Environmental Science -1_1

8/4/2019 Environmental Science -1_1

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Environmental ScienceEnvironmental Science


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Contributing Faculty

M.M. Ghangrekar, Ph.D.Associate ProfessorDepartment of Civil Engineering(Section-2 Coordinator)

A K Gupta, Ph.D.Associate Professor,

Civil Engineering

M K Dash, Ph.D.Assistant Professor,

Oceans, Rivers, Atmosphere and Land Sciences


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Tentative time

Section-II

Participating Facul

1 M M G


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Thickness of Different structure of Earth

Crust 5km 70km

Mantle 2900km

Outer core 2300kmInner core 1200km


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Crust:

The outermost layer of the Earth is the crust.

This comprises the continents and ocean basins.

The crust has a variable thickness, being 35-70 km thick in the continents

and 5-10 km thick in the ocean basins.

The crust is composed mainly ofalumino silicates.

Mantle:

The next layer to the crust is the mantle, which is composed mainly of

ferro-magnesium silicates.

Its thickness is about about 2900 km and is separated into the upper and

lower mantle.

This is where most of the internal heat of the Earth is located. Large

convective cells in the mantle circulate heat and may drive plate tectonicprocesses.


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Core:

The last layer is the core, which is separated into the liquid outer core

and the solid inner core.

The outer core is 2300 km thick and the inner core is 1200 km thick.

The outer core is composed mainly of a nickel-iron alloy, while the

inner core is almost entirely composed of iron.

Earth's magnetic field is believed to be controlled by the liquid outer

core.

The Earth is separated into layers based on mechanical properties in addition

to composition. The topmost layer is the lithosphere, which is comprised of thecrust and solid portion of the upper mantle. The lithosphere is divided into

many plates that move in relation to each other due to tectonic forces.

The lithosphere essentially floats atop a semi-liquid layer known as the

asthenosphere. This layer allows the solid lithosphere to move around since

the asthenosphere is much weaker than the lithosphere.


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Lithosphere

(The topmost layer is the lithosphere, which is comprised of the crust and solidportion of the upper mantle)

Reservoir

( Reservoir contains voids,

allowing Flow of liquid into its

main body )

Non-Reservoir

Permeable

(The reservoir which yields water

easily, economically)

Impermeable

(Ex. Clay)

Porous Fractured Karstic

(Basing on water bearing property)

(Basing on water yield)

(Depending on the geological evolution of void space)


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Porous Medium

Such a medium includes countless irregular voids of random sizes and

shapes comprising pore spaces, which are also referred to as the interstices

between the individual solid particles of sand or pebbles

Each pore is connected with adjacent ones by constricted channels of

different sizes

collectively, pores and channels may form a completely interconnected

network of voids through which water can move in various directions

such a set up in rock mass will be referred to as the porous medium

Smaller grain sizes of solid particles the more the regular the flow path

In a coarse-grained medium the water will meet less resistance from thefrom the solids but the flow path is more irregular and the flow rate has greater

amplitudes of fluctuations


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Porous Reservoir

Fluvial Sand Dunes Glacial Sedimentary

Alluvial Deposit

Eskers Kames

Clastic Non-Clastic

Alluvial Fans

Alluvial FillsDelta

Coastal


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Alluvial Fans

An alluvial fan is a fan-shaped

deposit formed where a fast

flowing stream flattens, slows,

and spreads typically at the exit

of a caynon onto a flatter plain.

A convergence of neighbouring

alluvial fans into a single apron

of deposits against a slope is

called a bajada, or compoundalluvial fan.


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Formation of Alluvial Fans:

These formations are fluvial origin

and occur where a stream leaves a

steep valley and slows down as itenters a plain

Owing to the slowing of flow,

coarse-grained solid material

carried by the water is dropped. As

this reduces the capacity of the

channel, the channel will change

direction over time, gradually

building up a slightly mounded or

shallow conical fan shape.


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This fan shape can also be

explained with a thermodynamic

justification:

the system of sediment

introduced at the apex of the fan

will tend to a state which

minimizes the sum of the

transport energy involved inmoving the sediment and the

gravitational potential of material

in the cone.

There will be iso-transport energy lines forming concentric arcs about the

discharge point at the apex of the fan. Thus the material will tend to be deposited

equally about these lines, forming the characteristic cone shape.


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Alluvial Fan are very noticeable and abound especially in arid and

semiarid regions

The growth of alluvial Fan was initiated when the climate was more humid

and rain fall was abundant

The extent of Alluvial Fan depends on the drainage basin , slope, size,

climate and characteristics of rocks in the source area

the fine grained debris is deposited further downstream and may be

cross bedded, massive or thick bedded

Groundwater flow in alluvial fans is replenished by percolation of river

water

Most often the water appear in the form of springs, otherwise it may

continue its journey further downstream where it emerges as surface flow

Alluvial fans provide groundwater in coastal deserts areas. In arid regions

they are the potential source of aquifers.


