Preporaki i Standardi Za SHPP

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For official use only DOC: WRD 22(577)CFeb 2012

BUREAU OF INDIAN STANDARDS

DraftIndian Standard

GUIDELINES FOR PLANNING AND DESIGN OF RIVER POWER HOUSES INTEGRATEDWITH BARRAGES PART 2 DESIGN (As part 2 of IS 14592)

(Not to be reproduced without the permission of BIS or used as standard)---------------------------------------------------------------------------------------------------------------------------

Last date for receipt of comments is 20-03-2012

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FOREWORD(Formal clauses of the foreword will be added later)

The criteria for the design of low-head river bed power houses integrated with barrages are to aconsiderable extent, similar to the criteria for the design of surface hydro power houses.However a few special considerations are necessary for such designs, which are covered inthis standard

The main points to be kept in mind are that, these power houses are sometimes founded onsoft pliable river bed material, in that case dynamic stability of the structure as per IS 1893:2002, susceptibility to liquefaction of foundation strata and scouring of the bed material should

be given due consideration. Differential settlements and sliding may also create foundationproblems.

Exclusion of heavy sediment inflow, including coarser particles, from entering and damagingthe turbines is the next important issue to be considered.

Hydrology of the river, which is highly variable from season to season and from year to year,has to be carefully analyzed for the power generation and peaking studies. In relatively largeIndian rivers, however, sufficient storage can be provided to meet the daily load fluctuations bymarginally raising the pond level for the required storage. When these power stations arelocated in plains, keeping in view the flat slopes special provisions/consideration should be

taken into account to provide the minimum required storage.

Planning and design of barrage power houses is formulated in two parts. Other part coversinvestigation, planning and layout.

For the purpose of deciding whether a particular requirement of this standard is complied with,the final value, observed or calculated expressing the result of test or analysis, shall be roundedoff in accordance with IS 2: 1960 ‘Rules for rounding off numerical values ( revised)‘. Thenumber of significant places retained in the rounded off value should be the same as that of thespecified value in this standard.



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1 SCOPE

This standard covers the hydraulic and structural design of river bed power houses integratedwith a barrage.

2 REFERENCES

2.1 The Indian Standards listed below contain provisions which through reference in this textconstitute provisions of this standard. At the time of publication, the editions indicated werevalid. All standards are subject to revision and parties to agreements based on these standardsare encouraged to investigate the possibility of applying the most recent editions of thestandards indicated below:

IS No. Title

277: 2003 Galvanized steel sheets (Plain and Corrugated)- Specification (sixthrevision)

456: 2000 Plain & reinforced concrete– Code of practice (fourth revision)

457: 1957 Code of practice for general construction of plain and reinforcedconcrete for dams and other massive structures

1786: 2008 High strength deformed steel bars and wires for concretereinforcement – Specification (fourth revision)

2062: 2011 Hot Rolled Medium and High Tensile Structural Steel – Specification(seventh revision)

4247(Part 1): 1993 Structural design of surface hydroelectric power stations: Part 1 Datafor design - Code of practice (third revision)

4247(Part 2):1992 Code of practice for structural design of surface hydroelectric powerstations: Part 2 Superstructure (second revision)

4247(Part 3):1998 Code of practice for structural design of surface hydroelectric powerstations: Part 3 Substructure (second revision)

4410 (Part 10):1988 Glossary of terms relating to river valley projects: Part 10Hydroelectric power station including water conductor system (firstrevision)

4461: 1998 Code of practice for joints in surface hydro electric power stations(second revision)

6966(Part 1): 1989 Hydraulic design of barrages and weirs -Guidelines Part 1 Alluvial

reaches (first revision)7207: 1992 Criteria for design of generator foundation for hydroelectric power

stations (first revision)

9761: 1995 Hydropower intakes - Criteria for hydraulic design (first revision)

10751: 1994 Planning and design of guide banks for alluvial rivers – Guidelines(first revision)

11130: 1984 Criteria for structural design of barrages and weirs

11388: 1995 Recommendations for design of trash racks for intakes (first revision)

12800(Part 3): 1991 Guidelines for selection of hydraulic turbines, preliminarydimensioning and layout of surface hydroelectric power houses: Part3 Small, mini and micro hydroelectric power houses

13495: 1992 Design of sediment excluders - Guidelines



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3 TERMINOLOGY

For the purpose of this standard, the following definitions should apply

3.1 Run of the River Powerhouse Integrated with Barrages

These are low-head run of the river Powerhouses located in one or some of the bays of themain barrage itself or located in a short by-pass channel or tunnel connecting the upstreampond with the downstream tail water of the Barrage.

