Tehri Dam Catchment and Flood Management Case Study.pptx

Its very important topic

1. Catchment Treatment and Rehabilitation for Management of Riverine Flo ods … A case of Tehri Dam 1

2. R ese r v oi r s mos t i mporta n t …. w a t er r esou r c es development and management – To regulate -flow modify temporal and spatial availability of water through out year. To s t o r e f l oo d w a t er , m o de r a t e f l o od - p eaks and save d /s areas from damages. S tored monsoon water used for irrigation, domestic and industrial needs along with hydro power generation etc. To p r o v id e water p o ol f or n a viga t i o n , habitat f or aqu a ti c li ves , facilities for recreation and sports. Other multipurposes Etc. etc 2

3. Rehabilitating rivers and floodplains, and treating catchment areas play a significant role in flood control by Restoring and increasing a river's capacity to flow and reducing the speed of water flow. Catchment area treatment (CAT) plans to improve the environmental conditions of a region by understanding and reducing the rate of erosion in the terrain. River and floodplain rehabilitation To increase protection from floods caused by heavy precipitation, storm surges, and rising sea levels. To help preserve habitats, improve biodiversity, and maintain aquatic ecosystems. Catchment area treatment reduce soil erosion and water runoff, which help build a sustainable water supply. CAT plans rejuvenate ecosystems in the catchment area to prolong reservoir storage capacity. Catchment area of a flood is a hydrological unit. Each drop of precipitation that falls into a catchment area eventually ends up in the same river going to the sea from there if it doesn't evaporate. However, it can take a very long time. Catchment areas are separated from each other by watersheds. Natural flood management When used with other flood management solutions, it can reduce flood risks downstream. It can improve water quality and biodiversity, and make catchments more resilient to climate change.

4. Land use changes Sustainable soil management practices and changes in land use help with carbon sequestration and storage. Reducing large areas of land uses like wet paddy fields and ponds increase the amount of rainwater available for flooding downstream. Other flood control techniques include: Installing rock berms and rip-raps, Using sandbags, Maintaining slopes with vegetation, Applying soil cements to steeper slopes, and Constructing or expanding drainage channels. Structural flood control and Other Activities of Flood Control River rehabilitation and restoration help with flood control by restoring the natural functions of rivers that have been degraded by human interventions.   Increasing river capacity: by increasing the velocity of the river's water flow, which reduces the river's stage and increases its capacity.   Diverting Water from a main river into other channels, called floodways.   Straightening river channels: To speed up water flow giving less time it for collecting in areas that are prone to flooding.   Deepening river channels: to carry more water.   Preserving natural floodplains: to dissipate without causing extensive damage.  Incorporating green infrastructure: This includes wetlands, vegetated swales, rain gardens, green roofs, and swales. 

5. In g eneral five basic zones of reservoir space used in operating a reservoir for various functions. S torage allocations for various uses :

6. Tehri Dam to store surplus water of river Bhagirathi (and Bhilangana) tributary of river Ganga, during monsoon releasing stored water after monsoon on irrigation needs of UP drinking water for Delhi and UP peaking power to Northern grid operational since 2007. 6

7. H ari dw ar 7

8. Type Height of dam Base Width at top Length at the top : R ock and Earth f ill : 260.5 m : 1128 m : 25.5 m : 575 m 8

9. SH E L L SH E L L R IP - R AP FINE FIL TER MAIN DAM AXIS EL. 839.5 M U /S D/S COFFER DAM R IP - R AP FSL 830.0 M C O ARSE FILTER EL. 632.0 M INSPECTION GA L L ERY (EL. 725 M) CO R E IN SP E C TI O N GALLERY (EL. 835 M) : 201.6 LAC CUM : 35.3 LAC CUM : 15.10 LAC CUM : 27.8 LAC CUM SHELL CLAY FI L TE RS R IP RAP TOTAL QTY OF FILL PLACEMENT: 279.8 LAC CUM 9

10. Water Spread Gross Storage Live Storage Max. Flood Level Full Reservoir Level MDDL : 42 SQ KM : 3540 Million Cum : 2615 Million Cum : EL 835 m : EL 830 m : EL 740 m 10