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Alluvial Fills

Alluvial Fill are the result of an existing

valley being filled with alluvium.

The valley may fill with alluvium for many

different reasons including: an influx in

bed load due to glaciation or change in

carrying capacity which causes the

valley, that was down cut by the stream,

to be filled in with material (Easterbrook).

The stream will continue to deposit

material until an equilibrium is reached

and the stream can transport the material

rather than deposit it.

This equilibrium may last for a very short

period, such as, after glaciation, or for a

very long time if the conditions do not

change.


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The fill terrace is created when the

conditions change again and the streamstarts to incise into the material that it

deposited in the valley.

Once this occurs benches composed

completely of alluvium form on the sides

of the valley.

The upper most benches are the fill

terraces. As the stream continues to cut

down through the alluvium the fill

terraces are left above the river channel

(sometimes 100 m or more).

The fill terrace is only the very highest

terrace resulting from the depositional

episode, if there are multiple terraces

below the fill terrace these are called cut-

in-terraces.


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These are formed as a result of weathering and the water in fills or where

the relief is favorable and the rainfall sufficient to provide the driving force for

movement

Gravels which are coarsest product of erosion are moved shorter

distance from their source and are deposited in more restricted areas than sand

clay and mod

Fluvial gravels are wide spread, especially in arid regions, where they fill

the valleys of rivers, surface depressions or fault zones

Alluvial fills in arid regions are known as Wadis

The groundwater is found in the voids of Gravels. They make up potential

groundwater reservoir for local use

In arid regions these are the primary locations for water-well excavation

to supply the nearby villages


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A delta is a landform where the mouth of a

river flows into an ocean, sea, estuary, lake

or another river.

A delta is formed only when a channel

deposits sediment into another body of

water.

It builds up sediment outwards into the flatarea which the river's flow encounters (as a

deltaic deposit) transported by the water

and set down as the currents slow.

Deltaic deposits of larger, heavily-laden

rivers are characterized by the main

channel dividing amongst often substantial

land masses into multiple streams known

as distributaries.Nile river Delta

Delta Deposits


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Nile river Delta

These divide and come together again

to form a maze of active and inactive

channels.

The deposit at the mouth of a river is

usually triangular in shape and size.

The triangular shape and the increased

width at the base are due to blocking ofthe river mouth, with resulting

continual formation of distributaries at

angles to the original course.

A delta can sometimes be

misinterpreted as an alluvial fan.

The two terms, however, are not

interchangeable.

A delta is formed in water and an

alluvial fan occurs on land.
http://en.wikipedia.org/wiki/Alluvial_fanhttp://en.wikipedia.org/wiki/Alluvial_fan


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Delta is a subarea and submerged contiguous sediment mass

deposited in a body of water (Ocean or Lake) primarily by action of river

they are terrestrial depositions, not marine. However marine sedimentsmay be incorporated in delta fronts intercalating with alluvial deposits if

phases of subsidence alternate with phases of delta make up

Deltas are at the downstream ends of the basin, both the gradient and

the flow velocity decreases and suspended sediments and the bed loads

consequently settle down

Deltas are always associated with water and because of flat

topography, the water table occurs within few meters of the ground surface

The groundwater table elevations in deltas are fairly constant,

reflecting the elevation of the nearby water body

There is always salt water intrusion into the fresh groundwater body

from the oceans. The extent of intrusion depends upon the difference in

elevation between groundwater table in the delta and the ocean surface as well

as the nature of the delta


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Coastal Plain DepositsCoastal Plain Deposits

Coastal plains are found all over the world as unconsolidated sediments, boundedCoastal plains are found all over the world as unconsolidated sediments, boundedon the continental sides by a highland such as cliff, reef, hill etc. and spread on theon the continental sides by a highland such as cliff, reef, hill etc. and spread on themarine side by a shore line from a surface water body, either a lake or oceanmarine side by a shore line from a surface water body, either a lake or ocean

Coastal plains include deposits of both continental and marine origin. Close to theCoastal plains include deposits of both continental and marine origin. Close to thefoothill of highlands continental deposits predominates gradually giving place tofoothill of highlands continental deposits predominates gradually giving place tomarine deposits seawardmarine deposits seaward

With regular tidal fluctuations these two types of deposit become intercalatedWith regular tidal fluctuations these two types of deposit become intercalated

The source of supply may be rives, ice, wind and coastal erosionThe source of supply may be rives, ice, wind and coastal erosion

Fresh groundwater occurs in some areas of the coastal plain where there are noFresh groundwater occurs in some areas of the coastal plain where there are novalley deposits in the hinterlands. This water is provided directly from the rainfall andvalley deposits in the hinterlands. This water is provided directly from the rainfall andindirectly from inflow of water from the adjacent hillsindirectly from inflow of water from the adjacent hills

coastal plain formations can acts as a groundwater reservoir by hloding the freshcoastal plain formations can acts as a groundwater reservoir by hloding the freshwater supplies slightly above sea level and the salt water tablewater supplies slightly above sea level and the salt water table

S d D


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Sand DunesIn physical geography, a dune is a

hill of sand built by aeolian

processes.

