TEHRI DAM & RESERVOIR

River Discharge: 30 to 7500 Cumec Design Flood: 15,540 Cumec Gross Storage: 3,540 MCM Live Storage: 2,615 MCM Mean Annual Run-off: 8,000 MCM Catchment Area : 7,299 sq km Snowbound: 2,424 sq km Rainfed : 4,863 sq km Annual rainfall: 1,016 to 2,630 mm Max. Flood Level : EL 835 m Full Reservoir Level : EL 830 m MDDL : EL 740 m

Tehri Power House (1,000 MW)

KOTESHWAR RESERVOIR (Located 22km downstream of Tehri Reservoir)

Downstream view of Koteshwar Dam

KOTESHWAR RESERVOIR (Located 22km downstream of Tehri Reservoir) Gross Storage: 88.9 MCM Live Storage: 35 MCM Mean Annual Run-off: 8,000 MCM Catchment Area : 7,691 sq. km at dam site Snowbound: 2,328 sq. km Annual normal water flow: cumecs Max. Flood Level : EL 615 m Full Reservoir Level : EL m MDDL : EL m

TEHRI AND KOTESHWAR RESERVOIR FRL. EL M MDDL. EL M FRL. EL M MIN.LEVEL EL. 606 M TEHRI DAM ( STAGE-I) KOTESHWAR DAM ~ 22 KM TEHRI RESERVOIR KOTESHWAR RESERVOIR

ROLE OF TEHRI RESERVOIR Tehri HPC was conceived & designed to store surplus water of the river Bhagirathi during monsoon and releasing the same during the lean season as per the requirement of command area for drinking and irrigation purposes and to provide peaking support to grid by Tehri HPP & PSP. ROLE OF KOTESHWAR RESERVOIR The Koteshwar project is an integral part of Tehri HPC. The Koteshwar reservoir is to serve the purpose of re- regulation of the flow released from the Tehri reservoir, in order to maintain uniform continuous flow d/s of Koteshwar. TEHRI RESERVOIR OPERATION

 The hydrology year in the Central Himalaya starts from 21st June. Around this time the reservoir level is brought to its minimum level at EL i.e. MDDL (Minimum draw down level below which no power generation can takes place) so that complete storage capacity remains available to store surplus water of monsoon.  From 21st June to 31st October (monsoon period) water is allowed to fill in the reservoir.  From 1st November to 20th June, stored water including the natural inflow is allowed to be released as per UPID requirement thus touching MDDL (EL 740m) around 20th June. TEHRI RESERVOIR OPERATION

Reservoir Operation DURING MONSOON  Average Inflow & Outflow during monsoon are as below Sl.No.Year Average InflowsAverage Outflow CumecsMCMCumecsMCM TEHRI RESERVOIR OPERATION

Reservoir Operation DURING NON-MONSOON  During lean months (1st Nov to 20th June), in addition to natural river inflow, water stored in the dam is also released.  The annual schedule for release of water from 1st Nov to 20th June is prepared in mutual agreement with UPID.  Live storage corresponding FRL i.e EL 830 is 2615 MCM, which will allow average release around 130cumecs (4550cusecs) apart from releasing the natural inflow. In lean period. TEHRI RESERVOIR OPERATION

Reservoir Operation DURING NON-MONSOON  During the lean months when river Bhagirathi inflow varies from 40 to 80 cumecs, it is augmented to make it 180 to 250 cumecs by releasing water from Tehri dam reservoir.  Water released from Tehri dam not only revive river Bhagirathi but river Ganga also because overall flow of river Ganga also decreases considerably during the months of Dec, Jan & Feb. Availability of water in the river decreases to an extent, if not supported by Tehri dam reservoir, would covert into a nala in the farther plain areas. TEHRI RESERVOIR OPERATION

Reservoir Operation DURING NON MONSOON  Average Inflow & Outflow during non-monsoon are as below Sl.No.Year Average InflowAverage Outflow CumecsMCMCumecsMCM TEHRI RESERVOIR OPERATION

Average Monthly Flow Ratio Month River Ganga at Rishikesh 36 years ( ) Pre Tehri flow (Cumec) 7 years ( ) Post Tehri flow (Cumec) Post to Pre Tehri flow Ratio June July Aug Sep Oct Nov Dec Jan Feb March April May

Reservoir Operation DURING NON-MONSOON TEHRI RESERVOIR OPERATION  The average flows during the lean period has been augmented during all the lean months (Nov- Apr) which reflects the special characteristics of storage type reservoir. It is worth mentioning that the minimum flow of Ganga river have been augmented by 1.2 times to 1.8 times at Rishikesh.  The typical lean period (Nov-Apr) flow augmentation shows the way how this type of reservoir may increase the river flow during lean months of a year.

 The water levels in Tehri dam were low at the start of the monsoon. This proved a critical factor in the dam retaining waters of an engorged Bhagirathi and preventing a feet rise in the Ganga at Rishikesh that could have been ruinous for the town and its ashrams.  Without Tehri dam, Rishkesh, Haridwar and parts of western UP would have been inundated.  At Devprayag, the confluence of Bhagirathi and Alaknanda, the river level was m at 11 am on June 16, the next day around the same time, the rise in water level was by 11 meters to m. “It would have been a catastrophe downstream of Devprayag, in Rishikesh and Haridwar, if instead of 14,000 cusecs, 2,44,000 cusecs was added from Bhagirathi” ROLE OF TEHRI DAM DURING FLOOD OF 2013

ADDITIONAL WATER FOR GANGA SNANS  Tehri reservoir provides additional water for Snans during Kumbh Mela, Magh Mela etc.  Tehri reservoir played important role in Kumbh Mela 2010 &  During Kumb Mela 2010 & 2013 Tehri reservoir released Cumecs against the inflow of Cumecs during Snan Days.Kumb Mela 2010 & 2013  Every year additional water is released from Tehri dam for Magh Mela in Jan & Feb. TEHRI RESERVOIR OPERATION

Kumbh Snan