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vikram.jeet
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PostPosted: Fri Jun 11, 2021 8:11 am    Post subject: Reply with quote

DAM / BARRAGE CONSTRUCTION - RIVER DIVERSION WORKS

Construction of Headworks across the flowing river can not be started unless stream is diverted from area of working in the river bed itself. The Diversion scheme is to be planned at the outset  . River Diversion can be achieved  based on :

Availability of space to pass the flood discharge
In case river is wider and half of width is sufficient to pass floods , the easiest way is to do construction in one half and a longitudinal bund of 6 to 8 m is constructed running from u/s to down stream , completely sealing the working area for half construction of head work. This  generally happens in upper reaches/high altitudes where schemes of low discharge high head are planned. The Diversion is done to pass flood discharge .
(To be controlled)
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vikram.jeet
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PostPosted: Fri Jun 11, 2021 2:27 pm    Post subject: Reply with quote

RIVER DIVERSION - DIVERSION TUNNEL

In case of narrow gourge site at Headworks construction , the only option left is DIVERSION TUNNEL nick named as DT. It is a bypass  tunnel , bypassing the Headworkss construction area.lt is planned for maximum NON MONSOON FLOOD. This Tunnel takes a loop curve in the mountain and water from upstream is passed on to this tunnel by constructing an upstream COFFERDAMS .  Tunnel on down stream discharge into river . A DOWNSTREAM COFFERDAM is constructed to prevent water entering the construction area.

During Monsoon months all plant and machinery is removed from site  and   COFFERDAMS are allowed to overtop by flash floods
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vikram.jeet
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PostPosted: Sat Jun 12, 2021 4:34 am    Post subject: Reply with quote

RIVER DIVERSION - DIVERSION CHANNEL

Sometimes river Diversion is effected by constructing Diversion Channel . Hydro projects at foothills require Dams of low height and diversion of non monsoon floods are to be diverted in open channel on one bank . Channel can be of gravity  bund  with clay core if space permits  but sometimes RCC base slab with retaining walls is provided.
Once dam construction is done upto certain level , water is passed through under sluices openings and flow in channel is stopped for  remaining construction on this side.

However everything depends on topography at river banks.
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vikram.jeet
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PostPosted: Sat Jun 12, 2021 6:49 am    Post subject: Reply with quote

HEADWORKS  - DESIGN  FLOOD

Dams  are generally designed on Flood discharge of One in Thousand years return period flood  which can be The Probable Maximum Flood (PMF ).

The Downstream stilling works , upstream works are generally designed for lower return period of 1 in 200 yrs flood.

Diversion works are designed for 1 in 20 Years Non monsoon Flood Discharge.
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PostPosted: Sat Jun 12, 2021 2:24 pm    Post subject: Reply with quote

HYDROPOWER

THE POWER GENERATED IN MEGAWATTS

P = 9.81*10^-3 * Q *H(net) * Turbine efficiency* Generator efficiency

Q is the discharge in cumecs
H(net) is net head  = FRL(Headwork)  - turbine centerline level  - Loses in water conductor system in  case of  Impulse turbines e.g. Proton
H(net) is net head = FRL (head work)  - D/s water level at turbine  - Losses in water Conductor system      in case of Reaction turbine e.g.Francis

Turbine efficiency & Generator efficiency is based on manufacturers
Specifications /Certificate.
Generally turbine efficiency is in range 93 to 95%
Generator efficiency is around 95 to 98%

Machine availability for working out annual power  is generally 95%.
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PostPosted: Sat Jun 12, 2021 2:54 pm    Post subject: Reply with quote

GAUGE - DISCHARGE DATA

This data is generally maintained by State Irrigation and Power Department s / NHPC. / Central Water Commission. G-D stations are installed at designated locations of rivers. For given location  of Dam/  Barrage  the nearest two stations data , on u/s and other one on d/s are taken into consideration and modified for location of Headwork. Also the Constuction Agency , on award of work, start measurements at the exact location .

The G-D data is required at following locations of river:-

Dam / Barrage site
Tail Race outfall site
Silt Flushing Duct outfall site
Main Access Tunnel site

This data of discharge Vs river water level is used for detailed planning and design.
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PostPosted: Sun Jun 13, 2021 5:23 am    Post subject: Reply with quote

RESERVOIR CAPACITY - UPSTREAM OF DAM

This is important to work out water available on storage u/s of Dam
River crossection are taken at 50 m interval on upstream.
The Full Reservoir Level (FRL) is the maximum level , beyond which it is to be allowed to pass on.
Maximum Drawdown Level  (MDDL) is the level upto which water needs to be drawn.

Based on X sec data , reservoir areas at 1m ht intervals are worked out and AREA - ELEVATION CURVE needs to be drawn.

Accordingly based on Area - Elevation curve, The CAPACITY - ELEVATION curve is developed.

These are used used by Hydrologists for planning / design of Headworks,
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PostPosted: Sun Jun 13, 2021 6:29 am    Post subject: Reply with quote

RIVER DISCHARGE DATA AT DAM SITE

River , during non monsoon periods, flows with varied flows bringing water from catchment area on upstream . The water from glaciers at high Altitudes is a continuous source  , but it depends on melting of glaciers and Hourly variations are expected in a day. Also seasonal variation depending on summer /winter months.
The precipitations in hills and upper reaches also add to water flow.

This data of hourly , daily mean, 10 daily mean  are all required for working out the available water Discharge for design .
Also , Monthly Peak flow , Annual Peak flow are all required to analyse and calculations of  Maximum Flood discharge at various return periods , for dam it is 1 in 1000 years.
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vikram.jeet
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PostPosted: Sun Jun 13, 2021 7:23 am    Post subject: Reply with quote

MAXIMUM FLOOD DISCHARGE FOR DESIGN

DAMS are structures of highest importance . Large quantum of waters are stored and the  upstream and downstream areas are are affected highly as result of ponding of water / As also during its release during monsoon floods.

Estimation of PROBABLE MAXIMUM FLOOD (PMF) is all the more important for safety of Dam structure as well as population living in nearby hilly areas

Basic data , as already said in previous post, is the Annual Peak Discharge records of last 20 to 30 years or even more , if available.
Various empirical and Statistical Methods are used to analyse this data and based results of all these methods , Flood Discharge Vs Return period relation of particular Catchment at specified Dam site location is developed.
(to be controlled.)
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PostPosted: Sun Jun 13, 2021 2:34 pm    Post subject: Reply with quote


FLOOD DISCHARGE ESTIMATION

(In continuation)


Various Statistical Methods used to access the Flood discharge are :


GUMBEL'S METHOD OF FLOOD FREQUENCY ANALYSIS
LOG NORMAL METHOD
LOG PEARSON METHOD




Also some  Empirical Methods are also used , namely:


DICKEN'S FORMULA
RYVE'S FORMULA
INGLIS FORMULA
NAWAB JUNG BAHADUR FORMULA
W.P.CREAGER'S FORMULA
JARVIS FORMULA
MODIFIED MYER'S FORMULA
BURGE FORMULA
PETTIS FORMULA
BOSTON SOCIETY OF CIVIL ENGINEERS FORMULA


Discharge estimation from Hydrograph
UNIT HYDROGRAPH  METHOD
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