Dunes are subject to different

forms and sizes based on their

interaction with the wind.

Most kinds of dune are longer on

the windward side where the sandis pushed up the dune, and a

shorter "slip face" in the lee of the

wind.

The "valley" or trough betweendunes is called a slack.

A "dune field" is an area covered

by extensive sand dunes. Large

dune fields are known as ergs

Direction of wind flow


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Dunes are accumulated wind deposits consisting of sand size

particles. The unequal side slopes reflect the dominant wind direction

They are the most isotropic and homogeneous deposits in nature

Sand dune materials are of uniform size and allow rapid

infiltration and percolation of rain fall. The geological layers underlying

the sand dunes may offer suitable groundwater supplies


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Glacial Deposits

Any deposit that owes its origin

more or less directly to the grinding action

of glaciers is referred as glacial deposit

They provide poorly sorted porous

medium, which has clasts of many sizes

including boulders and therefore may

provide a potential source for groundwater,

for example: Northern U.S.A., Canada,

Europe deposits formed by continental

glaciers furnish significant water reservoir

The void ratio of the glacial

deposits are high at the till source but

decreases with the distance travel away

from

Much of the debris transported by

glaciers is either deposited near the down-

glacier margins or laid out as outwash

along the downstream course

Moraine


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Glacial Flow Path

Glaciers forms a V-shape valley

Glacial Deposits are of two types:

(1) Esker

(2) Kame


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Esker

Most eskers are believed to form inice-walled tunnels by streams which

flowed within and under glaciers.

After the retaining ice walls melt

away, stream deposits remain as long

winding ridges.

Eskers may also form above glaciers

by accumulation of sediment in

supraglacial channels, in crevasses,

in linear zones between stagnant

blocks, or in narrow embayment atglacier margins.

Eskers form near the terminal zone of

glaciers, where the ice is not moving

as fast and is relatively thin

Terraces along ridges of glacifluvial material laying roughly parallel to the

direction offormer ice flow are usually termed as Eskers.


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The rate of plastic flow and melting

of the basal ice determines the size

and shape of the sub-glacial tunnel.

This in turn determines the shape,

composition and structure of anesker.

Eskers may exist as a single channel,

or may be part of a branching system

with tributary eskers.

They are not often found as

continuous ridges, but have gaps

that separate the winding segments.

The ridge crests of eskers are not

usually level for very long, and aregenerally knobby.

Eskers may be broad-crested or

sharp-crested with steep sides They

can reach hundreds of kilometers in

length.


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The concentration of rock debris in the ice and the rate at which sediment

is delivered to the tunnel by melting and from upstream transport

determines the amount of sediment in an esker.

The sediment generally consists of coarse-grained, water-laid sand and

gravel, although gravelly loam may be found where the rock debris is rich

in clay.

This sediment is stratified and sorted, and usually consists of

pebble/cobble-sized material with occasional boulders.


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Bed Rock

Glacier

Glacial fluvial Deposits

KAME

A kame is a geological feature, an irregularly shaped hill or mound composed

of sand, gravel and till that accumulates in a depression on a retreating glacier,

and is then deposited on the land surface with further melting of the glacier.

Kame terraces are frequently found

along the side of a glacial valley and

are the deposits of meltwater

streams flowing between the ice andthe adjacent valley side.

These kame terraces tend to look like

long flat benches, with a lot of pits

on the surface made by kettles.

They tend to slope downvalley with

gradients similar to the glacier

surface along which they formed,

and can sometimes be found paired

on opposite sides of a valley.


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Bed Rock

Glacier

Glacial fluvial Deposits

Usually forms both banks

of the valley

Their formation involves

two major steps

(1) During the existence of valley glacier, melt water streams run

along the sides of the valley building up lateral terraces

(2) With the disappearance of the glacier existing glacifluvial deposits

on both valley sides collapse to form kames


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Clastic sedimentary rocks are rocks

composed predominantly of broken pieces

or clasts of older weathered and eroded

rocks.

They recognize by their clastic texture

where nither chemical nor biological

precipitation nor accumulations of organic

material has been involved in their

formation.

Clastic sediments or sedimentary rocks are

classified based on grain size, clast and

cementing material (matrix) composition,

and texture.

Sedimentary Rocks

Clastic sedimentary rocks Non-Clastic sedimentary rocks

Clastic sedimentary rocks :

sedimentary rocks

F t d M di


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Fractured Medium

The fractures are defined as secondary structures in the form of planar

on non planar surface with in a rock mass along which there is no

cohesion.

Factures have developed as a result of pressure and temperature

differences during and/or after the formation of the rock.

Fractures occur chiefly in dense crystalline rocks.

Major fractures are supercapillary size and/or fed by tributary fractures

that are commonly capillary in size.

