Environmental flow assessment for the Musi River, India

The survival of the flora and fauna in rivers depends on maintaining environmental flow (e-flow). In the present work, e-flow has been calculated for two gauging sites of the Musi River, Hyderabad, India. The study applies hydrological methods such as the Tenant method, Tessman method, flow duration curve, median flow method, mean annual flow method and dynamic method for the assessment of e-flow in the Musi River. The Tessman method provides the e-flow estimate, ensuring good to excellent habitat conditions throughout the year. The flow duration curves yielded relatively low estimates of e-flow, indicating poor e-flow conditions. The results obtained from the hydrological methods can be used as preliminary estimates for comparing e-flow obtained from hydraulic or habitat methods. The flushing flow as recommended by the central water commission was calculated as 121.6 m³/s and 809.6 m³/s for the Damaecherla and Wadapally gauging sites of the Musi River. Due to the alteration in flow caused by the operation of the Osmansagar and Himayathsagar reservoirs, the flushing flows have a return interval of greater than 8 years in the Musi River. This denotes an exorbitant threat to river health and poor stream load-carrying capacity. Releasing discharge equivalent to flushing flow from reservoirs at least once a year is indeed a highly recommended practice in river management, especially for maintaining e-flow.