2015 Volume 30 Issue 3 Pages 161-172
In September 2015, heavy rainfall in the Kanto-Tohoku region caused a levee breach and overtopping at the lower Kinu River Basin near Joso city, leading to severe flood damage. The total rainfall in the upper basin reached about 500 mm. At the catchment of Yunisikawa dam reservoir, initial precipitation of 140 mm was followed by 19.5 mm/h of rainfall (SD, 3.5 mm/h; min-max, 14.0-27.7 mm/h) for 10 h. The observed inflow at Yunisikawa dam reservoir was equivalent to 11.0 mm/h (SD, 0.5 mm/h; min-max, 10.5-11.6 mm/h) for 6 h in the latter part of the period. The objective of this study is to elucidate the flood runoff process with a distributed rainfall-runoff model coupled with a Time-Space Accounting Scheme (T-SAS). Results suggest that representing infiltration losses from soil layers to bedrock was necessary to reproduce the observed hydrograph patterns. Moreover, the T-SAS analysis showed that the source of runoff was changing, even during nearly constant discharge. For instance, contributions from the catchment ridge increased throughout the period.
