CHARACTERISTIC OF WATER LEVEL OF A RIVER BRANCH WITH RETARDING BASIN IN LOWLAND AREA

Abstract

The heavy rainfall occurred in the western area of Gifu prefecture in July 2002. Then, floodwater from the Ohtani River over fixed overflow weir damaged residences in the Arasaki area, Ohgaki City. This river is a small branch connecting to the main river, which has a small bed slope and long recession of water table after rainfall.

In order to make clear the characteristics of this flood, firstly a numerical simulation is applied to this area and the results show overflow phenomena and temporal and longitudinal change of water level. Secondly, the effect of fixed overflow weir and of downstream river improvement were examined for this rainfall event. The results show that peak-cut effect is small due to late peak occurrence of downstream water level and small capacity of retarding basin, and that improvement of downstream river channel is most effective.