DIVERSION DIVERSION HEAD WORKHEAD WORK

COMPONENTSCOMPONENTS

DIVERSION HEAD WORK.DIVERSION HEAD WORK.

The works which are constructed at The works which are constructed at the head of the canal in order to the head of the canal in order to divert the river towards the canal so divert the river towards the canal so as to ensure a regulated continuous as to ensure a regulated continuous supply of silt free water with a supply of silt free water with a certain minimum head in to the certain minimum head in to the canal are known as DIVERSION canal are known as DIVERSION HEAD WORK.HEAD WORK.

Difference between weir Difference between weir and barrageand barrage

If the major part or the entire If the major part or the entire ponding of water is achieved by a ponding of water is achieved by a crest and a smaller part or nil part is crest and a smaller part or nil part is achieved by the shutters then this achieved by the shutters then this barrier is known as WEIR.barrier is known as WEIR.

If most of the ponding is done by the If most of the ponding is done by the gates and a smaller or nil part of it is gates and a smaller or nil part of it is done by the raised crest then the done by the raised crest then the barrier is known as BARRAGE barrier is known as BARRAGE

Difference between Gravity Difference between Gravity and and

Non Gravity weir Non Gravity weir When the weight of the weir (i.e its body When the weight of the weir (i.e its body

and floor) balances the uplift pressure and floor) balances the uplift pressure caused by the head of the water seeping caused by the head of the water seeping below the weir it is called GRAVITY WEIR.below the weir it is called GRAVITY WEIR.

If the weir floor is designed continuous with If the weir floor is designed continuous with the divide piers as reinforced structure the divide piers as reinforced structure such that the weight of concrete slab such that the weight of concrete slab together with weight of divide piers keep together with weight of divide piers keep the structure safe against the uplift then the structure safe against the uplift then the structure may be called as NON the structure may be called as NON GRAVITY WEIR GRAVITY WEIR

COMPONENTS OF COMPONENTS OF DIVERSION HEAD WORKDIVERSION HEAD WORK

Head work consists of following componentsHead work consists of following components1.1. Weir ProperWeir Proper2.2. Under sluicesUnder sluices3.3. Divide wallDivide wall4.4. River training works such as marginal River training works such as marginal

bunds, guide banks, gryones etcbunds, guide banks, gryones etc5.5. Fish ladderFish ladder6.6. Canal Head regulatorCanal Head regulator7.7. Weir ancillary works such as Weir ancillary works such as

shutter,gates,etcshutter,gates,etc8.8. Silt regulation worksSilt regulation works

Diversion weir and their Diversion weir and their typestypes

Diversion weir or an anycut or an intake weir is a raised Diversion weir or an anycut or an intake weir is a raised pucca structure with or without shutters and laid pucca structure with or without shutters and laid across the river width.across the river width.

Features of Diversion head workFeatures of Diversion head worka)a) Height of the weir crest may be upto 9 m or soHeight of the weir crest may be upto 9 m or sob)b) Height of the shutter over the weir crest seldoms exceeds 1.2m Height of the shutter over the weir crest seldoms exceeds 1.2m

or so.or so.c)c) Weirs usually aligned right angle to the direction of main Weirs usually aligned right angle to the direction of main

current which ensure lesser length,better dicharging capacity current which ensure lesser length,better dicharging capacity and lesser cost it is commonly used when the river bed is sandy and lesser cost it is commonly used when the river bed is sandy or silty.or silty.

d)d) For obtaining more and better foundation weir sometimes For obtaining more and better foundation weir sometimes aligned in oblique angle . Though it is costlier and of greater in aligned in oblique angle . Though it is costlier and of greater in length,less discharging capacity it is used where river bed is length,less discharging capacity it is used where river bed is made up of gravel or shingle which would otherwise enter the made up of gravel or shingle which would otherwise enter the head regulator of the main canal.head regulator of the main canal.

