Prediction of Dam Construction Impacts on Annual and Peak Flow Rates in Kase River Basin

Abstract

The SWAT model has been used to estimate the impact of dam constructions on annual and peak stream flow rates in Kase River, Japan. A new multipurpose dam, Kase River dam has been constructed just downstream of another old agricultural dam, Hokuzam dam. The watershed area is set up 197.735 km 2 that accounts for 54% of the entire area of the Kase River Basin. The model was calibrated and validated for stream discharge data from 2008-2009 by using Nash-Sutcliffe to model performed evaluation. Simulated data from the model for the period 2008-2009 were used in order to investigate the response of stream flow to dam constructions in Kase River basin. Using sensitivity analysis dominant parameters affecting water flow, the four most sensitive parameters of flow were selected and adjusted. The best fit was achieved with R 2 = 0.86 and NSI= 0.84 at Furuyu outlet just downstream after the new dam. The result from the scenarios analysis shows that an annual runoff decreases consistently from the disappearance of dam by the value of 1.40-11.59 m 3 /s to 0.83-8.89 m 3 /s and 1.18-11.35 m 3 /s respectively during appearance of Hokuzam dam only and appearance of Hokuzam and Kase dam in the watershed. Since both dams' impoundments, peak flow rates at Furuyu have decreased by 23.45% from current condition. The results of this study enhance the understanding of stream flow consequences of dam constructions associated with impoundment, while these estimates could aid a decision maker to optimize water supply and demand and further water quality management in this basin.