Fractures are referred to in terms of relative strength of the force

involved:

(1) Fault : Appreciable displacement has occurred in a fracture

(2) Joint : There is no noticeable displacement is seen


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Cause of Fracture:

Tectonic movement that cause the earth crust to deform

Change in rock volume due to the loss or gain of water,

Change in rock volume due to temperature differences, specially in

igneous rocks

Characteristics of Fracture:

The characteristics of the facture depends on the resistance offered by the

rock to the force involved.

For example: in hard rocks the fractures are extensive, large and dense

compared to those of soft rocks

The groundwater transmission characteristics of a fractured reservoir

depends on the width, roughness, continuity, spacing and filling of the

fractures and the kinematic viscosity of water.

K ti M di


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Karstic Medium

Karstic domain is a product of the chemical reactions between the rock and water.

It consists of sediments like limestone, dolomite, gypsum, halite and other soluble

rocks to constitute the reservoir.

Flow Channel in the Medium

Karstic formations are fully

developed in the humid and

semi-arid regions where thelakes are usually

interconnected with the

underlying solution-cavity

network

In the arid zones oases areformed within the karstic

reservoirs. The solution cavity

network transports the ground

water flow from the deep-lying

water-bearing formations

towards these water bodies


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Origin of Water

meteoric Connate Juvenile

Meteoric:

The most groundwater is

derived from the atmosphere

in the form of rainfall, snow,

hail, humidity etc. Water

of this type is referred toas meteoric water. It

takes part in Hydrological

cycle.


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It reaches to the earths

surface either infiltrateddirectly through porous,

fractured and Karstic

media or accumulates as

river, lakes or ponds fromwhich it reaches the

groundwater storage.

Water for domestic,

agricultural and industryuse is mainly from such

meteoric water


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Connate:

The water that was entrapped in the interstices of a sedimentary rockat the time of rock formation.

It is the fossil water that has been cut off the hydrological cycle for at

least an appreciable part of a geological period.

They may be either terrestrial or marine water.

It occurs at great depth. It has not undergone the present day

hydrological cycle.

It is rather salty.


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Juvenile:

This type of water is derived from igneous process with in thedepths of the earth.

It is not taken part in any of the hydrological cycle.

It can contribute unusually to the meteoric ground water it joins.


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Zones of Water

The subsurface water is divided into two major zones

depending on the physical occurrence of water

Soil Moisture Zone

Intermediate Zone

Capillary Zone

Saturated Zone(Void Spaces are filled with Water)

Unsaturated Zone: Void spaces are filled with water,

moisture and air Free exchange of air occur in this

zone Water in this zone is called

Vadose water Pressure of ground water is less

than atmospheric pressure

Saturated Zone:

Pressure of ground water is more

than atmospheric pressure

Un saturated Zone


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Un-saturated Zone

Soil Moisture Zone:

Helpful for leaving of plants.

Thick ness of soil-moisture zone depends upon the type of soil

and climate of the area

Deciding factors: soil suction and gravity

Intermediate Zone:

The water is bounded with the soil by the adhesive force

between soil and the water molecules

Capillary Zone :

The water is hold by the capillary forces acting against

gravity.

Groundwater Table


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Groundwater Table

Soil Moisture Zone

Intermediate Zone

Capillary Zone

Saturated Zone

(Void Spaces are filled with Water)

Pressure

+ve-ve

Dep

th

Groundwater Table

The sub-surface depth where the groundwater pressure is equal to the atmospheric

pressure

The water Table may change with season, topography and structural geology

When the earths slanting surface intersect the water table springs are generated

Some times they account for the base flow water levels in the water bodies


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Based on the geological conditions, hydrological conditions and the groundwater

pressure we divided the reserves into following categories:

Aquifer: A geological formation of group of formations or part of formation that

contains sufficient saturated permeable material to yield significant quantity of water

using a water well.

Aquiclude: This is a saturated geological formation which absorbs water slowly, but

does not transport it fast enough to yield a significant supply for a well.

Example: Clay layers

Aquifuge: A geological formation with non-interconnected openings or interstices is

called aquifuge. Neither it absorbs nor transmits water. It forms the base of the

aquifer.

Aquitard: Any geological formation that transmits water at a slower rate than an

aquifer. It is a transition between Aquifuge and Aquiclude.


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Aquifer

Unconfined Confined LeakyPerched

Aquifuge

Confined Aquifer

Aquitard

Unconfined Aquifer

Unsaturated Zone

Stream

Unconfined Aquifer:


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Unconfined Aquifer:

Groundwater table forms the upper

boundary of the saturation zone

They are subject to direct recharge fromthe infiltration, directly connected to the

hydrological cycle

Groundwater occurs at shallow depth,

therefore contaminated easily

Unsaturated Zone

Saturated Zone

Aquifige

Confined Aquifer:

It consists of three layers.