TYPES OF WEIRSTYPES OF WEIRS

Weirs are divided into three classesWeirs are divided into three classes Vertical drop weir Vertical drop weir Sloping Weir a ) Masonry or Sloping Weir a ) Masonry or

concrete slope weir b ) Dry stone concrete slope weir b ) Dry stone slope weirslope weir

Parabolic weirParabolic weir

Masonry weirs with Masonry weirs with vertical dropvertical drop

• This type of weir consist of horizontal floor and a This type of weir consist of horizontal floor and a masonry crest with vertical or nearly vertical masonry crest with vertical or nearly vertical downstream face.downstream face.

• Raised masonry crest does the maximum Raised masonry crest does the maximum ponding of water but a part of it is usually done ponding of water but a part of it is usually done by shutters at the top of the crest. The shutter by shutters at the top of the crest. The shutter can be dropped during floods so as to reduce the can be dropped during floods so as to reduce the afflux by increasing the water way opening.afflux by increasing the water way opening.

• To safe guard scoring action launching aprons To safe guard scoring action launching aprons are provided both at upstream and D/S end.are provided both at upstream and D/S end.

• A graded inverted filter is provided to relieve A graded inverted filter is provided to relieve uplift pressures.uplift pressures.

CONCRETE WEIR WITH SLOPING D/S GLACISCONCRETE WEIR WITH SLOPING D/S GLACIS Sheet piles of sufficient depth are driven at the Sheet piles of sufficient depth are driven at the

ends of U/s and D/s floor and sometimes an ends of U/s and D/s floor and sometimes an intermediate piles is provided to dissipates the intermediate piles is provided to dissipates the energy formed due to hydraulic jump on the D/s energy formed due to hydraulic jump on the D/s sloping glacissloping glacis

This type of weir is provided on permeable This type of weir is provided on permeable foundations. foundations.

Rock fill weirs with sloping apronRock fill weirs with sloping apronIt is also called as Dry stone slope weir.It is also called as Dry stone slope weir.

It is suitable for fine sandy foundations It is suitable for fine sandy foundations U/s and D/s rockfill laid in the form glacis.U/s and D/s rockfill laid in the form glacis.

Causes of failures of Causes of failures of weirs weirs

PIPINGPIPING Rupture of floor due to upliftRupture of floor due to uplift Rupture of floor due to suction Rupture of floor due to suction

caused by standing wave caused by standing wave Scour on the U/s and D/s of the weir.Scour on the U/s and D/s of the weir.

Causes of Failure of weirs Causes of Failure of weirs and their remediesand their remedies

Piping :Piping : Water seeps under the base of the Water seeps under the base of the weir founded on permeable soils . When the weir founded on permeable soils . When the flow lines emerge out at the D/s end of the flow lines emerge out at the D/s end of the impervious floor of the weir, the hydraulic impervious floor of the weir, the hydraulic gradient may exceed. With the removal of the gradient may exceed. With the removal of the surface soil there is further concentration of surface soil there is further concentration of flow lines resulting depression and more soil is flow lines resulting depression and more soil is removed. This process of erosion thus removed. This process of erosion thus progressively works backwards towards progressively works backwards towards upstream and results in the formation of a upstream and results in the formation of a channel or pipe underneath the floor of the channel or pipe underneath the floor of the weir causing failure.weir causing failure.

RemediesRemedies

i) Providing sufficient length of i) Providing sufficient length of impervious floor so that path of impervious floor so that path of percolation is increased.percolation is increased.

ii) Providing pile at the ii) Providing pile at the downstream ends.downstream ends.