11. DIFFERENT OPERATIN ZONES OF TEHRI RESERVOIR Dead Storage Zone – Below EL 700m i.e. lowest outlet (ILO) level Buffer Zone – From EL 700m up to 740m (MDDL) Conservation Zone – From EL 740m (MDDL) up to 815m (Spillway Crest Level) Flood Control Zone – From EL 815m (Spillway Crest Level) up to 830m (FRL) Spillage Zone – From EL 830m (FRL) up to 835m (MWL) El 700m El 740m El 815mn El 830m EL 835m

12. Spillway System 12 Spillway system of Tehri to cater 1 in 10000 years return period flood peak discharge of 15540 cumecs and consists of – Gated Chute Spillway with crest at EL 815m Gated Left Bank Shaft Spillway (LBSS) with crest at EL 815m Un-gated Right Bank Shaft Spillway (RBSS) with crest at EL 830.20m Chute spillway and LBSS regular spillways whereas RBSS emergency spillway which comes into operation automatically when water level crosses WL 830.2m

13. CHUTE SPILLWAY Head : 220 M Type : Conventional Stilling Basin type Max Discharge : 5500 cumecs Width : 39.5m at top and 50m at toe Regulating Gates : Radial 15.5m high/10.5m wide Aerators : 3 nos on Glacis Stilling Basin : 140 x 50 m, 22m deep pool 55 m high walls D/s River Bed : Protection by Concrete Blocks 13

14. LEFT BANK SHAFT SPILLWAYS Head : 220 M Type : Vertical Shafts Nos : 2 (Gated) Intakes : Tunnel type (80m long) Total Discharge : 3800 cumecs Vertical Shaft : 12m dia J u n ct i on with : Tangential with 5.5m tunnel opening De-aeration : Th r o u g h a S epa r ati o n Cha mber and S y s t em de -ae r ati o n shaft opening in a De-aeration tunnel V eloc i ty at t oe : 45 m/s 14

15. RIGHT BANK SHAFT SPILLWAYS Head : 220 M Type : Vertical Shafts Nos. : 2 (Un-gated) Intakes : Funnel type (34m dia) Total Discharge : 3900 cumecs Vertical Shaft : 12m dia. Junction with : Tangential with 6.0m tunnel opening De-aeration : Th r o u g h a S epa r ati o n S y s t em Cha mber and de-aeration shaft opening above MWL V eloc i ty at t oe : 45 m/s 15

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17. Power House Cavern Size T yp e of T u r bines Rated Head Speed Installed Capacity Annual Design Energy Transmission System U nde r g r o u nd 1 9 7 mX24 m X 6 3m F r ancis 188 M 214.3 RPM 4X250 MW 2797 MUs 400 KV 17

18. A Major Flood Mitigation 18

19. Catchment : supports water stream in varying shape of channel, with loads of minerals etc has ability to support life healthy as its surrounding catchment. Catchment a basin shaped area of land, bounded by natural features such as hills or mountains from which surface and sub surface water flows into streams, rivers and wetlands. Water flows into, and collects in, the lowest areas in the landscape. The system of streams which transport water, sediment and other material from a catchment are drainage network. A catchment catches water which falls to earth as precipitation (rainfall), and the drainage network channels the water from throughout the catchment to a common outlet. The outlet of a catchment is the mouth of the main stream or river. The mouth may be where it flows into another river or stream, or the place where it empties into a lake, estuary, wetland or ocean. Catchments of tributaries are referred to as sub-catchments. Whatever happens in each of the smaller streams affects the overall wellbeing of the main waterway. No catchment is exactly like another. Each has a different size, shape, drainage pattern and features that are determined by natural processes, particularly geology and climate. Weathered rock and organic matter make up the soils that blanket the landscape. Soils have different textures, mineral content, structure and drainage properties. The nature of the soils in your catchment will have a key role in deciding how much water runs off the land and how likely the land is to erode.

20. Tehri Dam's catchment area  7,288 square KM, with 2,042 square KM of permanent snow=cover.  Tehri Dam catchment is located between 78°9'15''E to 79°24'55''E longitude and 30°20'20''N to 31°27'30‘’N latitude.  Elevation of the catchment ranges from 600 meters at the dam site to 7,000 meters at the Gangotri glacier peak.  Catchment receives most of its rainfall during the southwest monsoon.