Pressure always above the atmosphericpressure

Any well drilled in a confined aquifer will

have water level elevation above the

aquifer

Unsaturated Zone

Saturated Zone

Aquifige

Groundwater Energy


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Groundwater Energy

Energy per unit volume is given by

'

2

2

1

PZ

g

vEs ++= Specific Volume

K.E. of Water(Velocity Head)

Potential Energy

(Elevation Head)

Pressure Energy(Pressure Head)

g ='

Total Energy

(Hydraulic Head)

Piezometric Head()

Groundwater Motion


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Darcys Law

1Z

'

1

P

'2

P

2Z

2

1

LQ

21

LKAQ

)( 21 =

It is an empirical Law.

Assumptions:

Groundwater moves continuously in a manner governed by established hydraulicprinciple under the influence of aquifers inherent and geometric features

Flow is steady and laminar, no temperature variation

gkK =


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Problem:

Rainfall at the rate 10mm/h falls on a strip of land 1km wide laying between two

parallel canals with 2m difference in their levels. It is underlain by a horizontalimpermeable datum at 10m below the water surface of the lower canal.

Assuming a permiability of 12m/d with vertical boundaries and all the filtered in to

the soil, compute the discharge per meter length into both of the canals.

Drainage Basin


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Drainage Basin

TributariesA drainage basin is an extent or area

of land where water from rain andmelting snow or ice drains downhill

into a body of water, such as a river,

lake, reservoir, estuary, wetland, sea

or ocean.

The drainage basin includes both the

streams and rivers that convey the

water as well as the land surfaces from

which water drains into thosechannels, and is separated from

adjacent basins by a drainage divide.

Watershed


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A watershed is a basin-like landform defined by highpoints and ridgelines

that descend into lower elevations and stream valleys. A watershed

carries water "shed" from the land after rain falls and snow melts.

Source of water:

1. Precipitation : in the form of rain or snow

2. Glacial Melt

Way of Water (Particularly the Precipitated water)

1. Infiltration : contribute to ground water, fountains

2. Surface runoff

Rain gauge data is used to measure total precipitation over a drainage basin, and there

diff t t i t t th t d t


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are different ways to interpret that data.

Arithmetic mean: If the gauges are many and evenly distributed over an area of uniform

precipitation, using the arithmetic mean method will give good results.

Thiessen polygon: In this method, the watershed is divided into polygons with the rain

gauge in the middle of each polygon assumed to be representative for the rainfall on the

area of land included in its polygon. These polygons are made by drawing lines between

gauges, then making perpendicular bisectors of those lines form the polygons.

Isohyetal method: This method involves contours of equal precipitation are drawn overthe gauges on a map. Calculating the area between these curves and adding up the

volume of water in each area.

R i f ll R ff A l iR i f ll R ff A l i


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Rainfall Runoff AnalysisRainfall Runoff Analysis

Surface runoff is the water flow that occurs

when soil is infiltrated to full capacity andexcess water from rain, melt-water, or other

sources flows over the land.

Runoff generation from rainfall over a catchment can be

assumed to depend on factors Atmospheric condition over the catchment (Temperature, humidity,

wind speed, ect.)

The surface cover (type, distribution, interception, take up,

evapotranspiration etc) Surface soil (type, permeability, porosity, etc)

Terrain (slope, surface texture, etc)

Geology (structure distribution, permeability, porosity,

groundwater levels, etc)

Generally the following processes are usually identified as


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Generally the following processes are usually identified as

taking place:

Saturated zone flow

(groundwater)

Unsaturated Zone

Saturated Zone

Aquifige

Evapotranspir

ation at the

surface

Surface infiltration (surface

cover, wetness of the soil)

Rainfall can not infiltrate locally

due to the intense nature of the

rainfall)

Overland flow

Unsaturated zone

flow (surface tension

of water, nature andstructure of the soil)

Hydrograph and the catchments characteristics


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The shape of the hydrograph depends on the characteristics of the catchment.

The major factors are

Shape of the catchment

Size of the catchment

Slope

rainfall intensity and duration

spatial distribution of rainfall

Shape of the Catchment


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Shape of the Catchment

Size of the Catchment:


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Naturally, the volume of runoff expected for a given rainfall input would be

proportional to the size of the catchment.

But this apart, the response characteristics of large catchment ( say, a large riverbasin) is found to be significantly different from a small catchment (like agricultural

plot) due to the relative importance of the different phases of runoff (overland flow,

inter flow, base flow, etc.) for these two catchments.

Further, it can be shown from the mathematical calculations of surface runoff on two

impervious catchments (like urban areas, where infiltration becomes negligible) andthe plane area are different.

Slope

Slope of the main stream cutting across the catchment and that of the valley sides or

general land slope affects the shape of the hydrograph.

