DISCHARGE PROBABILITY DISTRIBUTION AND OPTIMAL PROBABILITY FORM IN THE MAIN EIGHT RIVERS IN KYUSHU TOWARDS EVALUATION OF WATER ENVIRONMENT IN ARIAKE AND YATSUSHIRO SEA

Abstract

 It is important to evaluate the probability of discharge in a water environment since the discharge is effected on the development and occurrence of hypoxia in the coastal area. However, in the previous studies, discharge observational data have uncertainties by the data-scarce and observation method relative to precipitation observational data. Therefore, few studies have evaluated the probability of discharge. Thus, this study aims to reveal the optimal discharge probability distribution in each river basin with d4PDF by developing the runoff model which is considered the inundation based on the current river channel in the main eight river basins in Kyushu. As a result, it is found that the goodness of fit of the Gumbel distribution which is used for precipitation distribution evaluation widely is also high in the discharge. However, it is suggested that the evaluation of optimal probability distribution in each river basin is important since there is the case that it is different in a river.