21. Relationship between precipitation such as snowmelt, rainfall and runoff is highly nonlinear and complex process and its determination is very important for hydrologic engineering design, flood warning and management of reservoirs for hydropower generation. It is dependent on numerous factors such as initial soil moisture, land use, watershed geomorphology, evaporation, infiltration, distribution and duration of rainfall and so on. Many of the watersheds are gauged to provide continuous record of streamflow data. But situations such as high flood season, instrument failure, etc force the engineers or hydrologists to generate the streamflow records using rainfall and snowmelt by simulation models. Many rainfall-runoff and snowmelt-runoff models such as empirical, lumped and distributed models have been developed and used for simulating the streamflow at the catchment outlet by many researchers. The rivers originate from Himalayas receive a significant flow from snowmelt.

22. Annual rainfall ranges from 1016 to 2630 mm. River Bhagirathi Bhilangana and Balganga are the three major rivers which contribute to Tehri reservoir. Bhagirathi River originates from Gangotri near Gomukh at an elevation of 4255 m and traverses a distance of about 168 Km to its confluence with river Bhilangana at 1.5 Km upstream of Tehri dam. River Bhilangana traverses a distance of 72 Km before meeting with river Bhagirathi. Some minor tributaries like Mangad , Nilapani , Jadganga , Garunganga , Ganeshganga , Asiganga , Dharshugad , Jalkurgad also meet with river Bhagirathi. River Balganga is a major tributary of river Bhilangana, and it meets at Ghansali , 3 Km downstream of Sarasgaon at EL 818m, falling directly into the reservoir. The study basin receives moisture-bearing winds mainly from the Arabian Sea and heavy rainfall during June to September. The annual rainfall of the catchment varies from 1000 mm to 2615 mm. During the period June to September, high flows and floods are experienced in the river. The climatic condition variations are high in the study basin and these are related to changes in elevations and aspect. The rock at dam site consists of the Chandpur Phyllite. Based on lithological characteristics and engineering properties, this has been classified into broadly three grades viz. Grade I (Phyllite Quartize ), Grade II ( Quartzitic Phillite ) and Grade III (Schistose Phyllite). Riverbed consists of large boulders. Average upstream slope of the river is 1:22

23. To compute the flood vulnerable area, a weight linear combination applied in equation: Z = (50 x Discharge) + (14 x Rainfall) + (13 x Slope) + (8 x Drainage density) + (7 x Geology) + (6 x Relief ratio) + (4 x Stream Frequency) Factors derived from modelling simulated for it.

24. Tehri Reservoir Operation Cycle 29 Start of monsoon season is considered as 21 st June and reservoir is depleted to its MDDL EL 740m by this time every year, making a cushion 2600 MCM to absorb flood water of river Bhagirathi. Starting from 21 st June up to 31 st Oct., excess water is stored in the reservoir to achieve FRL . From 1 st Nov. till 20 th June stored water is released as per irrigation and drinking water requirement .

25. Benefits of Stored Water 30 Stored water is released considering the d/s requirements for Irrigation, drinking water and other purposes like Religious Gatherings along the bank of Ganga from Devprayag in Uttarakhand to Allahabad in UP. 300 Cusecs Drinking Water is released for Delhi for about 40 lacs population 200 Cusecs Drinking Water is released for the State of Uttar Pradesh for about 30 lacs population Provide irrigating support to about 8.74 Lac. Hectare land of UP and Uttarakhand states.

26. Prevention of flood 31 Tehri dam, even in the worst scenario can regulate a peak flood discharge approximately twice that of the actual observed till date. Tehri dam, during the floods of 2010, 2011 and 2013, played a crucial role in averting the floods of higher order in the river Ganga by storing the high flood inflows of Bhagirathi.