Larger slopes generate more velocity than smaller slopes and hence can dispose off

runoff faster. Hence, for smaller slopes, the balance between rainfall input and the

runoff rate gets stored temporally over the area and is able to drain out gradually over

time. Hence, for the same rainfall input to two catchments of the same area but with

with different slopes, the one with a steeper slope would generate a hydrograph with

steeper rising and falling limits.

rainfall intensity and durationspatial distribution of rainfall


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Assume now that only area A1 receives rainfall

but the other areas do not, then since this

region is nearest to the catchment outlet, the

resulting hydrograph immediately rises. If the

rainfall continues for a time more than t, then

the hydrograph would reach a saturation equal

to re.A1, where re is the intensity of the

effective rainfall.

rainfall intensity and duration


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Assume now that a rainfall of constant

intensity is falling only within area A4,

which is farthest from the catchment

outlet. Since the lower boundary of A4

is the Isochrone III, there would be no

resulting hydrograph till time 3t.

If the rain continues beyond a time

4t, then the hydrograph would reach

a saturation level equal to re A4 wherere is the effective rainfall intensity.

The Unit Hydrograph


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The Unit Hydrograph The Unit Hydrograph (abbreviated asUH) of a drainage basin is

defined as a hydrograph ofdirect runoffresulting fromone unit ofeffective rainfallwhich isuniformly distributed over the basinat a

uniform rate during the specified period of time known as unittime or unit duration.

The unit quantity of effectiverainfall is generally taken as 1mmor 1cm and the outflowhydrograph is expressed by thedischarge ordinates.

The unit duration hour

(the unit duration cannot be morethan the time of concentration,which is the time that is taken by

the water from the furthest point ofthe catchment to reach the outlet. )

Unit hydrograph assumptions


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Effective rainfall should be uniformly distributed over the basin.( N rain gauges

spread uniformly over the basin, record almost same amount of rainfall during the

specified time)

Effective rainfall is constant over the catchment during the unit time.

The direct runoff hydrograph for a given effective rainfall for a catchment is always

the same irrespective of when it occurs. Hence, any previous rainfall event is not

considered. This antecedent precipitation is otherwise important because of itseffect on soil-infiltration rate, depressional and detention storage, and hence, on the

resultant hydrograph.

The ordinates of the unit hydrograph are directly proportional to the effective rainfall

hyetograph ordinate. Hence, if a 6-h unit hydrograph due to 1 cm rainfall is given,

then a 6-h hydrograph due to 2 cm rainfall would just mean doubling the unithydrograph ordinates. Hence, the base of the resulting hydrograph (from the start

or rise up to the time when discharge becomes zero) also remains the same.

Unit hydrograph limitations


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Unit hydrograph limitations

Under the natural conditions of rainfall over drainage basins, the assumptions of

the unit hydrograph cannot be satisfied perfectly.

In theory, the principle of unit hydrograph is applicable to a basin of any size.

However, in practice, to meet the basic assumption in the derivation of the unit

hydrograph as closely as possible, it is essential to use storms which are

uniformly distributed over the basin and producing rainfall excess at uniform rate.

The limit is generally considered to be about 5000 sq. km. beyond which thereliability of the unit hydrograph method diminishes.


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Rainfall runoff relation

Runoff is a complex interaction betweenprecipitation and landscape factors. Whilesome of these factors (e.g., land use andcover, topography, soil characteristics, and

hydrologic condition).

Land use : urban area, forest area, agricultural land, etc. Land cover: type of forest cover, type of agricultural land,

grass land etc?

Topography: mountainous area, plane land etc. Soil characteristics: type of soil (red soil, black soil etc.),

water bearing capacity

When runoff occurs ?Runoff occurs when parts of the landscape are saturated or impervious.


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p p p

Two runoff concepts include (i)infiltration-excessrunoffand

(ii) saturation excessrunoff

Infiltration-excess runoff

The infiltration-excess runoff paradigm assumes that overland flow occurs when therainfall intensity is greater than the infiltration rate at the surface soil. In this case thewater, in excess of that which infiltrates through the soil surface, flows across the soilsurface to nearby channels. This process is also termed as Hortonian runoff.

When it occurs?

Firstly, rain must fall on the landscape with an intensity or rate in excess of the dynamicpermeability of the surface soil.

Secondly, the duration of rainfall must last longer than the time required to saturate thesurface.

Where it occurs?

Infiltration excess runoff occurs less frequently (Freeze, 1972) except from (1) disturbedor poorly vegetated areas that usually have a sub-humid or semiarid climate (Wolock,1993),

(2) Clay dominated surface soils,

(3) Watersheds where bedrock surfaces are exposed, and (4) Urban impervious surfaces.

Saturation excess runoff


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Saturation-excess runoff

Where the soil surface is saturated and any further rainfall, even at low

intensities, generates runoff that contributes to streamflow. This moredominant process is termed as saturation-excess runoff generation.

A rise in the water table occurs because of a large infiltration rate of waterinto the soil and down to the saturated subsurface (Wolock, 1993).

The variable spatial extent of the landscape saturated from below thatfluctuates dynamically with watershed wetness is termed the variable sourcearea (Freeze and Cherry, 1979).

Variable source areas can arise from direct rainfall on the landscape or fromreturn flow of subsurface water to the surface (Dunne and Black, 1970).

Saturated surface areas typically develop near existing stream channels andin depressions or hollows (Dunne et al., 1975) and expand as more waterinfiltrates and moves downslope as saturated subsurface flow.

