Probable Downstream Impacts of 2000 MW Lower Subansiri Dam in Arunachal Pradesh of North East India

Downstream of River Subansiri showed a biologically controlled healthy ecosystem along with riparian zones and catchment forests which are hot spots of species before the hydel projects were undertaken. This important natural corridor for the energy flow, nutrient cycling and species diversity would certainly be altered due to the construction of 2000 MW lower Subansiri dam in three orders viz., first order impact (hydrology) through alteration in the flow regime, discharge control resulting from damming of river, reduced flow variability and total volume of runoff, and water quality (physical, chemical and biological changes). Second order impacts through changes in sediment transport, floodplain morphology, river water turbidity affecting the biota directly, alteration in primary production (plankton, riparian vegetation), and the third order impact through the habitat degradation due to changes in flow regime, water quality, loss of breedingground for threatened fishes like Tor tor, Tor putitora, fish diversity, fishery production, creating barrier for upstream and downstream migratory fishes as well as endangered aquatic mammal Platanista gangetica, loss of genetic diversity of indigenous deep water rice varieties as well as important native species and thereby affecting the food production capacity and livelihood security of the people who depend on the downstream.