27. Flood Disaster – June : 2013 32

28. Uttarakhand Flood Disaster - 2013 33 he a v y Disas t er 2 1 3 ca n be a t trib u t ed t o widesp r ead e x c epti o nal l y rainfall across the state from 14-18 June. The entire state hit by heavy (64.5 to 124.4mm) to very heavy (124.5 to 244.5mm)rains resulting into flash floods and landslides in many areas. The districts of Bageshwar, Chamoli, Pithoragarh, Rudraprayag and Uttarkashi were the most affected. The worst impact on human settlements was in Kedarnath Shrine Area, the Mandakini valley , the Alaknanda valley (at Govindghat and upstream), the Pinder valley and along the banks of river Kali in Dharchula area.

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31. Uttarakhand Flood Disaster - 2013 36 recorded Al l th e r i v ers a r e i n spa t e and c a r r yin g a lmost hi g hest discharge. Out of the two major tributaries of river Ganga, Alaknanda flood was uncontrolled whereas most of the flood water of Bhagirathi was absorbed in Tehri dam reservoir. Even then, Devprayag (the confluence town of Alaknanda and Bhagirathi from where Ganga begins), Rishikesh and Haridwar witnessed a historical flood event on 17-June. The role Tehri dam played is explained in coming slides.

32. Flood Control by Tehri Dam at Rishikesh and Haridwar on 16-17 June’ 2013 37

33. Actual Observations at Tehri Dam 38 Actual Peak Discharge of River Bhagirathi on 17-June at Tehri (at 6am) was - 7500 Cumecs (262500 Cusecs) M a x. r el e ase f r om T ehri D a m f r om 1 6 -18 J u n e - 5 00 C um e c s ( 1 7 500 Cusecs) Rise in Tehri reservoir level was 25m in 2 days (16-17 June). At 8 AM on 16-June – 750.00m At 8 AM on 17-June – 764.40m At 8 Am on 18-June – 775.05m

34. 425 425 425 425 425 425 471 593 3 5 3 5 3 5 3 5 3 5 3 5 3 5 3 5 3 5 3 5 3 5 3 5 3 5 5 3 5 5 3 5 5 3 5 5 3 5 5 3 5 5 3 5 5 3 5 5 3 5 5 3 5 5 3 5 5 3 5 5 95 8 1808 31 8 6 2 888 3634 3037 3336 244 3037 3037 3639 7 5 35 7090 6229 5 413 3782 3782 3 2 9 2 3 8 79 42 9 2 4104 2 9 80 2 862 2487 211 2 2112 1 925 1175 3000 4000 5 6000 70 00 80 00:00 2 : 04 : 00 06:00 08:00 10:00 12 : 00 14 : 00 16 : 18:00 20 : 2 2 :00 00:00 2 : 04 : 00 06:00 08:00 10:00 12 : 00 14 : 00 16 : 18:00 20 : 2 2 :00 00:00 2 : 04 : 00 06:00 08:00 10:00 16 . 6.13 17.6.13 18.6.13 D i s c h a r g e i n C u m 2000 e c s 1000 Date and Time Fig-1: Actual observed inflow and outflow at Tehri Outflow from Tehri Reservoir (Cumecs) Inflow Tehri (Cumecs) 39

35. Assessment of Cumulative Flood Impact at Rishikesh 40 Peak Discharge on 17-June was recorded around 8500 Cumecs (when water from Bhagirathi was absorbed in Tehri reservoir) Bhagirathi flow takes about 10 hrs. in reaching Rishikesh. Flood hydrograph of Bhagirathi at Tehri is superimposed after 10 hrs over observed flood hydrograph at Rishikesh to assess the cumulative flood impact. Anticipated max. discharge could have increased to around 15700 cumecs . Change in max. discharge could have further increase the water level about 2.5 to 3.0m .

