Ryosuke OKA
Evaluation of flood arrival time by using distributed runoff model
Minjiao Lu
Under the heading of "Evaluation of flood arrival time by using distributed runoff model", a study was conducted. This distributed runoff model was based on Nakagawa formula: Tc=3.8¡ß10-4{Lmax+A(2Lmax)-1SLmax-0.3Rv-0.4}. Basin model was analyzed from only one river; therefore the evaluation of the reproducibility of the river to the other is insufficient.
In this study, Nakagawa formula was expressed and calculated by the flood arrival time for seven rivers including: Rumoigawa, Kurokawa, Kariyadagawa, Shibumigawa, Hayadegawa, Kitagawa, and Dokigawa, flood peak of the hydrograph was the true value which the author compared to the performance of time.
The analysis method using Nippon KOEI-Geographic Information Analysis System (hereinafterreferred to as NK-GIAS) and the analysis of geographic factors required for calculating formula, therefore they were determined flood arrival time. In comparison with the true value and each calculating formula, there was significant difference of flood arrival time. There was also no uniformity of flood arrival time in each river. Although it was not a good result, the expressions of Nakagawa and Kadoya have the same level of accuracy.In the comparison between Doki and Rumoi rivers in the hilly forest area, they were 1?hour-error and 2-hour-error for Doki and Rumoi respectively.. Therefore, it was found that the accuracy is significantly different by basin.
As future prospects, watershed constant of Kadoya formula is 290 for the hilly forest area. Nevertheless, it is necessary to perform analysis of watershed e.g the small urban watershed constant.
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