rock that is rounded.

• Artificial concrete armor units are designed to have irregular interlocking shapes while maintaining sufficient layer porosity when in place.

• Narrower stone size ranges are preferred for armor layers as very fine sizes are easily removed from the structure and finer sizes decrease the layer porosity which decreases its ability to relieve under layer pressure exerted by wave action.

• Lower layer porosities will also increase the elevation of the wave run up on the structure.

• However, specifying too narrow of the size range to a quarry operator increases the effort and thus cost of obtaining the rock.

Armor layer slopeArmor layer slope

• The flatter the slope the smaller the size of the armor unit required for stability to wave attack.

• Smaller sizes yield thinner armor layers but flatter slopes require longer layers.

Trunk versus headTrunk versus head

• The head or end of a structure is typically exposed to more concentrated wave attack than the trunk or side of the structure.

• For more complex structures it is common to

have flatter slopes and/or larger armor unit sizes at the head to protect against the greater wave attack.

OvertoppingOvertopping

• The structure may be designed for moderate or significant wave overtopping depending on the structure purpose and design criteria.

• For significant overtopping there is less return flow on the seaward face of the structure but greater action on the leeward face.

• This might allow smaller seaward armor unit sizes and steeper slopes but more attention will have to be placed on the design of the structure crest and lee side.

Placement methodPlacement method

• Depending on the construction procedure and care taken as well as the complexity of the structure, the armor unit placement may vary from plain dumping of the units to selective placement of individual units.

• Selective placement of the units will produce a more stable armor layer.

Layer dimensionsLayer dimensions

• Thicker armor unit layers offer more reserve stability if the armor layer is damaged during a storm.

• It is imperative that damage during a storm not proceed to the point where under layers are exposed to wave attack.

Allowable damageAllowable damage

• It is difficult to predict the amount of damage that will occur to a given armor unit layer for a given design storm.

• But some information that is available would allow selection of a smaller armor unit with the related economic benefits in anticipation of repairing the structure after the damage has occurred.

• Smaller units are easier to obtain from a quarry and easier to transport as well as requiring less total volume, so their cost is less.

Determination of Armor Unit StabilityDetermination of Armor Unit Stability• The hydrodynamic and armor unit interaction forces are very complex so

a completely analytical development of an equation for armor unit stability in not practicable.

• Heavy recourse must be made to experiments.

• The basic problem is to determine the required weight W of an armor unit having a particular shape and specific gravity S (in air), when exposed to waves of a given height and when placed on a structure face having a given slope u.

• From a rough analysis of the forces involved one can define a stability number for an armor unit

• Ns = H/(S - 1)(W/gs)1/3 (1)

• where gs is the specific weight of the stone or concrete armor unit.

• The stability number can be thought of as a dimensionless wave height and the term in the denominator that is raised to the one-third power is an effective diameter of the unit.

• A number of wave tank experiments have been run (Hudson, 1959) to relate Ns to the face slope and the armor unit shape at incipient failure of the armor units on the face.

• Basically, the experiments involved building an armor unit slope and exposing it to increasing wave heights until failure was observed.

• This failure point defined the stability number.

• The result is Ns = (KD cotu)1/3 (2)

• where KD is a dimensionless coefficient that depends on the armor unit shape, method of placement, location on the structure head or trunk, and whether the incident wave breaks before reaching the structure or on the structure face slope.

• Combining Eqs. (1) and (2) yields the classic Hudson equation for armor unit stability.

• W = gsH3 / KD(S - 1)3cotu

STABILITY FORMULAESTABILITY FORMULAE

• Many different equation with various parameter.

• Different criteria used to judge stability.

• Best to check with Hudson equation.

• Larger Kd is dangerous because of non interlocked condition, which is nearly impossible to avoid.

• Also, armor layers are easily damaged during construction and nearly impossible to repair to original condition.

CONCRETE ARMOR UNIT SHAPESCONCRETE ARMOR UNIT SHAPES

• Thousands of shapes

• Many different applications

• Most shapes have been patents of 1950’s and 1960’s.

TYPES OF ARMOR UNITSTYPES OF ARMOR UNITS• ACCROPOD

• AKMON• ANTIFER BLOCK• BEEHIVE• COB• CUBE• DOLOS• GAMMA-L• GASSHO• GROBBELAAR• HEXALEG• HOLLOW SQUARE

• HOLLOW TETRAHEDRON• SANREN• SEALOCK• STOLK CUBE• SVEE• TETRAPOD• TOSKANE• TRIBAR• X-BLOCK

CLASSIFICATION OF ARMOR UNITCLASSIFICATION OF ARMOR UNIT

TETRAPODTETRAPOD

• A Tetra pod is a four-legged concrete structure used as armor unit on breakwaters.