36. 2110 22 80 27 00 31 5 3700 3 99 9 4179 42 5 9 4419 47 9 9 5 474 6 5 49 77 9 9 8549 8549 8049 729 9 5 9 49 5 774 6124 62 9 9 67 9 9 62 9 9 55 9 9 4649 4179 3 9 49 37 5 3590 3420 22 31 2 5 23 3307 4608 6536 6537 7464 69 4 7 7405 6 8 89 8161 9236 11083 1 5 72 8 15284 139 2 3 123 5 7 9 376 9201 9 061 9 8 23 10 736 10049 8 22 4 70 8 7 6242 5 637 5 437 5 089 4169 20 00 4000 6000 80 10000 12000 140 16000 18000 10:00 12 : 00 14 : 00 16 : 18:00 20 : 2 2 :00 00:00 2 : 04 : 00 06:00 08:00 10:00 12 : 00 14 : 00 16 : 18:00 20 : 2 2 :00 00:00 2 : 04 : 00 06:00 08:00 10:00 12 : 00 14 : 00 16 : 18:00 20 : 16 . 6.13 17.6.13 18.6.13 D i s c h a r g e i n C u m e c s Date and Time Actual observed discharge of Ganga at Rishikesh and anticipated disch. after superimosing Tehri actual inflows with 10 hrs time lag Actual inflow at Rishikesh (Cumecs) Anticipated inflow at Rishikesh if actual inflows at Tehri superimposed with 10 hrs time lag (Cumecs) 32

37. Assessment of Cumulative Flood Impact at Haridwar 42 Peak Discharge at Haridwar on 17-June was recorded around 14500 Cumecs (when water from Bhagirathi was absorbed in Tehri reservoir) Max. water level at Haridwar at 4pm was recorded - 295.90 m (1.90 m above danger level) Bhagirathi flow takes about 12 hrs. in reaching Haridwar. Flood hydrograph of Bhagirathi at Tehri is superimposed after 10 hrs over observed flood hydrograph at Haridwar to assess the cumulative flood impact. Anticipated max. discharge could have increased to around 21500 cumecs . Change in max. discharge could have further increase the water level about 1.5 to 2.0m.

38. 22 41 3446 4843 9 633 9 112 9 166 9 023 8 5 03 99 39 11063 11251 123 2 1 13008 13037 14340 14457 12 95 1 12713 123 2 1 12208 11722 11483 11167 10284 9 6 5 1 8 9 39 8 22 2 8004 7919 7705 2363 36 8 9 5 4 5 1 110 9 1 11949 11704 12307 111 9 12925 13153 13938 1 5 008 162 9 2 1 9772 21 5 19 20331 18009 16140 15748 15145 15246 15420 14917 12 9 09 120 8 8 11001 9909 9692 9 419 84 5 5 20 00 4000 6000 80 10000 12000 16000 2 2 000 2 4 12 : 00 14 : 00 16 : 18:00 20 : 2 2 :00 00:00 2 : 04 : 00 06:00 08:00 10:00 12 : 00 14 : 00 16 : 18:00 20 : 2 2 :00 00:00 2 : 04 : 00 06:00 08:00 10:00 12 : 00 14 : 00 16 : 18:00 20 : 2 2 :00 16.6.13 17.6.13 18.6.13 D i 20000 s c 18000 h a r g 14000 e i n C u m e c s Date and Time Actual observed discharge of Ganga at Haridwar and anticipated disch. after superimosing Tehri actual inflows with 12 hrs time lag Actual inflow at Haridwar ( Cusecs) Anticipated inflow at Haridwar if actual inflows at Tehri superimposed with 12 hrs time lag (Cusecs) 43

39. 35 Lord Shiva Idol at Parmarth Niketan Rishikesh River Ganga along Aastha Path in Rishikesh

40. 36 Flood Situation at Haridwar

41. Flood Situation at Haridwar 46

42. Conclusion 47 Extreme events of cloud bursts are increasing in the Himalayan region drastically. Uttarkhand witnessed 23 such incidents in 2019 against 13 in 2018; Nos. of rain days decreasing and within last decade they come down to 65 from 80; Rainfal l dist r ibu t io n is q u i t e une v en o v er spa c e and t i m e; In the changing scenario of climate change led hydro-meteorological changes we need multipurpose storage dam projects like Tehri dam on each and every major river to - Store surplus water during monsoon to benefit our large population during lean months through irrigation, water supply, hydro power generation etc. Regulate unprecedented floods and saving lives from extreme events like Uttarkahnd disaster of June-2013, M odi f y une v en l y distribu t ed a v ailabi l it y o f w a t e r . Ultimate solution of all these problems is implementation of river linking projects on river systems. 2. Dams 3. CAT 4. Better quality grade anthropogenic activity

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44. A river has a clear focus.   A flood, on the other hand, has no predictable direction.   A flood is generally shallow but does massive damage.