Rupture of floor due to uplift :Rupture of floor due to uplift : If the If the weight of the floor is insufficient to weight of the floor is insufficient to resist uplift pressure the floor may resist uplift pressure the floor may burst and effective length of impervious burst and effective length of impervious floor is reduced and finally effective floor is reduced and finally effective length reduced.length reduced.Remedies Remedies i) Providing impervious floor i) Providing impervious floor of sufficient length and appropriate of sufficient length and appropriate thickness ii) Providing pile at the U/s thickness ii) Providing pile at the U/s end so that uplift pressure to the d/s is end so that uplift pressure to the d/s is reducedreduced

Rupture of floor due to suction caused by Rupture of floor due to suction caused by standing wavestanding wave The standing wave or The standing wave or hydraulic jump formed at the D/s of the hydraulic jump formed at the D/s of the weir causes suction which is also acts in weir causes suction which is also acts in the direction of uplift pressure. If the the direction of uplift pressure. If the floor thickness is insufficient it may floor thickness is insufficient it may rupturerupture

REMEDIES :REMEDIES : i) i)Providing additional thickness of floor to Providing additional thickness of floor to counterbalance the extra pressure due to standing counterbalance the extra pressure due to standing wave.wave.

ii) Constructing the floor thickness in one concrete ii) Constructing the floor thickness in one concrete mass instead of in masonry layers.mass instead of in masonry layers.

SCOUR ON THE U/s AND D/s OF THE WEIR.SCOUR ON THE U/s AND D/s OF THE WEIR.When the natural waterway of a river is When the natural waterway of a river is

contracted the water may scour the bed both contracted the water may scour the bed both at U/s and D/s of the structure. The scour at U/s and D/s of the structure. The scour holes so formed may progress towards the holes so formed may progress towards the structure causing failure.structure causing failure.

Remedies :Remedies : Taking piles at upstream and Taking piles at upstream and downstream ends of the impervious floor downstream ends of the impervious floor much below the calculated scour level.much below the calculated scour level.

Providing suitable length and thickness of Providing suitable length and thickness of launching apron at U/s and D/s sides so that launching apron at U/s and D/s sides so that stones of the aprons may settle in the scour stones of the aprons may settle in the scour holes.holes.

AFFLUX AND POND AFFLUX AND POND LEVELLEVEL

Afflux – The rise in the maximum flood Afflux – The rise in the maximum flood level (HFL) upstream of the weir level (HFL) upstream of the weir caused due to the construction of the caused due to the construction of the weir across the river is called afflux.weir across the river is called afflux.

Pond Level – The water level required Pond Level – The water level required in the under sluice pocket upstream of in the under sluice pocket upstream of the canal head regulator so as to feed the canal head regulator so as to feed the canal with its full supply is known the canal with its full supply is known as Pond Level.as Pond Level.

Under sluice or Scouring Under sluice or Scouring SluiceSluice Functions of under - sluice Functions of under - sluice

It helps in regulating less turbulent pocket of water near It helps in regulating less turbulent pocket of water near the canal head regulatorthe canal head regulator

As the crest level of the under sluice pocket is at low level As the crest level of the under sluice pocket is at low level than the crest level of the weir a deep channel develops towards than the crest level of the weir a deep channel develops towards this pocket which helps in bringing low dry weather discharge this pocket which helps in bringing low dry weather discharge towards this pocket.towards this pocket.

The under sluiced length of weir is divided into no.of ways by piers The under sluiced length of weir is divided into no.of ways by piers and separate gates are installed on these ways. and separate gates are installed on these ways. Each way thus be opened to any desired height by lifting its gate. Each way thus be opened to any desired height by lifting its gate. Each way can thus act as gate controlled opening and will help in Each way can thus act as gate controlled opening and will help in by passing the excess supplies to the downstream side of the river. by passing the excess supplies to the downstream side of the river.

These openings will also help in scouring and removing the These openings will also help in scouring and removing the deposited silt from the under-sluiced pocket and hence called the deposited silt from the under-sluiced pocket and hence called the SCOURING SLUICESSCOURING SLUICES

The crest level of the head regulator is The crest level of the head regulator is also kept higher than the crest level of also kept higher than the crest level of the under-sluices so that only silt free the under-sluices so that only silt free water is admitted into the canal through water is admitted into the canal through the head sluicesthe head sluices

Apart from the two important function Apart from the two important function served by the under-sluice they help in served by the under-sluice they help in passing the dry weather flow and low passing the dry weather flow and low floods without dropping the weir floods without dropping the weir shutters.shutters.