3.2 For the other definition refer to IS 4410 (Part 10).

4 MATERIALS

4.1 Concrete

The plain and reinforced concrete should conform to IS 456. Minimum M25 grade of concreteshould be used where the structure comes in contact with water. Mass concrete shouldconform to IS 457.

4.2 Structural Steel

The structural steel should conform to IS 2062.

4.3 Reinforcement

The steel for reinforcement should conform to IS 1786.

4.4 Galvanized Corrugated Steel Sheets

Galvanized corrugated steel sheets should conform to IS 277.

5 DESIGN

The different design aspects involved are grouped into a few major sub-sections forconvenience. These are (a) Hydraulic design of the barrage, (b) Structural design of thebarrage, (c) Design of the guide bunds, (d) Design of the intake, approach channel and thetransition (e) Structural design of the powerhouse substructure, (f) Structural design of thepower house superstructure, (g) Design of the by-pass channel power house (h) Available

energy evaluation.

Design criteria for most of the above are already dealt with in several existing Indian Standardsas mentioned in clause 2. Only special provisions, wherever necessary, are mentioned below.

5.1 Hydraulic Design of the Barrage

5.1.1 For the barrages founded on alluvial rivers IS 6966 (Part 1) should be referred to.

5.1.2 For barrage in rocky bed the following modifications from IS 6966 (Part 1) arerecommended:

5.1.2.1 Retrogression



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Where the bed is composed of exposed bed rock of average strength (unconfined compressivestrength 20 MPa and above) no retrogression is to be considered downstream.

5.1.2.2 Waterway

In rocky bed (even with a shallow overburden), the permissible minimum waterway of thebarrage may be adopted on the basis of the rock strength and permissible maximum unitdischarge at high flood stage as given below:

Strength of rock in the river bed

TypeUnconfined

Compressive Strength(MPa)

Rock QualityDesignationIndex (RQD)

Permissible Max unitDischarge (m3/sec) per

meter length of waterway

Massive >100 75% 150

Jointed 50 to 100 25 to 75% 120

Highly Jointed 20 to 50 10 to 25% 80Weathered <20 10% 20

In deciding the waterway, other factors like afflux, pondage required, flushing velocity, energydissipation, flow obliquity and flow concentration, cost of protection etc. should also be dulyconsidered.

5.1.2.3 Uplift pressure

a) In weathered and highly jointed bed rock, uplift pressure is to be calculated by anyaccepted practice.

b) If the bed rock is reasonably impermeable (coefficient of permeability variation 5x10-4

to1x10-7 cm/sec) but moderately jointed and the major joints are more or less parallel tothe river flow direction, two rows of curtain grout (cement or chemical) may be injectedabout 3 to 5m downstream from the upstream end of the pucca floor, for a depth equalto the maximum pondage head. The uplift pressure may be assumed as 50% of the fullhead at the grout curtain line, reducing to in the minimum tail water level at thedownstream end. As an additional measure pressure relief pipes can be provided underthe stilling basin.

c) If the bed rock is reasonably impermeable (coefficient of permeability variation 5x10-4 to1x10-7 cm/sec) but moderately jointed and the major joints are perpendicular or nearlyperpendicular to the river flow direction, the uplift pressure may be assumed as 25% full

head on the upstream end reducing to the minimum tail water level on the downstream.

d) If the barrage is on dense rocky bed (coefficient of permeability variation, below 1x10-7 cm/sec and above), the uplift pressure may be assumed as varying from 15% of fullhead on the upstream end to minimum tail water depth on the downstream end.