• Tetra pods were designed to remain stable under even the most extreme weather and marine conditions, and when arranged together in lines or heaps, they create an interlocking, porous barrier that dissipates the power of waves and currents.

• The unit was originally developed in 1950 by Laboratories' Dauphinois d'Hydraulique in Grenoble, France

TETRAPODTETRAPOD

TETRAPODTETRAPOD

• The Tetrapod's shape is designed to dissipate the force of incoming waves by allowing water to flow around rather than against it, and to reduce displacement by allowing a random distribution of Tetra pods to mutually interlock.

• Tetrapod, in Greek means "four legged." If you observe a tetrapod you will see four legs protruding from a middle structure just like a star fish. These four-legged tetrapods are nothing but concrete made structures used to prevent coastal erosion. The name has become so famous that now even the three-legged concrete structures are also known as tetrapods.

TETRAPODTETRAPOD

• How do they work?• The tetrapods are designed in such a way that they dissipate the

force of incoming waves by making the water flow around rather than against them. They also reduce displacement by allowing the random distribution of tetrapods to mutually interlock. Due to their weight and design, tetrapods can remain stable even under the most extreme weather conditions. A number of tetrapods arranged together form an interlocking, porous barrier that dissipates the power of waves and currents.

• Prolonged effects on Tetrapods• No structural design or concrete structures used in breakwaters can

last forever. Even tetrapods or any other form of concrete blocks, tend to become dislodged over a period of time due to the forces of nature constantly crashing against them. Thus all the concrete structures are replaced after some point of time. Tetrapods are generally monitored through satellite photography for any kind of displacement or change in structural form.

Criticism of TetrapodsCriticism of Tetrapods

• Though tetrapods are helpful structures, they have also faced a lot of criticism mainly because of their shape. Many people argue that they pose a danger to swimmers, surfers, and boaters, while others say that tetrapods in fact accelerate beach erosion by disturbing the natural processes that shape the coastal environment. Tetrapods have also been criticized for spoiling the natural coastal scenery. It is also been said that the wave action on tetrapods pulls the sand away from the shore faster than what happens in the natural process.

• Thus, even though tetrapods are widely criticized, the fact remains that they cannot be neglected. The main feature of a tetrapod lies in its design, which is not found in nature. Tetrapods are a symbol of artificiality and not aesthetics, and in spite of all the criticism have been extremely helpful in numerous ways.

DOLOSDOLOS

• A dolos (plural dolosse) is an unusually-shaped concrete block weighing up to 20 tons which is used in great numbers to protect harbor walls from the force of the sea. They were developed in East London, a port city in South Africa, in 1963 and are found in their millions around the world.

• Construction• Dolosse are normally made from un-reinforced concrete,

poured into a steel mould. The concrete will sometimes be mixed with small steel fibers, to strengthen it in the absence of reinforcing. Construction is done as close as possible to the area of application as a result of their great weight.

DOLOSDOLOS

Origin of shape

What induced either man to choose such a shape is not known, though there is a legend that it was inspired by the difficulty the East London harbor authorities had pulling apart a large pile of similarly-shaped anchors for salvage.

DOLOS USEDOLOS USE

• They are used to protect harbor walls, breakwaters, and shore earthworks. They are also used to bind sea-sand to prevent erosion. In the order of 10 000 dolosse are required for a kilometer of coastline.

• They work by dissipating, rather than blocking, the energy of waves.

Their design presents very little surface area to the wave action, making them difficult to dislodge, unlike rectangular blocks that can be swept away by heavy seas. Though they are placed into position on top of each other by cranes, over time, they tend to get further entangled as the waves shift them about. Their design ensures that they form an interlocking, but porous, wall.

• They are often numbered on the outside so that satellites can

periodically track their movement. This helps engineers gauge whether they need to add more dolosse to the pile.

Armor Unit ComparisonsArmor Unit Comparisons

• Economic Advantage• Published research has shown that the Core-loc offers

improved stability over other armor units, permitting a single layer of armor with higher stability and lower cost in many applications.

• The following table indicates the costs of various armor units relative to Core-loc including an allowance for the royalties: 

• Table 1: Costs of different armor unit types relative to Core-loc.

• In addition to the savings produced by using the Core-loc, the project benefits from the technical back-up and quality control input of the licensee CLA and the licensor CHL.