DIVIDE WALLDIVIDE WALL

The divide wall is a masonry or a concrete The divide wall is a masonry or a concrete wall constructed at right angles to the axis of wall constructed at right angles to the axis of the weir and separate the weir proper from the weir and separate the weir proper from under-sluice.under-sluice.

Divide wall extends on the upstream side Divide wall extends on the upstream side beyond the beginning of the canal head beyond the beginning of the canal head regulator and on the D/s side it extends up to regulator and on the D/s side it extends up to the end of the loose protection of under- the end of the loose protection of under- sluice.sluice.

The top width of divide wall is about 1.5m to The top width of divide wall is about 1.5m to 2.5m2.5m

DIVIDE WALLDIVIDE WALL Functions of divide wall Functions of divide wall a)a) It separates the under-sluices from the weir It separates the under-sluices from the weir

proper .Since crest level of the under-sluice is lower proper .Since crest level of the under-sluice is lower than of weir proper the two must be operated and than of weir proper the two must be operated and this is being done by Divide wall.this is being done by Divide wall.

b)b) It helps in providing a comparatively less turbulent It helps in providing a comparatively less turbulent pocket near the and thus to help in the entry of silt pocket near the and thus to help in the entry of silt free water into the canalfree water into the canal

c)c) Divide wall may keep the cross current away from Divide wall may keep the cross current away from the weir which causes vortices and deep scoursthe weir which causes vortices and deep scours

Divide walls can be designed as cantilever retaining Divide walls can be designed as cantilever retaining walls subjected walls subjected

silt pressure and water pressure from the under sluice silt pressure and water pressure from the under sluice side.side.

River training worksRiver training works

River training works are required River training works are required near the weir site in order to ensure near the weir site in order to ensure smooth and an axial flow of water and smooth and an axial flow of water and thus prevent the river from thus prevent the river from outflanking the works due to change outflanking the works due to change in its course.in its course.

The river training works reqd on a The river training works reqd on a canal head works are a) Guide bankscanal head works are a) Guide banks

b) Marginal bundsb) Marginal bunds c) Spurs or groynesc) Spurs or groynes

Types of river training Types of river training worksworks

Guide banks : Guide banks : Guide banks force the river into Guide banks force the river into restricted channel and thus ensuring a smooth and restricted channel and thus ensuring a smooth and an almost axial flow near the weir site.an almost axial flow near the weir site.

Marginal bunds : Marginal bunds : They are provided on the They are provided on the upstream side of the works in order to protect the upstream side of the works in order to protect the area from submergence due to rise in HFL caused area from submergence due to rise in HFL caused by afflux. by afflux.

Groyne : Groyne : Groynes are structures constructed Groynes are structures constructed transverse to the river and extend from the bank transverse to the river and extend from the bank into the river upto limit. Main purpose of Groyne into the river upto limit. Main purpose of Groyne are contracts a river channel to improve its depth, are contracts a river channel to improve its depth, protects the river bank, Silts up the area in the protects the river bank, Silts up the area in the vicinity by creating a slack flow and trains the flow vicinity by creating a slack flow and trains the flow along a certain course.along a certain course.

FISH LADDERFISH LADDER A structure which enables the fish to A structure which enables the fish to

pass upstream is called FISH LADDER. pass upstream is called FISH LADDER. It is a device by which flow energy can It is a device by which flow energy can be dissipated in such a manner as to be dissipated in such a manner as to provide smooth low velocity not provide smooth low velocity not exceeding 3 to 3.5m/sec.exceeding 3 to 3.5m/sec.

This object is generally accomplished by This object is generally accomplished by providing a narrow opening adjacent to providing a narrow opening adjacent to the divide wall and provide suitable the divide wall and provide suitable baffle walls so as to control flow baffle walls so as to control flow velocity.velocity.

