1. Keshav Deshmukh, General Manager (D&E) NHPC Ltd., Faridabad, India

2. NHPC Ltd.-OVERVIEW  NHPC Limited, a Govt. of India Enterprise, was incorporated in the year 1975 with an objective to plan, promote and organise an integrated and efficient development of hydroelectric power in all aspects.  NHPC has become the largest organization for hydropower development in India with capabilities to undertake all the activities from conceptualization to commissioning in relation to setting up of hydro projects.  NHPC Limited presently has an installation base of 6507 MW from 20 hydropower stations on ownership basis including projects taken up in Joint Venture.  The Hydropower power stations of NHPC are located in following hilly states of India.

3. Sno.StateNo. Of Operating Power Stations 1Jammu & Kashmir7 2Himachal Pradesh5 3Uttarakhand2 4Sikkim2 5West Bengal1 6Manipur1 7Madhya Pradesh (JV)2  NHPC Limited is presently engaged in the construction of 4 projects aggregating to a total installed capacity of 3290 MW. Given the renewed thrust on development of hydro power in the country, NHPC Limited has drawn up a massive plan to add about 10,000 MW of hydropower capacity by the end of XIII plan (year 2022).

4.  In geomorphology, a river is said to be rejuvenated when the base level that it is flowing down to is lowered. Rivers are always attempting to reach a state of dynamic equilibrium where erosion, deposition and transportation are in perfect balance.  Rivers that have this form of profile are at an equilibrium with the environment.  In recent times, river health is being deteriorated significantly due to pollution from industrial and domestic waste, fertilizers and pesticides.  Restoring the rivers to their original state has become the need of the hour as changes in water quality, discharge and sediment load are constantly having negative impacts on sustainable development. RIVER REJUVENATION

5. ENVIRONMENTAL FLOWS  Environmental flows are those flows that are needed to maintain aquatic ecosystems, renewable natural resources production systems and associated livelihoods.  The different components of an environmental flow regime contribute to different ecological processes.

7. NEED FOR STORAGE IN RIVER REJUVENATION AND E- FLOWS  India is blessed with a rainfall pattern that is distributed over 4-5 months in the year and that too in only a few hours of these months.  Because of the sporadic spatial and temporal distribution of precipitation, the only way water supply can be controlled to match demand is through storage. Seasonal variations and climatic irregularities in flow impede the efficient use of river runoff, with flooding and drought causing problems of catastrophic proportions.  Dams clearly make a significant contribution to the efficient management of finite water resources that are unevenly distributed and subject to large seasonal fluctuations.

8. Map showing the spatial variability of Annual rainfall

9. 9 Temporal variation of rainfall

10. Water Scenario in India Reducing per capita water availability Per capita water availability in m 3 /year Water stress 1700 m 3 /capita/year Water scarcity 1000 m 3 /capita/year

11. Map showing Per Capita Storage created in different countries of the world

12. CASE STUDY OF DIBANG MULTIPURPOSE PROJECT, ARUNACHAL PRADESH IN VIEW OF RIVER REJUVENATION AND E- FLOWS

13. Rejuvenation of the river in respect of storage projects can be broadly classified under following objectives: (A)Flood moderation in the river thereby providing protection against disastrous floods in the downstream. (B)Enhancing the lean season flow of the river which further rejuvenate the river with respect to sustainable development of flora, fauna and associated eco-system health. In case of ROR projects, it is difficult to maintain a certain amount of discharge in the downstream during lean season, where as in case of storage project the lean season flows can be increased substantially. The applicability of above aspects in case of Dibang Multipurpose project has been represented in subsequent slides.

14. PROJECT BRIEF  Dibang Multipurpose project is proposed across Dibang river, a major tributary of Brahmaputra River, near Munli village in Dibang valley district of Arunachal Pradesh.  Dibang river originates in India from snow covered Himalayas close to Tibet border (at El 5000 m).  The project envisages construction of 278 m high concrete gravity dam across Dibang River and having reservoir storage of 3248 Mcum and reservoir surface area of 35.64 sq.km at Full Reservoir Level.  Dibang Multipurpose project has been conceived with a dual objective of flood moderation and electricity generation.

15. A VIEW OF DIBANG RIVER UPSTREAM OF DAM 15

16. CATCHMENT PLAN OF DIBANG MULTIPURPOSE PROJECT

17. (A ) EFFECT OF PROJECT DEVELOPMENT ON FLOOD MODERATION  Flood moderation through the project is proposed in the event of occurrence of a 100 year return period flood wave preceded and succeeded by a 25 year flood wave at dam site.  Release from the reservoir has been restricted to 3000 cumec, which was considered by Brahmaputra Board as the safe carrying capacity of the downstream channel reach.  It was found that the storage of the order of 563 Mcum and 340 Mcum is required for passing 1 in 100 year return period flood and 1 in 25 year return period flood respectively.  Accordingly, the rule curve was adopted for reservoir of Dibang M.P. Project to achieve the desired benefits of flood moderation. Contd..