Runoff Model


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A runoff model is a mathematical model describing the rainfall - runoff relations of a

rainfall catchment area, drainage basin orwatershed.

More precisely, it produces the surface runoff hydrograph as a response to a rainfall

hydrograph as input. In other words, the model calculates the conversion of rainfall into

runoff.

Linear Reservoir

S is the water storage with unit [L]

A is the constant reaction factoror

response factorwith unit [1/T]

Q is the runoffordischarge

Q=A.S ,

where S in mm and T in hr, day


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R is the effective rainfallorrainfall excess

orrecharge

dS is a differential or small increment of S

dT is a differential or small increment of T

dT

dSQR +=

dT

dSASR +=

For zero recharge: S=C*exp(-At)

If Q1 and Q2 are the discharge at time t1 and t2, then we can express

)1()()(

121212 ttatta eReQQ

+=

Rainfall- Runoff Relation


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Rainfall Runoff Relation

The rainfall & runoff are related througha number called runoff curve number

(also called a curve numberor simplyCN). It is an empirical parameter used in

hydrology for predicting direct runoff or

infiltration from rainfall excess

The curve number method

estimates runoff depth or volume,

Q, from rainfall depth or volume, P

Principle: Conservation of of water in a

watershed

Soil conservation services (SCS) of USA later known as

Natural Resources Conservation Service


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The runoff in the watersheds is given by the relation:


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The runoff in the watersheds is given by the relation:

Compute the Surface Storage (S)

S = (1000 / CN) 10S = (1000 / 61 ) 10 = 6.393 Inches

Compute the Initial Abstraction:

Ia = 0.2 x SIa = 0.2 x 6.393 = 1.279 Inches

Compute the runoff in Watershed Inches:

Q = (P Ia)2 / (P Ia + S)

Q = (5.00 1.279)2 / (5.00 1.279 + 6.393)

Q = 1.369 Inches (Remember the original P=5.00 Inches)

Compute the Runoff Volume:

V = [1.369 In / (12 In / Ft)] x 250 Ft x 350 Ft

=

V = 9983 CF


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Supply of Water ResourcesSupply of Water Resources

Fig. 15-2 p. 307Fig. 15-2 p. 307

FreshwaterFreshwater Readily accessible freshwaterReadily accessible freshwater

Biota

0.0001%

Biota

0.0001%

Rivers0.0001%Rivers

0.0001%

Atmospheric

water vapor

0.0001%

Atmospheric

water vapor0.0001%

Lakes

0.0007%

Soil

moisture

0.0005%

Groundwater

0.226%

Groundwater

0.226%

Ice caps

and glaciers

0.76%

0.014%0.014%

Ground Water


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Ground Water

Evaporation and transpiration

Evaporation

Stream

Infiltration

Water tableInfiltration

Unconfined aquifer

Confined aquifer

Lake

Well requiring a pump

Flowing

artesian well

Runoff

Precipitation

Confined

Recharge Area

Aquifer

Less permeable material

such as clay Confirming permeable rock layer


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Water Resources

Over the last century Human population has increased 3x

Global water withdrawal has increased 7x

Per capita water withdrawal has increased 4x

About one-sixth of the worlds people dont have

easy access to safe water

Most water resources are owned by governments

and are managed as publicly owned resources


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Kinds of Water Pollution

Inorganic Pollutants

Organic Pollutants

Biologic Pollutants


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Inorganic Pollutants

3 groups 1) Produce no heavlth effects until a threshold

concentration is exceedede.g., NO3ook at ,

50mg/liter; at higher levels: methaemoglobinaemia

2) No thresholde.g.genotoxic substances:

some natural and synthetic organic compounds,

microorganic compunds, some pesticides, arsenic

3) Essential to diets: F, I, Seabsence causesproblems, but too much also causes problems

Inorganic Trace Contaminants


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Inorganic Trace Contaminants

Mercurymethyl Hg and dimethyl Hg in fish

Lead Radionuclides

Phosphatesmostly a result of sewage outflow and phosphate detergent

Nitratessewage and fertilizers

Organic Pollutants

Three classes of compounds

Pesticides and Herbicides

Materials for common household and industrial useMaterials for industrial use

Groundwater ContaminationGroundwater Contamination


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Groundwater ContaminationGroundwater Contamination

Disolved in the water or carried by water by suspensionDisolved in the water or carried by water by suspension

Source of PolutionSource of Polution

Environmental:Environmental: (1) Carbonate rocks(1) Carbonate rocks

(2) Sea water intrusion(2) Sea water intrusion

Domestics:Domestics: Percolation from septic tankPercolation from septic tank

Artificial recharge of aquifers by sewage water, contains biologicalArtificial recharge of aquifers by sewage water, contains biological

contaminants (bacteria and Virus)contaminants (bacteria and Virus)

Industrial:Industrial:

Sewage disposal system serves both industrial and residential areasSewage disposal system serves both industrial and residential areas Presence of Heavy metals, radioactive metals, etc.Presence of Heavy metals, radioactive metals, etc.