CANAL HEAD CANAL HEAD REGULATORREGULATOR

A canal head regulator is a structure A canal head regulator is a structure constructed at the head of a canal taking off constructed at the head of a canal taking off from a reservoir behind a weir or a dam. A from a reservoir behind a weir or a dam. A head regulator may consist of number of spans head regulator may consist of number of spans separated by piers and operated by gates separated by piers and operated by gates similar to that provided in a barrage.similar to that provided in a barrage.

Functions Functions

a)To make the regulations of supply in the canal a)To make the regulations of supply in the canal easy.easy.

b)To control the silt entry in the canalb)To control the silt entry in the canal

c) To shut the river floodsc) To shut the river floods

Silt control devicesSilt control devices The entry of silt into a canal which takes off from a The entry of silt into a canal which takes off from a

head works can be reduced by constructing special head works can be reduced by constructing special works called silt control worksworks called silt control works

These works are classified into a) Silt ExcludersThese works are classified into a) Silt Excludersb) Silt Ejectors b) Silt Ejectors Silt Excluders : These are constructed on the bed of the Silt Excluders : These are constructed on the bed of the

river upstream of the head regulator thus cleaner river upstream of the head regulator thus cleaner water enters the head regulator and the silted water water enters the head regulator and the silted water enters the silt excluder.enters the silt excluder.

Silt Ejectors : Also called silt extractors these devices Silt Ejectors : Also called silt extractors these devices which extract the silt from the canal water after the which extract the silt from the canal water after the silted water has travelled a certain distance in the off silted water has travelled a certain distance in the off taking canal. They are present in the down stream taking canal. They are present in the down stream section of the canal.section of the canal.

BLIGH’S CREEP THEORYBLIGH’S CREEP THEORYThe design of the impervious floor or the apron is The design of the impervious floor or the apron is

directly dependent on the possibilities of directly dependent on the possibilities of percolation in the porous soil on which the apron percolation in the porous soil on which the apron is built.is built.

Bligh’S assumption Bligh’S assumption 1.1. The hydraulic slope or gradient is constant The hydraulic slope or gradient is constant

throughout the impervious length of the apronthroughout the impervious length of the apron2.2. The percolation of water to creep along the The percolation of water to creep along the

contact of the base profile of the apron with contact of the base profile of the apron with subsoil ,losing head enroute ,proportional to the subsoil ,losing head enroute ,proportional to the length’s of its travel. He designated travel as length’s of its travel. He designated travel as creep length which is sum of horizontal and creep length which is sum of horizontal and vertical length of creep.vertical length of creep.

H

d1 d2

l

A

B

D

E

Total creep length is L=2dTotal creep length is L=2d11+l+2d+l+2d22

If H is total loss of head the loss of If H is total loss of head the loss of head per unit length is creep c head per unit length is creep c =H/(2d=H/(2d11+l+2d+l+2d22))

= = H/LH/L

Cofficient of creep C =1/cCofficient of creep C =1/c

Design criteria ;Design criteria ;Safe against piping:The length of creep Safe against piping:The length of creep

should be sufficient to provide a safe should be sufficient to provide a safe hydraulic gradient hydraulic gradient

Thus safe creep length L= CHThus safe creep length L= CHSafe against Uplift pressure; let h’= Uplift Safe against Uplift pressure; let h’= Uplift

pressurepressureUplift pressure = wh’Uplift pressure = wh’Downad forces = t w GDownad forces = t w GHence Equating h’=tG Hence Equating h’=tG h’-t=t(G-1) hence t=h’/(G-1) h’-t=t(G-1) hence t=h’/(G-1) Providing factor t = 4/3 h’/(G-1)Providing factor t = 4/3 h’/(G-1)

LIMITATIONS BLIGH’S LIMITATIONS BLIGH’S THEORYTHEORY

Bligh’s made no distinction between Bligh’s made no distinction between horizontal and vertical creephorizontal and vertical creep

Bligh’s method hold goods so long as the Bligh’s method hold goods so long as the horizontal distance between the pile lines is horizontal distance between the pile lines is greater than twice their depth.greater than twice their depth.

