Development of Residential Areas and Flood-Disaster in Yodo River Basin

Abstract

The chief aim of this report is to examine into the causes of flood-disaster, the system of construction for prevention of such disaster and the method of reformation. Above all this author has laid emphasis on analyzing the changes into residential areas of the river basin.According to the chronicle history of the respective cities along the Yodo River basin, and to that of the Yodo River Improvement Office, and judging from the height of settlement built there, it is found that the recent floods were frequently caused on the right side bank of the Yodo River, by a breakdown of the embankment of its tributaries mainly in the area of the upper stream at a distance of one kilometer from the junction of two rivers. The left bank of the Akuta River is particularly dangerous in the “Uchimizu” zone of the tributary region. To the left bank of the Yodo River, the low ground of the right bank of the Amano River has a high ratio of danger. It was brought to light, that this is due to the insufficient drainage capacity of river water, overflow areas, and poor capacity of the draining pump in the “Uchimizu” zone.The expanding tendency of changes into residential areas of the river basin has gradually found its way near the flood plain and is becoming the most dangerous area. Furthermore, the utilization of low land for building land by Prefectural authorities and public corporations as well as by medium and small building companies, have been reasons for the advance in land prices.Compared with the newly-built constructions, the old ones are found to be built in the safer sense, as their heights are just in line to safely cope with the ‘flood line’.Thus old constructions were built on natural levees, reinforced with stone-walls and with level-raised ground on the embankment, so that they might be safer from floods. On the contrary, the newly built houses are very close to each other; even their foundations one laid close to each other on the back-marsh, as if the builders were quite indifferent to the danger of floods. These facts increase the ratio of danger considerably; also the insufficient drainage system against flood, which may break out at any time during the rainy and typhoon seasons.