Impact of Environmental Flow on Hydro Power Projects—A Case Study

Large number of river valley Hydro Power Projects (HPP) in Himalayan region are in different stages of implementation. Many of these Hydro Power Projects include diversion structures with long Head Race Tunnel. This results in reduction of river flow in downstream reaches. To keep the river live and to ensure perennial environmental flow in the river, a provision for release of minimum flow called “Environmental Flow” as per the Ministry of Environment & Forest (MOEF) norms are being considered while estimating the design energy of Hydro Power Projects. In India, many Hydro Power projects in the Himalayan region got MOEF clearance with 10% of minimum flow for 90% dependable year as Environmental Flow. As per the latest environmental clearances for Hydro Power Projects from MOEF, the release of Environmental Flows recommended are 30, 25 and 20% of 90% dependable year for Monsoon season, Non-Monsoon-Non-lean season & Lean season respectively. In this paper, a power potential studies have been carried out for Kolodyne HPP-Stage-II (460 MW), Rupsiabagar Khasiyabara HPP (261 MW), Loharinag Pala HPP (600 MW) and Lata Tapovan HPP (171 MW) for earlier and revised Environmental Flow guidelines. With the revised releases of Environmental Flows, the Design Energy for Hydro Power Projects reduces drastically and makes projects unviable in some cases.