Eco-system Benefit Rendered by Large Hydro Projects of India & Consequential River Rejuvenation
Dr. B.P Das Expert Consultant FAO, UN Former Engineer In Chief & Chief Advisor Department of Water Resources, Odisha Former Vice Chairman, EAC for River Valley & HE Projects, MoEF Chairman, Expert Body for studying Uttarakhand Disaster, MoEF
Brain Storming Session-1 ROLE OF WATER STORAGE IN RIVER REJUVENATION AND SUSTAINING E-FLOWS
Ecosystem benefit rendered by large Hydro Projects of India and Consequential River Rejuvenation Dr. B. P. Das Former Chief Advisor & Engineer-in-Chief, WR, Odisha Former Vice Chairman, EAC for River Valley & HE Projects, MoEF Chairman, Expert Body for studying Uttarakhand Disaster, MoEF Chairman, Monitoring Committee, Indira Sagar & Omkareswar Command Area in Narmada Basin, MoEF Expert Consultant to FAO
April 5, 2016
General Note ď Ž
Dams constructed across rivers for multiple uses result in abstraction of a large proportion of freshwater to meet consumptive use. Consequently the riverine reach below the dam gets deprived of its need to sustain the aquatic ecosystem particularly in lean season. While this is generally true for heavily harnessed rivers in arid basins, such as AmuDarya, Syr-Darya draining to Aral Sea, Colorado, Indus and Nile the situation is absolutely different for tropical rivers in India in general and peninsular rivers in particular. The benefit to the river for sustaining aquatic biodiversity and general riparian use is presented for a few typical multipurpose projects of India.
General Note ď Ž
For rivers harnessed in peninsular India, 20% of MAF flows in non-monsoon in the riverine reach below dams against 510% MAF that was flowing prior to construction of dams. This is substantiated by reference to pre and post dam hydrological scenario for two large dams in Odisha, Hirakud Dam on Mahanadi and Rengali Dam on Brahmani, Nagarjuna Sagar and Srisailam Dam on Krishna.
ď Ž
Positive contribution of major dams in India to riverine health and sustenance of aquatic ecosystem in addition to enhancing the capability of the downstream reach to meet industrial / drinking water need and flushing out pollutant is established. For major dams almost 32-50% of the monsoon flow gets impounded in reservoirs & stored water at end of monsoon gets released after power generation synchronizing with Rabi / Summer irrigation need of the downstream. The estuarine region of the harnessed river is particularly benefited.
General Note Benefit of Farakka Barrage The Farakka Barrage across river Ganga in Murshidabad district of West Bengal was constructed in 1970 to replenish the freshwater flow in river Hoogly for improving navigability to Calcutta port. The feeder canal from Farakka brought in 850 m3/s perennially into Hoogly estuary, feeding the Sundarban mangroves, which forms the largest chunk of 4,000 km2 in India. ď ŽAs Ganga (Padma) flowed to Bagladesh causing dearth of freshwater the mangroves were slowly perishing, with salinity increasing to 30-35 ppt, detrimental for the mangroves. With increased freshwater flow from Farakka barrage, not only the mangroves flourished due to decrease of salinity by 10-15 ppt but also the fishery production went up from 7,000 Ton (1970) to almost 70,000 Ton currently attributable to the healthy mangroves in the Sundarban. ď Ž
Mahanadi Basin Hirakud Dam
Non-monsoon Flow Below Hirakud Dam Hirakud Dam intercepts 83000km2 of 1,48,000km2 of overall basin Mean Annual Flow 50 MAcft Monsoon Flow 47 MAcft Non-monsoon (without Hirakud Dam) 3 Macft Non-monsoon flow (1957-97) deduced from Hirakud data 2.023 Macft Post Dam non-monsoon flow actual(1958-97) 5 Macft
