Ecological Flow Requirement for Fishes of Godavari River:Flow Estimation Using the PHABSIM Method

Fish habitat requirements are an essential aspect of the estimation of environmental flows. In India, a few studies have proposed environmental flows for the major rivers on the basis of qualitative observation or expert opinion. As part of a study regarding the effect of altered flow across the Godavari river on fishes, we estimated flow requirement of the fishes using a physical habitat simulation model (PHABSIM). This model uses habitat requirement of selected fish species in the form of habitat suitability curves (HSCs) against river habitat availability. We developed HSCs for five economically important fishes (Bangana dero, Cirrhinus cirrhosus, Labeo calbasu, Labeo fimbriatus and Wallago attu). These HSCs indicate that B. dero prefers high velocities (0.9–1.2 m/s) compared with the other species and that L. fimbriatus prefers deeper areas (1.2–1.5 m). C. cirrhosus uses low flows with moderate depth (0.3–0.6 m/s; 0.6–1.5 m). The HSCs were used in PHABSIM along with instream habitat data recorded from four cross-sections to predict the weighted usable areas (WUAs) of the fishes. The relationship between habitat area and discharge was used to predict the minimum acceptable flow for maintaining fish habitats. On the basis of the WUA–discharge relationship curve, 26% of the mean flow was recommended as the minimum ecological flow required below the Polavaram dam of Godavari river.