5.1.2.4 Energy dissipation

In order to avoid erosion and other problems energy dissipation arrangement should beadequate to ensure that undesirable residual kinetic energy of flow does not pass downstreamof barrage. If the river bed rock downstream of the stilling basin is relatively dense (specificationstrength and RQD), it is not necessary to provide the maximum length of stilling basin requiredfor full hydraulic jump under maximum pond condition. The basin length required for the jumpunder minimum 2 m gate opening is considered sufficient. For lesser openings, the residualenergy from the incomplete jump will not be harmful to a relatively dense rocky bed (unconfined



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comp. strength > 50 MPa and RQD > 50%). Hydraulic jump being unstable in the range ofprejump Froud’s number of flow (F1) varying from 2.5 to 4.5, efforts should be made to avoidthis range by suitably adjusting waterway and pond/afflux. If it is not feasible to avoid,appropriate stilling basin (as per relevant Indian Standard) should be adopted.

5.1.2.5 Sediment Excluder

In rocky bed, generally sediment excluders are not needed, unless the bed is mobile and thereis sandy or pebbly bed load movement over the parent bed rock.

Exclusion of mobile gravels and boulders from power bay is essential to prevent damage toturbines. Maximum site of sediments which can be allowed to move through power bay will begoverned by head and type of materials.

5.1.2.6 Scour

In rocky bed of average strength & RQD and moderate joints, Lacey’s scour formula does notapply. A nominal depth of cut-off of 2.5 m under the downstream end of the pucca floor isrecommended. No downstream flexible protection is necessary.

If the bed rock is highly jointed or weathered, some scour may take place and lacey's scourformula may be adopted, assuming the bed rock ultimately disintegrating to a mixture of graveland coarse sand (approximately 5 mm dia.) condition. The scour in alluvial reaches particularlybouldery should be worked out by using Thomson & Gambell formula. The depth of cut-offs tolimit exit gradient of sub-surface flow should be governed by existing analytical methods as alsoelectrical analogy, and flow nets etc.

5.2 Structural Design of Barrages

5.2.1 The provisions covered in IS 11130 should be referred to.

5.2.2 Where movement of boulders and gravels may occur over the barrage bays, special

protective measures like granite blocks, etc. over the concrete surface should be used alongwith high performance and special concrete with polymers for protection against abrasion andimpact.

5.3 Design of Guide Bunds

5.3.1 The provisions covered in IS 10751 should be referred to.

5.3.2 On the river bank adjacent to the proposed powerhouse, the guide bund should be

carefully curved from a long distance, so that no oblique flow develops in the approach channelof the powerhouse. The upstream abutment should be continued with vertical face for adistance equal to the length of the first block of the in-stream powerhouse. Thereafter, the wallcan be gradually sloped to merge with that of the upstream guide bund. To avoid cross-flowand eddy, a divide wall may be used to separate the power bays from the weir bays by theguide bund and divide walls may be finalized for hydraulic model studies.

5.4 Design of the Intake Structure and the Approach Channel

5.4.1 The main components of an intake structure for the low head run-of-the-river powerhouseare:



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a) Intake flume with transition from rectangular to circular opening at the entry and adiffuser at the exit to minimize head losses

b) Trash rack and supporting structure

c) Sediment flushing device and some trapping arrangement for boulders at upstream

locationd) Anti- vortex device if necessary

e) Stop-log and head gate slot enclosures

5.4.2 In cases where there is a considerable movement of boulders, stones and sand in the

downstream direction, the intake should be so arranged that the effect of such movement willnot lead to a partial restriction or blockage of the intake. Hydraulic model studies may benecessary under special conditions.

5.4.3 Intake flume

a) The length of the intake flume is determined by the requirements of space for theinstallations within the passage, and should have sufficient space to accommodate,trash rack, stop-log, head gates, necessary transition lengths etc.

b) To prevent vortex formation, the central line of the intake flume should be located belowthe minimum draw-down level such that the minimum cushion of water over the roof ofthe flume at the entrance is 0.3 h e , where h e is the entrance height of the flume (Fig 1).

c) In case of oblique flow, this water cushion may be raised upto h e .

d) The requirement of water cushion may be reduced with the provision of anti-vortexdevices.

e) The flume can sometimes be inclined, depending on the need of sediment or boulderexclusion devices such as shingle flushing channel/ conduit, sediment excluder etc. onthe upstream (See fig. 1).

f) The normal contraction of 30 percent should be used for low-head installations toensure uniform flow through turbines.

g) In the diffuser transition, the side walls should not expand at a rate greater than anangle of 50 with the axis of the main flow.

h) All slots for gates and stop logs should normally be outside the transition zone.

