Abstract
Flood control plans by reservoir in small urban basins generally assume a case of occurring uniform rainfall in the catchment. However, the spatial distributions of rainfalls are extremely different especially for thunderstorms, and it is impossible to specify the area of concentration for each precipitation. The reservoir connecting catchments makes areal deviation averaged so that more effect of flood control is expected. Such reservoir could achieve not only the same effect of flood control as a bigger single reservoir but also more effect than a single reservoir having the same capacity.
