No abstract

Flood runoff models of urbanization from farmland based on the physical characteristics of a basin have been minimally used in previous research until today. Consequently, the runoff analysis has not been performed that is based on physical basis. Therefore, this research undertook flood discharge analysis from urbanization using the unit flood discharge concept that is enhanced the previous research. The study area was selected at the Kurabe River basin, which is 17.5 km 2 in area having a very steep landscape. Twenty-one rainfall events at 10-minute intervals were selected, and five urbanized years were tested. From 1976 to 2009 during 35 years, the flood discharge increased approximately 2.0 times, in which residential areas increased from 23% to 48%; the maximum specific discharge was 21.7 m 3 ·s −1 ·km −2 in a some block, which is a remarkably large amount. Furthermore, following issues investigated: changes in the hydrograph were associated with urbanization, the effect of a small reservoir aiming to cut down the peak discharge and the relationship between the unit discharge, and the relationship between our method and the discharge estimated by a "Rational Formula". In particular, the effect of the small reservoir for flood control was found to be remarkably efficient. Finally, the validity of our method was confirmed at the study area in the observed discharge. This result is very useful for estimating runoff discharge changes by urbanization from farmland.

Recently severe damage of flooding by urbanization was frequently occurred. To prevent this damage, small reservoir was constructed in the urbanized residential area. This paper describes an effect of flood peak discharge control by a small reservoir (control reservoir) caused by rapidly developed urbanization. Although work for this purpose was conducted, research on the effects of the control reservoir was not conducted until now. This research, conducted by simulation, was a case study in the Kurabe River Basin in the Tedori River Alluvial Fan Area, Japan, based on the precise investigation of the reservoir in the actual field. The study was conducted to determine not only the actual control reservoir capacity for the newly developed residential area but also the ideal capacity for all present residential areas and the largest capacity allowable for a maximum rainfall event that recently occurred. The control reservoir effects between individual blocks and the entire basin area were compared by dividing the test basin into 15 blocks (sub-basins). The results showed that the effects on the capacity per unit area of the residential area in blocks have close relationship with the decreasing ratio of peak discharge in blocks. Consequently, the effects of control reservoir capacity and the limitation were clarified. In the future, control reservoirs should be constructed for all of the already developed residential areas, for example, by utilizing underground car parking lot. The results of this research can contribute to the design of the control reservoir for protection against flooding damage in urbanized areas.