5.4.4 Trash racks

a) For low-head powerhouses, a straight trash rack is usually preferred, slightly inclined(700 to 800 with the horizontal) for easy raking. IS 11388 should be referred for thedesign of trash racks.

b) Sometimes, a skimmer wall is also provided, submerging to a depth of 0.5 to 1.0 mbelow minimum drawdown level, to retain material floating on the water surface.

c) In the Power houses located in by-pass channels, the skimmer wall is not necessary.

d) The normal velocity of flow through the racks structure is indicated below:

For units with hand raking v = 0.75 m/secFor units with mechanical raking v= 1.5 m/sec

e) Trash rack bars should be so spaced that the clear spacing between bars should be atleast 5 mm less than the minimum opening between turbine runner blades as per IS9761.



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f) To prevent entry of logs/trash in to the intakes provision of log booms at an upstreamlocation should be considered.

5.4.5 Sediment flushing

a) For flushing the sediments, boulders, etc, a sediment trap near to entrance sill (low

baffle wall in the river bed) of 0.5 m to 3.0 m height may be provided on the upstream ofthe intake, to divert this rolling bed material to the adjacent barrage bays. Sedimentflushing conduits (See fig. 2) are also sometimes necessary.

b) It is not necessary to remove suspended sediments as these do not normally cause anydamage to the turbines running under low head.

5.4.6 Special provisions

a) Anti vortex devices like floating timber frames or perforated breast wall may help inreducing the minimum water cushion necessary for preventing the vortex formation.

b) Wherever the intakes are situated at high altitude above snow line, de-icingarrangements like bubbler system or heating arrangements may be provided forarresting ice-formation on rack bars and gates.

c) Stop log provisions should be kept both on the upstream and downstream of themachines.

d) The approach apron should not be placed closer than 30 percent of the intake height(h e ) from the lower edge of the intake orifice as per IS 9761. The upward slope of theapron can be 1:1 or flatter.

e) The up-slope of the exit channel should not be steeper than 6(H):1(V). Adequate bedprotection, preferably of concrete may be provided for the full length of the slopingapron.

5.5 Structural Design of Powerhouse Substructure

5.5.1 The stability analysis of power house as well as barrage structure should be carried outprior to processing the structural analysis. Detailed investigation of the engineering propertiesof the foundation material should be carried out by suitable field tests as per relevant IndianStandards. The main design concepts of the sub-structure of low-head river bed powerhousesbeing basically the same as those of a surface hydro power station, the criteria stipulated in IS4247 (Part 3) should be followed.

For the design of the generator foundation for machines with vertical axis, IS 7207 should be

referred.

5.5.2 Some special features mentioned below are to be taken care of, when the river-bedpowerhouse is designed in continuation of a barrage structure.

5.5.2.1 Structural stress analysis

a) When the powerhouse is to be constructed on soft river bed composed of boulders,sand or sandy silt, its substructure should be designed by analytical/numerical method.Either (i) as an elastic raft foundation,or (ii) as a rigid frame on uniform soil reaction,

or (iii) as a rigid box structure resting on caissons or wells.Pile foundations should be avoided.



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b) Depending on the thickness and rigidity of the concrete mass up to the machine hallfloor level (considering all the openings) and the relative elasticity of the naturalfoundation media, the design can beEither (i) as an elastic structure on elastic foundationor (ii) as a rigid structure upon elastic foundation (See Fig. 3)

c) In bouldery bed, the base being relatively more steady, the powerhouse blocks can bedivided by vertical joints into groups. The foundation pressure can be assumed asuniform. The analysis of each block can be done as a plane frame (See Fig. 4).

d) In rocky bed, the load from the superstructure may be assumed to go down directly tothe bed through the Piers. The bottom slab can be separated from the Piers and sidewalls, but suitably anchored below and provided with temperature reinforcements.

e) Where the foundation grade is silty sand, silt or plastic clay, evenly distributed groundpressure are desirable. This may be achieved by suitably modifying the position of theinternal openings or applying extra cavities etc.

f) The Foundation concrete mass should also be checked for vibration effects to eliminatethe possibility of any resonance.

5.5.2.2 Settlement

Relative settlement between the two ends of a powerhouse block is of vital importance. Inhydropower structures the limit of unequal settlement should not be more than 0.0003 L whereL is the distance between the points settling unequally. This should however be governed byserviceability requirement of the structure.

