ENVIRONMENTAL FLOW SETTING BASED ON HYDROLOGICAL INDICES IN UPPER TONE RIVER BASIN RESERVOIRS AND ITS EVALUATION

Abstract

Flow regime alteration causes adverse effects on riverine ecosystem downstream of dams. Changes on 33 statistical indices for flow alteration are studied at 10 reservoirs in the Upper Tone River basin. Minimum flows are decreased and daily fluctuations are enhanced in these reservoirs. Then four types of environmental flow indices - minimum flow, dry flow, low flow and spates- are settled by the rate to median flow based on flow statistics. These indices are derived for 7 types of flow pattern which came out from cluster analysis over Japan. Environmental flow release is simulated to satisfy the four index values in a reservoir and evaluated from flow regime improvement and impact on water usage.