Core-loc Accropod Dolos Tetrapod Cube

100% 123% 160% 235% 247%

Design PhilosophyDesign Philosophy

• The design philosophy of the Core-loc is based on the use of a single layer of units. Slender interlocking units with high voids ratio such as dolosse can be lighter than the equivalent stable concrete cubes. Such slender units need to be placed in a double layer to allow for movement and breakage. Cubes on the other hand are robust but need to be more massive because of their lower stability characteristics. The Core-loc is intended to benefit from both good interlocking characteristics and the intrinsic strength of a more bulky unit.

Design PhilosophyDesign Philosophy

• A "single layer" armor system is sometimes incorrectly interpreted as less reliable than "double layer" systems. To compare the reliability with which units can be applied, the same volume of concrete should be considered. If a "double layer" approach is to use the same volume of concrete as that of a single layer, it implies that its unit size needs to be decreased to achieve the required coverage, increasing the number of units to be placed. A reduced unit size implies a reduced design wave height that the structure could withstand. To illustrate the significance of this concept the following Table 2 shows the equivalent sizes and total number of units that would have been required for the Port St Francis (South Africa) breakwater:

• Table 2: Comparison of armor units for equal total volumes of concrete. Case Port St Francis.

Unit Mass (t) Number of Units

Total Concrete Mass (t)

Design Wave height (m)

3-D Image

Core-loc 15.0 800 12000 7.1

Accropod 11.8 1017 12000 6.0

Dolos 6.3 1905 12000 5.1

Tetrapod 3.2 3750 12000 4.1

Cube 2.2 5454 12000 2.6

• Table 2 shows that Core-locs are relatively larger and more stable than other units for the same volume of concrete.

• Alternatively if all units were designed to survive a similar wave height, the relative unit size (Accropod, Dolos, Tetrapods, Cube) would be greater than the Core-loc size as illustrated in the economic comparison in Tables 1 and 3.

• It must be borne in mind that many other factors will apply in the final design of a specific breakwater such as plant capability, access, materials availability, typical sea conditions that affect visibility and ease of construction, breakwater crest and slope design.

• Table 3: Comparison of armor units for equivalent design wave height. Case Port St Francis.

Table 3: Comparison of armor units Table 3: Comparison of armor units for equivalent design wave height. for equivalent design wave height.

Case Port St Francis.Case Port St Francis.Unit Mass (t) Total

Concrete Mass (t)

Total concrete mass (%)

Design Wave height (m)

Core-loc 15.0 12000 100% 8.7

Accropod 17.4 13700 114% 8.7

Dolos 15.0 17800 148% 8.7

Tetrapod 21.7 25200 210% 8.7

Cube 21.7 28400 236% 8.7

Table 3 shows the cost saving that can be expected when using Core-loc. The choice of stability coefficients, armor slope angles and risk of failure criteria can influence these figures, but the cost savings shown here reflect values typically used for design purposes.

CUBIPOD vs CUBECUBIPOD vs CUBE

Easy fabrication and placement

High structural strength

Low risk to progressive failure

Low hydraulic stability

CUBIPOD vs CUBECUBIPOD vs CUBE

• Cube advantages

• Decrease OVERTOPPING

• High hydraulic stability: KD≈ 5*Kdcube

• pods: separation of armor unit faces

• pods: increase friction with filter layer

ARMOR SELECTION ARMOR SELECTION CRITERIACRITERIA

• Consider purpose of armor

• Hydraulic stability

• Structural capacity, material

• Engineering performance vs cost

Volumetric efficiency

Ease of construction

CONCLUSIONCONCLUSION

• Concrete armor is typically economical when there is no stone or the stone size is large.

• Concrete armor design requires higher design reliability, but concrete armor units are usually stable for a wider range of wave heights.

• Silt curtains

Silt curtainsSilt curtains

• A floating “geotextile” material placed so as to minimize sediment transport from a disturbed area adjacent to or within a body of water.

• A “geotextile” material is defined as a synthetic fabric used to retain soil while allowing water to pass through.

• Silt curtains are also known as silt fences, turbidity curtains etc.

PurposePurpose

• To provide sedimentation protection for a water course from up slope land disturbance

• To provide sedimentation protection during dredging and filling within water course.

• Recent use is in controlling oil spillage.

How does it work?How does it work?

• A silt curtain is designed to deflect and contain sediment within a limited area and provide enough residence time so that soil particles will fall out of suspension and not travel to other areas.

Silt curtain effectivenessSilt curtain effectiveness

• Silt curtain effectiveness is defined as the degree of turbidity reduction outside the curtain relative to turbidity levels inside curtain enclosure.