To reduce differential settlement, consolidation grouting of the foundation and enclosing thefoundation periphery by sheet piles may be useful. Where the foundation strata is weak and

heterogeneous in nature use of compacted soil matrix below the foundation raft can also beconsidered based on the analogy of concrete faced rock fill dams.

5.5.2.3 Sliding

The criteria mentioned in IS 4247(Part 3) should to be adhered to.

5.5.2.4 Floatation

The criteria mentioned in IS 4247 (Part 3) should be followed.

It may be useful to drive a row of sheet piles or cut-off all around power house foundation toreduce uplift pressure below the upstream end of the powerhouse raft. The measures againstsub-surface flow/scour, finalized for the barrage should also be extended beneath the powerhouse structure. In general as the thickness of power house raft is quite large and is alsosubjected to heavy machine loads, it is safe from uplift considerations.

It may also be useful to provide on the upstream approach channel bed, for some distance, athin concrete layer covered with compact clay. The top of this clay layer is to be protected byprecast cement concrete blocks, with a thin intervening layer of graded filter.

5.5.3 Approach and exit velocities

The flow velocity in the approach channel of the powerhouse may be restricted as follows:



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H (Generating head) m 2 4 6 8 10 15

V (Approach velocity) m/sec 1.0 1.1 1.3 1.5 1.7 2.1

At the exit end, the outflow channel may be carefully protected from scour for a considerable

distance, to prevent the formation of cavities under the tail pool bed slab.

In soft foundation, end sheet piles or concrete cut-off walls should be used. Suitable protectivepaving, preferably with cement concrete, should be provided in the bed and sides on thedownstream. In the soft foundation strata, confinement of structural independent units bymeans of shallow cut-offs all around may be considered to impart additional stability.

Properly designed divide walls of adequate length should separate the approach and exitchannels of the powerhouse from the adjacent barrage bays.

5.5.4 Expansion and contraction joints

The provisions given in IS 4461 should be referred. When the power house is in conjunction ofexisting barrage the joining pattern of the barrage should be followed.

5.6 Structural Design of Powerhouse Superstructure

5.6.1 The main design concepts of the superstructure of a low head river bed powerhousebeing basically the same as those of a surface hydro power station, the criteria and guidelinesstipulated in IS 4247 (Part 2) should be followed.

5.6.2 IS 12800 (Part 3) should be referred for dimensioning and layout of small, mini and micropowerhouses.

5.6.3 Some additional features mentioned below are required to be considered while designingthe in-stream powerhouses integrated with a barrage.

5.6.3.1 Continuation of the road bridge over the power house

The in-stream powerhouse being in continuity of the main barrage structure, the road bridgeover the barrage has to cross over the power house. This bridge is most conveniently locatedover the draft tube. The draft tube structure should therefore be designed considering the roadbridge load over it (See Fig. 1)

5.6.3.2 Crossing of the barrage gate gantry crane

Vertical lift gates are generally provided in the barrage bays, which need high trestles andmobile gantry crane for operation and maintenance. These cranes generally requireapproaches from both the river banks. Therefore, it has to travel over the in stream powerhouse also. In outdoor and semi-outdoor type power house, this crane can be combined withthe power house gantry.

5.6.3.3 Submersible type power house

In narrow gorges, where the in-stream power houses occupy considerable waterway, the

spilling capacity of the barrage can be increased by allowing part of the flood to pass over thepower house. The down-stream river bed has to be properly protected against scour. Sidechannel, chute or shaft type spillways may also be considered to augur spillway capacity.



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5.7 Design of By-pass Channel Power House

5.7.1 The design criteria of the by-pass channel power houses are practically the same as

those of the river-bed power houses and most of the guidelines mentioned above are

applicable.

5.7.2 It is desirable to locate the power house near the tail end of the by-pass channel, foreconomy in the cost of excavation.

5.7.3 A head regulator is necessary at the entry point of the channel, provided with suitabletrash rack arrangement.

5.7.4 If desilting is considered necessary, sediment ejector may be provided as per provisions

contained in IS 13495.

Note: Normally, in low head power houses exclusion of suspended sediment is not required, as it doesnot harm the turbine blades under low head.

