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How to harness the water potential of a river optimally?

Headworks :

Any hydraulic structure which supplies water to the off-taking canal

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HeadworksHeadwork

1. Storage headwork.

2. Diversion headwork.

Storage headwork : the construction of a dam on the river. to store water during the period of excess supplies

to releases it when demand overtakes available supplies

Diversion headwork :

serves to divert the required supply to canal from the river.

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Storage headworks Dams) Impervious barrier the river to store water in the upstream side

(reservoir) the storage of water

reduce the impact of a flood down stream

to use the water beneficially in future

Hydropower

Irrigation

Water for domestic consumption

Drought control

For navigational facilities

capacity of reservoir : height of the dam and the shape of the river

valley on the up stream

Spillways: to discharge excess flood water

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DAMS

Principal components of a storage dam :

storage a structure to obstruct river flow,

a spillway for discharging excess flood water

outlets for allowing the storage water to be with drawn for

some useful purpose or to flow downstream at a regulated

quantity

Dam engineering brings together a range of disciplines,

like structural, hydraulics and hydrology, geotechnical,

environmental etc

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DAMS : Choosing a suitable location of dam

Topography:

i. a gorge which is most narrow, which would require minimum

quantities of dam construction material.ii. the volume of the water that may be able to store in the reservoir

behind the dam

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Geotechnical suitability (foundations)i. foundation should be geo technically sound to sustain the

high stresses due to

i. the self weight of the structure,

ii. water pressure of the reservoir

iii. and earth quake vibration induced forces at the dam body and the

water in the reservoir

ii. No dams should be erected across a fault

iii. Formations in which alternate hard and soft rocks may be

avoided

iv. Dams built on one uniform formation is preferred

DAMS : Choosing a suitable location of dam

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Submergence possibilities

Availability of a suitable spillway site

Hydrologic adequacy : it should satisfy1. The average quantity of water available in the river through out

year.

2. The minimum flow of the river

3. The maximum flow that has been recorded and estimates of whatmight occur in future.

Reservoir : deep reservoir is preferred over shallow one to minimize cost of submerged land per unit capacity, evaporation losses

and weed growth

Possibility of river diversion during construction

Sedimentation possibilities

Communication

Locality

DAMS : Choosing a suitable location of dam

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DAMS : CLASSIFICATION

Based on use:i. Storage dams

ii. Diversion dams

iii. Detention dams :

Water spreading dams / dikes

Debris dam

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DAMS : CLASSIFICATION

Based on hydraulic structure:

i. Non overflow dams

ii. Overflow dams

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DAMS : CLASSIFICATION

Based on materials:

i. Rigid dams

i. Gravity dam (masonry / concrete)

ii. Arch dam (masonry / concrete)

iii. Buttress dam (concrete)

iv. Steel dam

v. Timber dam

ii. Non-rigid dams

i. Earth fill damii. Rock fill dam

iii. Combined earth and rock fill dam

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Embankment ams constructed of natural materials excavated or obtained from the

vicinity of the dam site

The natural fill materials are placed and compacted without the

addition of any binding agent

Earth-fill or earthen embankmentsuse compacted soil for

constructing the bulk of the dam volume.

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Rock-fill embankments

impervious core of compacted earth fill or a slender concrete

or bituminous membrane

bulk of the dam volume is made of coarse grained gravels,

crushed rocks or boulders.

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Gravity dams

External forces are resisted by weight of the dam

Masonry or concrete

Permanent

Less maintenance

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The basic shape of a concrete gravity dam is triangular in section

A gravity dam should also have an appropriate spillway for

releasing excess flood water

energy dissipating structure : stilling basin

spillway is provided with a gate

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Advantages (over earth dams)

Strong and stable than earth dams

Suitable for across gorges having very steep side slope

Can be used as an overflow spillway crest

Suited for the areas having heavy downpour Least maintenance

No sudden failure

Deep-set sluices can be used to retard sedimentation in

reservoir

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Disadvantages

Sound rock foundation, impermeable rock strata

High initial cost

More time to construct

Skilled labour Difficult to allow subsequent rise in height

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ARCH DAMS

Curved in plan

Carries major part of the water load horizontally to the abutments (arch

action ) The balance of the water load is transferred to the foundation by cantilever

action

Strong side walls

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Advantages (over gravity gravity dams)

Suited for gorges where length is small in proportion toheight

Section is less when compared with gravity dam of same

height

Less material

Less base width

Limited problems due to uplift pressure

Can be constructed on moderate foundations

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Disadvantages

Skilled labour

More time

Very strong abutments

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BUTTRESS DAM

buttresses dividing the space into a number of spansm

Multiple arch type

Deck type buttress dam

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Advantages (over gravity dam)

Less massive

Less material

Less foundation pressure, can be constructed on moderate

foundations

Water load acts normal to deck: vertical components

stabilizes dam against overturning and sliding

Subsequent raising of height is posiible

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Disadvantage

Skilled labour

Deterioration of upstream concrete surface is fatal

More susceptible to damage

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Gravity dam: Structure

Heel

Gallery

Toe

Spillway(inside dam)

Crest

NWL

Normal

water level

MWL

Max. level

Free boardSluice way

Upstream Down stream

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Heel: contact with the ground on the upstream side

Toe: contact on the downstream side

Abutment: Sides of the valley on which the structure of the dam rest

Galleries: small rooms like structure left within the dam for checkingoperations.

Diversion tunnel: Tunnels are constructed for diverting water before theconstruction of dam. This helps in keeping the river bed dry.

Spillways: It is the arrangement near the top to release the excess water of thereservoir to downstream side

Sluice way: An opening in the dam near the ground level, which is used toclear the silt accumulation in the reservoir side.

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GRAVITY DAM : Forces

Water pressure

Weight of dam

Uplift pressure

Earth quake pressure Ice Pressure

Wave Pressure

Silt Pressure

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GRAVITY DAM : Failure Overturning

Sliding

Compression / crushing

Tension

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Safety against overturning

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safety against sliding

FS against sliding = actual coeft of friction / sliding factor

Sliding factor = tan = H/ (V U)

FS = /tan

Greater than 1

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Safety against compression and tension

Normal stress =Direct stress + Bending stress

Direct stress =FV/b*1

Bending stress = 6

FV.e/b2