Changes in Aquatic Ecology and Diversity After Construction of Hydro-Electric Power Projects on River Ganges in Garhwal Himalaya, India

River Ganges is one of the important river of Indian subcontinent. This river originates in Gomukh Glacier in Uttarakhand State of India and merges into Bay of Bengal.  44 hydroelectric project have been planned all over Uttarakhand.  18 of these are within first 100 kilometers from the origin of river Ganges, located in Tehri and Uttarkashi districts of Garhwal Himalaya.  Two projects – Maneri  Bhali Phase I -  Phase II and Tehri Dam have already been constructed.  Because of Maneri Bhali phase I- phase II  hydro electric project, a stretch of approximately 29 km between Uttarkashi & Dharasu is virtually dry because of diversion of water into the turbines.  These hydroelectric projects are having a major impact on aquatic ecology and diversity of river Ganges in this stretch because of major fluctuation of water level. Our study documents the effects of these dams on the biotic & a biotic environment of river Ganges within the range of these hydroelectric projects.

Data presented here is from one site – Manari Phase I-Phase II.  The results on water temperature show a clear increase in average water temperature.  The temperature range before the dam wall was 14 to 10 degree centigrade (⁰C) while after the Dam wall the temperature ranged from 18 to 8 ⁰C in the same area.  Similar pattern was observed in case of dissolved CO₂ and DO.  Before dam average CO2 ranged was 4.47±0.01 while after dam it was 5.5±0.01.  DO before dam wall was 9.8±0.1 while after dam it became 7.1±0.05.  The native snow trout (Schizothorax species, Cyprinidae) population estimated before and after dam also varies. Six sampling on the sites gave an average number of 98±9 fishes of different sizes before dam while it was 38±5 fishes after the wall.  Variations in population and abundance of various phyto-planktons and zoo-planktons were also observed.

The results clearly indicate a massive shift in physico-chemical characteristics of water before and after Dam Wall.  This in turn is responsible for declining fish population of native snow trout (Schizothorax species) and alterations in phyto-plankton and zoo-plankton species.  The survival of fish itself will depend on the physico-chemical parameters and the population of phyto & zoo-planktons, which are changing drastically.  Steps to monitor the situation need to be taken fast otherwise this will result in catastrophic effect on the general aquatic population after the dam wall in Manari Phase I- PhaseII Project.