Bligh did not explain the idea of exit gradient. Bligh did not explain the idea of exit gradient. Bligh’s makes no distinction between the Bligh’s makes no distinction between the

outer and inner faces of sheet piles or the outer and inner faces of sheet piles or the intermediate sheet pile.intermediate sheet pile.

Loss of head does not take place in the same Loss of head does not take place in the same proportion as creep length. proportion as creep length.

HEAD REGULATORHEAD REGULATOR

Regulate the supplies of the off taking Regulate the supplies of the off taking channel is called Head Regulator.channel is called Head Regulator.

Parent channel is regulated by Cross Parent channel is regulated by Cross regulator.regulator.

The distributaries head regulator is provided The distributaries head regulator is provided at the head of the distributaries and at the head of the distributaries and controls the supply entering the controls the supply entering the distributaries.distributaries.

A link between parent channel & distributing A link between parent channel & distributing channel is done by Head regulator.channel is done by Head regulator.

Cross Regulator : It is provided on the main Cross Regulator : It is provided on the main canal at the downstream of the off take to head canal at the downstream of the off take to head up the water level and to enable the offtaking up the water level and to enable the offtaking channel to draw the required supply.channel to draw the required supply.

Functions of distributary Head regulatorFunctions of distributary Head regulator1.1. They regulate or control the supplies to the off They regulate or control the supplies to the off

taking channeltaking channel2.2. They serve as a meter for measuring the They serve as a meter for measuring the

discharge entering discharge entering 3.3. They control silt entry in the off taking canalThey control silt entry in the off taking canal4.4. They help in shutting off the supplies when not They help in shutting off the supplies when not

needed in the offtaking canalneeded in the offtaking canal

Functions of Cross Functions of Cross regulatorregulator

1.1. The effective regulation of the whole canal The effective regulation of the whole canal system can be done with help of cross system can be done with help of cross regulator.regulator.

2.2. During the periods of low discharges in the During the periods of low discharges in the parent channel cross regulator raises water parent channel cross regulator raises water level of the U/s and feeds the offtake channel level of the U/s and feeds the offtake channel in rotationin rotation

3.3. It helps in closing the supply to the D/s of the It helps in closing the supply to the D/s of the parent channels for the purpose of repairsparent channels for the purpose of repairs

4.4. Bridges & communications works can be Bridges & communications works can be combined with it.combined with it.

CROSS DRAINAGE CROSS DRAINAGE WORKSWORKS

A cross drainage work is a structure A cross drainage work is a structure carryingcarrying

the discharge of a natural stream acrossthe discharge of a natural stream across

canal intercepting the stream.canal intercepting the stream.

1.1. C.D work carrying canal over the C.D work carrying canal over the drainagedrainage

2.2. C.D work carrying drainage over the C.D work carrying drainage over the canalcanal

3.3. C.D work admitting drainage water C.D work admitting drainage water into the canal.into the canal.

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5. Earthquake Zone : If the dam is so situated in an 5. Earthquake Zone : If the dam is so situated in an earthquake zone, its design must include the earthquake zone, its design must include the earthquake forces. Its safety should be ensured earthquake forces. Its safety should be ensured against increased stress induced by an earthquake against increased stress induced by an earthquake of worst intensity. The type of structures best suited of worst intensity. The type of structures best suited to resist earthquake shocks without danger are to resist earthquake shocks without danger are earthen dams and concrete gravity dams.earthen dams and concrete gravity dams.

6. Height of the dam: Earthen dams are usually not 6. Height of the dam: Earthen dams are usually not provided for heights more than 30 m or so. Hence provided for heights more than 30 m or so. Hence for greater heights, gravity dams are generally for greater heights, gravity dams are generally preferred.preferred.

