INTERPRETATION OF THE RIVER BED PROFILE CHANGE AT THE DOWNSTREAM OF A DAM USING AERIAL PHOTOGRAPH

Abstract

Since continuous information of the river bed degradation in the past is rare, it is hard to acquire the quantitative feature of the degradation process. Thus, in order to hindcast the degradation process in the river bed at the downstream of a dam, we estimated the past river bed elevation by using a series of aerial photographs

The river bed elevation was analyzed at the downstream of Kawamata dam completed in 1966. Due to the stop of the sediment supply to the downstream of the dam, the river bed degradation proceeded quickly at the section which is close to the dam, but the river bed rose at the further downstream section from 1966 to 1976. Large floods which occurred during 1976 to 1983 caused degradation even in the further downstream section. However, the river bed degradation stopped in around 1983 (after the dam completion), and the river bed has been stable afterwards. A final amount of river bed degradation was 2-3m. The historical change in bed profile estimated by aerial photograph helps us understand the variation process of river bed topography at the downstream of dams.