• Factors that determine curtain effectiveness are :

• Quantity and type of materials in suspension

• Area and configuration of curtain enclosure

• Method of mooring• Hydrodynamic conditions• Condition of silt curtain• Nature of operation.

Structural design criteriaStructural design criteria

• Current velocity• Wind velocity• Tidal action• Water depth• Wave height• Bottom conditions (for

anchoring)• Service life

Components of a single sectionComponents of a single section

• Flotation material (float)

• Tension member/cable

• Curtain fabric• Metal fittings• Bottom weight• Anchoring wire• Anchor

standard specifications standard specifications

• GENERAL CONSTRUCTION

• Unit length:3m• Float is columnar shaped and covered by orange colored

PVC tarpaulin.• Vertical curtain joint between each unit is done by rope.• Tension belt is sewn and placed under float on both

sides of fabric.• Tension Belt has anchoring point of galvanized steel

metal fittings at both ends .• Anchor block is placed on both sides of unit.

Standard specificationsStandard specifications

• Properties of each component

• PVC tarpaulin float cover• Tensile strength in warp direction :50Kn/m• Tensile strength in weft direction :50Kn/m

• Foamed polystyrene float• Diameter 60cm• Buoyancy 2450N/m• Compression strength 60Kpa(at 5% strain)

Standard specificationStandard specification

• Polyester woven curtain fabric• Tensile Strength in warp direction: 260kN/m • Tensile Strength in weft direction: 260kN/m • Maximum Elongation in both directions: 20%

• Polyester tension belt• Tensile strength : 115Kn X 2 (both sides)• Maximum elongation : 20%

• Bottom chain ballast• Weight : 10Kgf/m

Construction specificationConstruction specification

• Barriers should be of bright color (yellow or orange) so that it is clearly visible.

• Seams in fabric should be either vulcanized , welded or sewn and should develop full strength of fabric.

• Flotation devices shall be flexible, buoyant units, contained in an individual flotation sleeve or collar attached to the curtain .

• Freeboard of at least 3 inches above water surface to be maintained.

Materials usedMaterials used

• FABRICS• Reinforced PVC coated• Reinforced alloy coated• Reinforced urethane coated• Woven polyolifin mesh

• TENSION MEMBER• Coated galvanized cable

• FLOTATION• Styrofoam • Rolled polyolifin foam

Fabric surface should be:Fabric surface should be:

• Easy cleaning.

• Resistant to marine growth.

• Resistant to ultra violet rays.

• Resistant to mildew.

Types of silt curtainTypes of silt curtain

• STILLWATER • Used in protected areas where there is no current and

area is sheltered from wind and waves.

• FASTWATER• Used in areas where wind/waves can affect the curtain

or there is small current running ( ~ 2 knots).

• RUFFWATER• Used in areas where considerable current may be

present (~ 3 knots) ,where tidal action may be present , where curtain is potentially subject to wind and wave action.

InstallationInstallation

• Loading on barge.

• Joint connection between each unit.

• Dropping anchor block.

• Sending each unit into the sea.

• Connect anchor ropes to the unit.

Joint connections between unitsJoint connections between units

Dropping of anchor blocksDropping of anchor blocks

Sending units into seaSending units into sea

• The individual sections are about 10ft long.

• Another way of installation is to first join the sections at harbor and then tow them to the site by boats at speeds of 2 to 3 knots.

• Curtains about 2000ft long have been towed this way.

• Curtain should always remain furled until it has been deployed at operation site.

Installed curtain at siteInstalled curtain at site

Mooring/AnchoringMooring/Anchoring

• Curtains should be anchored from section joints (preferably every 50ft or 100ft) in a radial pattern.

• Anchoring to be done on both sides in case the curtain is exposed to reversing tidal currents.

• Self buoying anchors should be used. The minimum buoy weight to be in accordance with established norms followed for different bottom conditions.

• With increased velocities anchor weights have to be increased.

Configurations Configurations

• Maze configuration :used in waterways (specially in rivers) with boat traffic.

• U configuration : used in places with no exposure to reversing currents.

• elliptical / circular configuration : used in regions prone to tidal actions or reversing currents.

• Curtain length 500’~1500’ for U config.• Curtain length 1000’~3000’ for circular config.

configurationsconfigurations

Duration of deploymentDuration of deployment

• FACTORS AFFECTING DURATION OF DEPLOYMENT ARE:

• Rate of accumulation of fluid mud.• Discharge rate of material.• Initial bottom gap • Area of enclosure.

MaintenanceMaintenance

• Move curtain away from turbidity source just before fluid mud layer reaches the lower edge of skirt.