7. Other considerations : Various other factors such 7. Other considerations : Various other factors such as life of the dam the width of the road way to be as life of the dam the width of the road way to be provided over the dam problem of the skilled labour provided over the dam problem of the skilled labour legal and aesthetic point must also considered befor legal and aesthetic point must also considered befor final decision taken,final decision taken,

Ridge canal or water shedRidge canal or water shed canal is aligned along a canal is aligned along a watershed and runs for most of its length on a watershed and runs for most of its length on a watershed. When a channel is on the watershed it can watershed. When a channel is on the watershed it can command areas on both banks and so a large area can command areas on both banks and so a large area can be brought under cultivation.be brought under cultivation.

Contour canal : A channel aligned nearly parallel to the Contour canal : A channel aligned nearly parallel to the contours of the country is called a contour canal. contours of the country is called a contour canal.

Side slope canal : It is channel aligned roughly at right Side slope canal : It is channel aligned roughly at right angles to the contours of the country and is neither on angles to the contours of the country and is neither on the water shed nor in the valley. Such channel would be the water shed nor in the valley. Such channel would be roughly parallel to the natural drainage of the country roughly parallel to the natural drainage of the country and hence does not intercept any cross drainage. and hence does not intercept any cross drainage. However it has very steep bed slope since the direction However it has very steep bed slope since the direction of the steepest slope of the ground is at right angles to of the steepest slope of the ground is at right angles to the contours of the country. the contours of the country.

Hydro power plantHydro power plant Hydropower plants may be classified on the basis Hydropower plants may be classified on the basis

of hydraulic characteristics into of hydraulic characteristics into Run off river plantsRun off river plantsStorage plantsStorage plantsPumped storage plantsPumped storage plantsTidal plantsTidal plants

Hydropower plants may be classified on the basis of Hydropower plants may be classified on the basis of operating head operating head

Low head scheme (< 15 m )Low head scheme (< 15 m )Medium head scheme ( 15 m to 60 m)Medium head scheme ( 15 m to 60 m)High head scheme ( > 60 m)High head scheme ( > 60 m)

Runoff river plants : Runoff river plants : Utilise minimum flow in river having no Utilise minimum flow in river having no

appreciable pondage on its upstreamappreciable pondage on its upstream A weir or barrgae is constructed to raise A weir or barrgae is constructed to raise

level of waterlevel of water Suitable for only on a perennial river having Suitable for only on a perennial river having

sufficient dry weather flowsufficient dry weather flow It has very limited storage so can be used to It has very limited storage so can be used to

meet hourly fluctuations of load.meet hourly fluctuations of load. When available discharge is more it can be When available discharge is more it can be

stored and can be used during peak hours stored and can be used during peak hours E.g Kotla power house in Nangal hydel plantE.g Kotla power house in Nangal hydel plant

Storage plants:Storage plants: It essentially have upstream storage reservoir of It essentially have upstream storage reservoir of

sufficient size so as to permit sufficient storage from sufficient size so as to permit sufficient storage from the monsoon to dry weather season so as to develop a the monsoon to dry weather season so as to develop a firm flow substantially more than the minimum firm flow substantially more than the minimum natural flow. natural flow.

Dams are constructed across the river and power Dams are constructed across the river and power house located at the foot of the damhouse located at the foot of the dam

When the power house is located near the dam as is When the power house is located near the dam as is generally in the low head installations ; it is called generally in the low head installations ; it is called concentrated fall concentrated fall

When the water is carried to the power house at When the water is carried to the power house at considerable distance through a canal ,tunnel or considerable distance through a canal ,tunnel or penstock it is called Divided fall developmentpenstock it is called Divided fall development

Pumped storage plant:Pumped storage plant: It generates power during peak hoursIt generates power during peak hours During off peak hours water is pumped During off peak hours water is pumped

back from tail water pool to head towerback from tail water pool to head tower Pumps run by some secondary powerPumps run by some secondary power primarily meant for assisting an existing primarily meant for assisting an existing

thermal plant or some other hydel plantthermal plant or some other hydel plant During peak hours water flows from the During peak hours water flows from the

reservoir to the turbine during off peak reservoir to the turbine during off peak hours the excess power available from hours the excess power available from other plant is utilised for pumping water other plant is utilised for pumping water from tail pool to head pool.from tail pool to head pool.

