An Analysis on the Variation of Long-Term Runoff Characteristics of Basin before and after Dam Construction II. An Analysis on the Variation of Long-Term Runoff Characteristics of Basin Using Model Parameters Estimation

The purpose of the present study was to evaluate the changes of long-term runoff characteristics of a large river basin due to construction of a large multipurpose dam using NWS-PC Model, which was simulated with rainfall data, evapotranspiration data and phisiographic data. The phisiographic Parameters of the model are obtained from the established GIS data base and some parameters to account for the changes of natural environment are quantified from remote sensing film taken before and after reservoir construction. Rain and observed runoff data of the year, 1974, were used to calibrate the model. After having calibrated the model by trial and error method, runoff characteristics of 9 years before and after dam construction were simulated, From the simulation results, the relative error of calculated discharge to observed discharge was found to be within approximately 10%. Therefore, the model was considered to be adaptable for the present study, and the changes in long-term runoff characteristics were evaluated based on the runoff computations. In conclusion, it was found that runoff ratio of watershed upstream of the reservoir is slightly increasing due to the changes of natural environment, and the flood peak flows are attenuated due to storage effect of the reservoir, wheres, low flows are, on the average, increased due to regulated outflow releases from the reservoir.