Evaluation of environmental flow requirement using wetted perimeter method and GIS application for impact assessment

Abstract The environmental flow requirement varies from project to project based on their location, need, and habitat. The Binwa hydropower project is in the Kangra district of the Himachal Pradesh and a small hydropower project of 6 MW capacity. Here an attempt is made to assess the environmental flow requirement using the hydraulic approach, wetted perimeter method, and compared with the currently maintained e-flow. It is one of the old and commonly used method of assessing the environmental flow based on the hydraulic characteristics such as the depth, width, and perimeter. The discharge is computed for each depth along with the profile and a graph is plotted to obtain the required environmental flow. The assessed minimum flow values are customarily validated using a habitat or holistic approach. Here, to validate the calculated minimal flow value for its sufficiency, the Geographical Information System application is employed as it calculates the vegetation and water indices. The average of the breakpoint discharge has been calculated as 0.7724 m3/s. The minimal flow maintained in the Binwa basin is 0.9 m3/s which is within the limit of the existing flow maintenance during the lean period. The Geographical Information System results support the sufficiency of the environmental flow maintained in the downstream side of the dam. The wetted perimeter helped in deriving the environmental flow while the Geographical Information System application assisted in evaluating the sufficiency spatially.