• Replace worn or broken anchor lines.• Repair tears in curtain fabric.• Tears in flotation pocket can be repaired in

water with a hand type pop rivet gun.• Moderate tears on skirt can be repaired on land

with a vinyl repair kit or a special heat gun.• Properly maintained and stored curtain can be

reused.

Removal of curtainRemoval of curtain

• Skirt to be protected against damage while being dragged out of water.

• In case of a long skirt the crew can install furling lines before pulling it out.

• The site selected to tow the curtain ashore should be free of sharp rocks, broken cement debris etc. to minimize damage while hauling curtain over the area.

Hauling of curtains Hauling of curtains

Cleaning of curtainCleaning of curtain

• Marine growth is cleaned immediately upon removal from water.

• The curtain is rinsed.

• It is then dried.

• Furled and stowed safely.

• Stowing is done in such a way that it is not exposed to direct sunlight.

StowageStowage

DESIGN OF DESIGN OF

BREAKWATERSBREAKWATERSA CASE STUDYA CASE STUDY

BreakwatersBreakwaters

• What are breakwaters?

• Why do we need them?

Types of breakwatersTypes of breakwaters

• Complete

• Partial

• Porous

Desirable FactorsDesirable Factors

• Light weight

• Cost effectiveness

• Environment friendliness

• Reusability

Design ProcessDesign Process

• Functionality

• Technology

• Environment

• Cost and Benefit

• Construction

Design ConsiderationsDesign Considerations

• Water Depth

• Wave Force Estimation

• Soil Mechanics

• Area to be protected

Wave ForcesWave Forces

• Climatic conditions of the region

• Dynamic

• Use of Wave Spectra

Soil MechanicsSoil Mechanics

• Type of Soil

• Soil Bearing Capacity

• Bottom topography

Wave Force Estimation on A Wave Force Estimation on A Vertical WallVertical Wall

• Non-breaking Waves

• Breaking (plunging) waves with almost vertical fronts

• Breaking (plunging) waves with large air pockets

Non-breaking Waves

Breaking (plunging) waves with almost vertical fronts

Breaking (plunging) waves with large air pockets

Wave Crest At FrontWave Crest At Front

Wave Trough At FrontWave Trough At Front

Design ProcedureDesign Procedure

• Design Conditions: depth, waves

• Selecting dimensions

• Wave loading

• Soil mechanics

• Stability

• Stress analysis

• Structural detailing

A Case StudyA Case Study

• Construction of a small craft-harbor at Sandspit, in the Queen Charlotte islands of British Columbia(1988).

• Severe Climatic Conditions

ProjectProject

• National Park on Moresby Island, in the Queen Charlotte

• Preservation, Local Economy.

• Recreational site

• A small craft harbour for fishing industry and terminus for small cruise (1989-1995)

NeedsNeeds

• Basin and entrance channel by dredging 250,000 cubic metres of beach gravels.

• 450 metre long rubble-mound breakwater constructed from approximately 100,000 tonnes of quarried rock.

Design needs of breakwaterDesign needs of breakwater

• Severe climatic conditions

• Remote location and importance

• 50 years of service life desired

• Performance of rock used

Climatic ConditionsClimatic Conditions

StudyStudy

• Hourly wind speed and direction from January 1, 1965 to December 31, 1993.

• Wind and wave scatter plots and threshold storms over 50 knots wind speed.

• Effects of refraction, shoaling, diffraction, and breaking over the complex bathymetry.

Breakwater designBreakwater design

• Tidal range of 8.0 m• Class B facility.• This allows a maximum wave height in

the harbour entrance of 1.0 m, and a maximum wave height within the harbour of between 0.25 m and 0.5 m, depending upon the size of vessels being moored.

• Economic structure.

Cross-Sectional DesignCross-Sectional Design

Structural DesignStructural Design

• Double layer of armour stone on the offshore face.

• Single layer of select armour stone on the leeside.

• Overtopping Analysis

• Offshore Slope 1:2

• Leeside Slope 1:1.5

StructureStructure

• It was intended that the armour stone be extremely durable.

• Gradations of armour stone

• The longest dimension was required to be not greater than 2.5 times the least dimension.

ConstructionConstruction

• A suitable rock supply as close to the site as possible.

• ‘Diorite’ used, available adjacent to site.

• Later different rock used which was defective.

• Overlay constructed.

ConclusionConclusion

• Technical limits tested.

• Importance of material selection

• Contracting

• Inspection

• Balance between objectives and cost effectiveness

• Since spring 1997, has performed well

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