18.  Flood routing study has been carried out downstream of dam for 1 in 100 year return period flood (12756 cumec), 1 in 25 year return period flood (9750 cumec) and 3000 cumec discharge to assess the impact of flood moderation d/s of dam.  Hydrologic Engineering Centre software HEC-RAS 4.1.0 has been used for hydro-dynamic modeling.  It was found that 45% of reduction in top width/area is envisaged due to flood moderation.  The relief in water level is of the order of 1 to 2 m beyond 20 km d/s of dam for 1 in 100 year flood, which is quite significant considering the fact that Dibang is quite a wide river in these reaches.  The plots showing variation in depth, water level, velocity and topwidth are shown in subsequent slides:

19. Variation in Depth for Different Discharges

20. Water Level Variation for Different Discharges

21. Variation in Velocity for Different Discharges

22. Variation in Top Width for Different Discharges

23. (B) ENVIRONMENTAL FLOWS IN VIEW OF STORAGE PROJECTS  In case of Dibang multipurpose project, dam operations have been proposed in such a way that natural lean season flow is enhanced for river rejuvenation.  The effect of peaking operation of Dibang project on water level fluctuation in the downstream especially on Dibru-Saikhowa National Park was studied. The location of Dibru-Saikhowa National Park w.r.t. Dibang Multipurpose Project is shown in subsequent slide.  During monsoon season due to availability of high discharge in the rivers, Dibang Multipurpose project shall operate through most part of the day to produce the power and thus there will not be much flow variation downstream of the project due to regulation for power generation. Contd..

24. Map showing location of Dibang Multipurpose project w.r.t. Dibru-Saikhowa National Park Dibru-Saikhowa National park

25.  However, during the lean season months, i.e. from November to February, when the river discharges are considerably reduced, it is proposed to operate at least one turbine out of 12 turbines at 80% load continuously.  In addition to this, 15 cumec environmental flow shall be released from the dam.  This essentially means that in the worst possible scenario, the project will release only 15 cumecs as environmental flows supplemented by release of water by the operation of one turbine at 80% load continuously.  Thus, the lean season discharge gets enhanced by about 20% in comparison to natural lean season flow.  A study carried out to assess the fluctuation in water level, flow, velocity and topwidth at different reaches d/s of TRT along the river shows that the fluctuations in these parameters due to Dibang MPP are almost negligible considering the size & morphology of the river.

26. Effect of peaking on W.L. variation

27. Fluctuation in W.L. at u/s of Lohit confluence (Pre & Post project scenario)

28. Fluctuation in Topwidth at u/s of Lohit confluence (Pre & Post project scenario)

29. Fluctuation in Velocity at u/s of Lohit confluence (Pre & Post project scenario)

30. It is noteworthy to mention here that the storage dams have been instrumental in minimizing the devastation in the downstream areas caused due to floods: (a) Tehri dam in Uttarakhand saved the city of Haridwar and Rishikesh in the downstream from the fury of flash flood during 16-17 June 2013. A report said the fury of nature in Uttarakhand was such that waters rose as high as a four-storey building at Devprayag, where Alaknanda and Bhagirathi meet, in a 24-hour period after the cloud burst. The rise at Devprayag, Rishikesh and Haridwar could have been much higher if the flow of Bhagirathi was not contained by the Tehri reservoir. It was seen during studies that in the absence of tehri dam, the flood peak at Haridwar would have been about 21500 cumec in place of actual observed about 14500 cumec. Hence due to Tehri dam the flood at Haridwar was mitigated by about 7000 cumec. (b) The Wular lake in Kashmir also prevented flooding in the downstream areas during September 2014 floods.

31. CONCLUSION  Rapid growth of industrialization and urbanization and rising standards of living has exposed water resources to various forms of degradation.  Creating water storage would go a long way in leading to river rejuvenation by augmentation of e-flows especially during lean season by considered dam operation strategies.  It can be seen from the above case study of Dibang Multipurpose project that velocity/flow fluctuation in the downstream of dam is insignificant due to peaking operation. This could be achieved by proper planning of dam operation strategies.  In a long-term perspective, green growth is growth without unsustainable deterioration of the environment or growth with ‘modest’ negative impact on the environment in the short term and hydropower growth comes under this green growth category.

32. CONCLUSION  Any development,big or small, has some impact on the environment. A crucial decision concerns the desired condition or level at which the eco- system of the region is to be maintained.  Sustainability concept suggests that we need to maintain the eco-systems so that they yield the greatest benefit to the present generations, while retaining the ability to meet the needs and aspirations of future generations.  There is a need to accelerate the development of new water storage projects for multiple purposes. Reservoir regulation must be optimised to store more flood waters while considering the requirements of upstream and downstream areas.  Storage projects are also needed for creation of water security which can be put to multiple use. Hydropower could be one of the incidental benefits for these storages.