Comparison of actual/derived flow at delta head in pre & post dam situation
9.000
7.000 6.000 5.000 4.000 3.000 2.000
Ye ar Pos t Dam
Pre Dam
1996-97
1994-95
1992-93
1990-91
1988-89
1986-87
1984-85
1982-83
1980-81
1978-79
1976-77
1974-75
1972-73
1970-71
1968-69
1966-67
1964-65
1962-63
0.000
1960-61
1.000 1958-59
Runoff in M Acft
8.000
Brahmani River Basin 84°
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LEGENDS # Urban Area 1 Sub Basin Number Sub Basin Boundary State Boundary River/ Drain/ Water Body
Debagarh #
Gohira N. Rengali Reservoir
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Non-monsoon Flow Below Rengali Dam Rengali Dam intercepts 25,250km2 of 39,268km2 of overall basin Mean Annual Flow 20,000Mm3 Monsoon Flow 18,000Mm3 Non-monsoon (without Rengali Dam) 2,000Mm3 Non-monsoon flow(1980-2002) would have been 1123Mm3 Post Dam 6000 non-monsoon Comparison of actual/derived flow at flow actual(1980-2002) 3434Mm3
delta head in pre & post dam situation
5000
3000 2000 1000
Year Pre Dam
Pos t Dam
2001-02
2000-01
1999-00
1998-99
1997-98
1996-97
1995-96
1994-95
1993-94
1992-93
1991-92
1990-91
1989-90
1988-89
1987-88
1986-87
1985-86
1984-85
1983-84
1982-83
1981-82
0 1980-81
MCM
4000
Krishna River Basin
Nagarjunasagar dam
Non-monsoon Flow Enhancement in Krishna Basin
Basin Area – 258948km2 Annual yield of Krishna River – 78100Mm 3 (CWC) Bachawat Award(1976) accepted 75% dependable yield as 63900Mm3 Non-monsoon flow of Krishna River – 6409Mm 3 Two Mega Projects in Andhra Pradesh
Nagarjunasagar intercepts 215192km2 Mean annual flow 42360Mm3 (CBIP) Live storage of 6940Mm3.
Srisailam intercepts 2062422km2 Mean annual flow 52160Mm3 Live storage of 7080Mm3 Major Projects in Karnataka Hipparagi Barrage, Alamatti Dam, Narayanpur Dam, Tungabhadra Dam Major Projects in Maharastra Koyna Dam
Post monsoon Study of Krishna Basin Nagarjuna Sagar (Operational 1974) As on 31st Oct. live storage available is 6940 Mm3 Srisailam(Operational 1984) As on 31st Oct. live storage available is 7080 Mm3, Which flows down to Nagarjuna Sagar excluding an abstraction of maximum 200 Mm3 in the non-monsoon Consumption Rabi requirement for ultimate command areas of 1 Mha of Nagarjuna Sagar is about 2000 Mm3. Overall flow available at Nsagar is around 13000Mm3. Average flow below Nagarjunasagar Dam upto Krishna barrage
Non-consumptive water available Add D/S contribution of 44000km2 and return flow
11000Mm3 3500Mm3
On the average almost 10-12000Mm3 flows from NSagar dam to Krishna barrage at Vijayawada (in the post 1985 period) against 7000Mm3 prior to construction of the dam helping the aquatic environment and significantly stabilizing the delta command.
Enhancement of Non-monsoon Flow in Krishna Basin Non Monsoon Flow Pattern in Krishna River below NS Dam 3500 3000
2000 1500 1000 500
Pre Dam
Post Dam
Jun
May
Apr
Mar
Feb
Jan
Dec
0 Nov
Flow in MCM
2500
Conclusion
Hydrological basin studies of three major east flowing rivers, Mahanadi, Brahmani and Krishna have been presented. It is clearly established that in predam situation the tail reach of the rivers used to convey 5 to 15% of the annual flow with insignificant flow during summer months March through June. After impounding by the dams the non-monsoon release and the downstream basin contribution have resulted in substantial increase (20-25% of the mean annual flow) helping the aquatic environment of the entire riverine reach in the downstream. The major dams are thus contributing positively to river rejuvenation and aquatic environment.
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