巨椋低平流域の都市化と内水 (3) -水害危険度の変化-

Abstract

This paper discusses the changes of flood risk due to urbanization by the form of floodfrequency in the Ogura basin of 52km2 situated in south of Kyoto City. The urban area ofthe basin was under 8% in 1965. But the urbanization is now rapidly going on mainly inhill and high land of the watershed of the River Furu. The urban area has been extendedto 35% in these ten years and anticipated to exceed 50% in the near future. To copewith this tendancy, the improvement of the River Furu was began in 1971 and the Kumi-yama Pump Station with a pump of 30m3/sec was built at the end of the River Furu in 1973.The characteristics of flood runoff and inundation for the past, present and future urbanstates are analyzed by applying the kinematic surface runoff model and the dynamic tankmodel under the several rainfall conditions satisfied the given return periods in one-daydepth and under the given drainage facilities.Noticeable results obtained are as follows:1) The flood risk is increased by the urbanization. For example, the flood risk in thefuture becomes 50 times at a point of the middle reach and 4 times in the lowest paddyfield in the downstream of the River Furu compared with the one in the past, respectively.2) At the present before finishing the river improvement, the flood risk is decreasedslightly in the downstream compared with the one in the past, but increased 30 times inthe middle reach.3) In the future after finishing the river improvement, the flood risk is decreased largelyin the middle reach compared with the one in the past, but increased 3 times in thedownstream and a new counter-plan is demanded.