5.8 Available Energy Evaluation

5.8.1 Daily or ten-daily average discharges available in the river at the proposed power house

site throughout the year has to be collected for as many years as possible. At least 10 yearsreliable data should be collected.

5.8.2 From the above data, the discharge figures for an average year are to be selected and

arranged in descending order. With these data, frequency of occurrence (on percentage ofduration) is found. For any given discharge or above it, the discharge (Q) and Percentage -

Duration curve is plotted (see Fig. 5).

5.8.3 On the same graph, the average tail water stage - duration curve (tail water level

corresponding to a given discharge is obtained from the stage-discharge curve) is plotted.

5.8.4 The pond level for the barrage is decided from practical considerations like, peaking

required firm power discharge available, submergence, cost of embankments, shoal formationetc. (refer 5.10).

5.8.5 The effective pond level is obtained after deducting the total head losses due to

contraction, trash, entrance, rack, gates, stop log, expansion and exit velocity head) from the

pond level (see Fig. 5).

5.8.6 Deducting the top water level (T.W.L.) from the effective pond level, the net availablehead (H) is found and losses due to friction in the system corresponding net head-durationcurve is then plotted (Fig 5).

5.8.7 On the net head duration curve, a rated head (HD and the corresponding rated design

discharge Q for the turbine, quite close to the maximum available power (Pmax) (see Fig 5 andclause 5.8.8 ) has to be decided. The turbine and the generator are then to be selected, to givemaximum efficiency for these parameters (that is, rated head and rated discharge).

5.8.8 From the above plots of Q & H and by using the formula P = 9.81 η QH (kw), the Power(P) duration curve is plotted (Fig 5). Overall efficiency (η o) is the product of the efficiencies of

the turbine (of η T), generator (of η G) and transformer (of η Tr) i.e. η o =η T.η G.η Tr



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The maximum power output Pmax will be equal to 9.8η o Qr Hr where Qr and Hr are the rated

discharge in cumec and rated head in metre respectively. Pmax is the plant power capacity.

5.8.9 From the power- duration curve, the total energy that can be generated in an average

year is then calculated as E =∑ ∫ pdt .

5.8.10 In the absence of the actual efficiency coefficients for the machines and the losses, the

following figures may be assumed for the preliminary assessment of the available energy:

Rack loss = 5 to 20 cm approx.

Entrance loss = nil

Exit velocity head = 5 to 10 cm approx.

Turbine efficiency = 0.85 to 0.92

Generator efficiency = 0.92 to 0.97

Transformer efficiency = 0.94 to 0.98

5.9 Fixation of the Pond Level / Afflux

5.9.1 In a relatively plain topography, the pond level/afflux of the barrage cannot be fixed muchhigher for following reasons:

a) Extensive submergence of land upstream due to backwater effect,

b) Costly marginal/afflux embankments to train the river and flood protection,

c) Shoal formation in the pond due to slack flow in the backwater reach, and

d) Insufficient approach velocity needed for flushing of sediments deposited in the pond.

However, the effect of a low pond level is that, no power can be generated during the floodperiod, because the net head (H) will tend to be zero (Fig. 5).

In deciding the design pond level an economic balance has to be struck, considering therevenue earned from energy on one hand and the cost to raise marginal bunds and occasionalstagnation of the low-lying areas in the country side depressions on the other side. The localtemporary water logging can be cleared either by pumping or by a parallel drain dischargingdownstream of the barrage. For creating enough flushing velocity height of masonry part of thebarrage should be limited and ponding should be achieved by constructing high head gates.

5.9.2 In the hilly regions, however there is not much problem of sub-mergence or marginalembankments, even if the pond level is kept considerably high than the high flood level. But thepond must be periodically flushed by regulating gates so that the requisite drawdown of thepond can be achieved.

Storage being of little importance in the run-of the river power station accumulation of bouldersin the pond and shoal formation may be permitted. Sediments so deposited may bemechanically removed by shovels and dozers, once a year and also by periodic flushing ofpond by gate regulation during monsoon.

5.10 Peaking

If the backwater of the pond extends for a considerable distance upstream, a little extra head ofin the pond will help in creating considerable storage of water which will allow peaking



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operation during the peak hours, by storing for several hours and then releasing the storedvolume during the peak demand hours, depending on the typical load-demand curve of theregion.



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