BASIN STUDY FOR ENVIRONMENTAL FLOW ASSESSMENT IN HYDROPOWER DEVELOPMENT

Abstract

Most of the world energy demand is fulfilling with non-renewable and pollutant sources such as oil, coal and gas. Hence, more inversions are given to hydropower production to reduce greenhouse emissions and provide sustainable energy production. In a River basin, different hydropower scheme can be developed like 'storage dams, run-of-the river scheme or pumping stations. These hydropower developments have significant impacts in the river ecosystem, reducing the total amount of flow and affecting both; the seasonality of flows and the size and frequency of floods. These changes in discharge patterns affect the abundance, species composition and viability of aquatic life in the river. The aim of Environmental Flow (EF) is to enhance the management of river flows to ensure the sustainability of river ecosystem and provide a reliable tool for water allocation decisions, in this case between hydropower production and ecology needs. A common practice in reservoir operations is releasing a minimum fixed amount of water throughout the year, commonly 10% or 15% of 90% dependable flow. This amount of water may or may not sufficient for maintaining aquatic life downstream of dam. Environmental Flow Assessment (EFA) techniques are beyond of this old practice and studies have demonstrated that keeping modified flow regime in the river, rather than a fixed amount of water is more beneficial for downstream ecosystem (Waddle, 1992). The present study focuses in various EFA techniques; based on a review of international literature and studying environmental flow practices from various parts of the world and these techniques are applied in two cases of study located in India. The first case study is located in Lohit river basin in Arunachal Pradesh. The river basin development is under cascade scheme with six proposed storage dams and power houses at toe of the dam. The second case study is located in Pabbar River basin in Himachal Pradesh. The project is run-off the river scheme which creates a dry river stretch of 11.55 km between diversion point and power house. For every dam site in both cases of study; environmental flows are given and minimum flows are proposed under different seasons throughout the year. The hydrology and hydraulic characteristic of the rivers are linked with fish water requirements for different Himalayan fish species available in the river, based on water depth and water velocity habitat parameters.