Tidal plantTidal plant Works on the principle that rise in sea water during high Works on the principle that rise in sea water during high

tide period and fall during the low ebb period.tide period and fall during the low ebb period. Water rises and fall twice a day,each fall cycle occupying Water rises and fall twice a day,each fall cycle occupying

about 12 hrs and 25 minutes.about 12 hrs and 25 minutes. Difference between high and low tide is utilised to generate Difference between high and low tide is utilised to generate

power.power. This is accomplished by constructing basin seperated from This is accomplished by constructing basin seperated from

ocean by a partition wall and installing turbines in opening ocean by a partition wall and installing turbines in opening through this wall.through this wall.

Water passes from the ocean to the basin during high tides, Water passes from the ocean to the basin during high tides, and thus running the turbines and generating electric power.and thus running the turbines and generating electric power.

During low tide, the water from the basin runs back to ocean During low tide, the water from the basin runs back to ocean which can be utilised to generate electric power, provided which can be utilised to generate electric power, provided special turbines which can generate power for either special turbines which can generate power for either direction of flow are installed.direction of flow are installed.

Rance power in france is an example Rance power in france is an example

Load factor is defined as ratio of the Load factor is defined as ratio of the average load over a certain period of time average load over a certain period of time to the peak load during the same period.to the peak load during the same period.

Load factor = Average load over a certain Load factor = Average load over a certain periodperiod

Peak load during that period.Peak load during that period.Annual load factor = Total yearly electrical units(kWh) Annual load factor = Total yearly electrical units(kWh)

producedproduced

Max power demand in kW x 365 x 24Max power demand in kW x 365 x 24

`̀ Capacity factor or Plant factor : It may be Capacity factor or Plant factor : It may be

defined as the ratio of average output for a defined as the ratio of average output for a given period of time to the plant capacity.given period of time to the plant capacity. Capacity factor=Average load (Over a given period of Capacity factor=Average load (Over a given period of time)time)

Plant capacityPlant capacity Utilisation factor = Water actually utilised for power Utilisation factor = Water actually utilised for power

station station

Water available in the riverWater available in the riverU.F = Max. power utilisedU.F = Max. power utilised

Max.power available.Max.power available.

Principal components of Principal components of Hydro electric schemeHydro electric scheme

A A hydroelectric development scheme hydroelectric development scheme ordinarily includes a diversion structure, ordinarily includes a diversion structure, a conduit (penstock) to carry water to the a conduit (penstock) to carry water to the turbines, turbines and governing turbines, turbines and governing mechanisms, generators, control and mechanisms, generators, control and switching apparatus, housing for the switching apparatus, housing for the equipment, transformers and equipment, transformers and transmission lines to distribution centres. transmission lines to distribution centres. In addition to these major components In addition to these major components trash racks at the entrance to penstock, trash racks at the entrance to penstock, canal and penstock gates a foreway a canal and penstock gates a foreway a surge tank and other appurtenances may surge tank and other appurtenances may be required.be required.

The major components of a hydroelectric The major components of a hydroelectric scheme are described below : scheme are described below :

1.1. The forewayThe foreway2.2. Intake structureIntake structure3.3. PenstockPenstock4.4. Surge tank or Surge chamber.Surge tank or Surge chamber.5.5. Hydraulic turbines.Hydraulic turbines.6.6. The power houseThe power house7.7. The Draft tubeThe Draft tube8.8. The tail race.The tail race.