AgriculturalAgricultural Groundwater pollution due to the fertilizers, salts, pesticides, etc.Groundwater pollution due to the fertilizers, salts, pesticides, etc.


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Monitoring water quality

Number of colonies of fecal coliform

bacteria

Bacterial source tracking (BST)

Measure biological oxygen demand (BOD)

Chemical analysis

Indicator speciesGenetic development of indicator

organisms

Types, Effects and Sources of WaterTypes, Effects and Sources of Water


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yp ,

Pollution

yp

Pollution

Point sourcesPoint sources

Nonpoint sources

Nonpoint sources

Water qualityWater quality

Fig. 22-3 p. 494Fig. 22-3 p. 494

Point and Nonpoint Sources


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Point and Nonpoint Sources

NONPOINT SOURCES

Urban streets

Suburbandevelopment

Wastewatertreatmentplant

Rural homes

Cropland

Factory

Animal feedlot

POINTSOURCES

Fig. 22-4 p. 494

Solutions: Preventing and ReducingSolutions: Preventing and Reducing


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g g

Surface Water PollutionSurface Water Pollution

Nonpoint SourcesNonpoint Sources Point SourcesPoint Sources

Reduce runoffReduce runoff

Buffer zone

vegetation

Buffer zone

vegetation

Reduce soil erosionReduce soil erosion

Clean Water ActClean Water Act

Water Quality ActWater Quality Act

Pollution of Lakes


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EutrophicationEutrophication

G d P ll i CG d t P ll ti C


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Groundwater Pollution: CausesGroundwater Pollution: Causes

Low flow rates

Low flow rates

Few bacteria

Few bacteriaCold temperaturesCold temperatures

Coal stripmine runoff

Pumpingwell

Waste lagoon

Accidentalspills

Groundwaterflow

Confined aquifer

Discharge

Leakage from faultycasing

Hazardous waste injection well

Pesticides

Gasolinestation

Buried gasolineand solvent tank

Sewer

Cesspoolseptic tank

De-icingroad salt

Unco

nfine

dfres

hwate

raqu

ifer

Confi

nedf

reshw

atera

quife

r

Water pumpingwell Landfill

Low oxygenLow oxygen

Fig. 22-9 p. 502

GG d t P ll ti P ti


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Groundwater Pollution PreventionGroundwater Pollution Prevention

Monitor aquifers Monitor aquifers

Leak detection systems Leak detection systems

Strictly regulating hazardous waste disposal Strictly regulating hazardous waste disposal

Store hazardous materials above ground Store hazardous materials above ground

Find less hazardous substitutes Find less hazardous substitutes

Concept of watershed managementConcept of watershed management


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p gp g

Watershed managementis the process of creating and implementing plans, programs,

and projects to sustain and enhance watershed functions that affect the mankind

It implies, the judicious use of all the resources i.e. land, water, vegetation in an area

for providing an answer to alleviate drought, moderate floods, prevent soil erosion,

improve water availability and increase food, fodder, fuel and fiber on sustained basis.

Watershed to achieve maximum production with minimum hazard to the natural

resources and for the well being of people.

Principles of Watershed Management


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The main principles of watershed management based on resource conservation, resource

generation and resource utilization are

Utilizing the land based on its capability

Protecting fertile top soil

Minimizing silting up of tanks, reservoirs and lower fertile land

Protecting vegetative cover throughout the year In situ conservation of rain water Safe diversion of gullies and construction of check dams for in creasing ground

water recharge In creasing cropping intensity through inter and sequence cropping. Alternate land use systems for efficient use of marginal lands. Water harvesting for supplemental irrigation.- Maximizing farm income through agricultural related activities such as dairy,

poultry, sheep, and goat forming.- Improving infrastructural facilities for storage, transport and agricultural

marketing,- Improving socio - economic status of farmers

Objectives of Watershed Management

The term watershed management is nearly synonymous with soil and water conservation


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The term watershed management is nearly synonymous with soil and water conservation

ith the difference that emphasis is on flood protection and sediment control besides

maximizing crop production.

The basic objective of watershed management is thus is thus meeting the problems ofland and water use, not in terms of any one resource but on the basis that all the

resources are interdependent and must, therefore, be considered together.

The watershed aims, ultimately, at improving standards of living of common people in the

basin by increasing their earning capacity, by offering facilities such as electricity, drinking

ater, irrigation water, freedom from fears of floods, droughts etc.

The overall objectives of watershed development programmers may be outlined as:

Recognition of watersheds as a unit for development and efficient use of land according

their land capabilities for production,

Flood control through small multipurpose reservoirs and other water storage structures at

the head water of streams and in problem areas,

Adequate water supply for domestic, agricultural and industrial needs.

Abatement of organic, inorganic and soil pollution,

Efficient use of natural resources for improving agriculture and allied occupation so as to

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Environmental Science -1_1