Effect of Previous Flood on Suspended Sediment Transport during Rainstorm Runoff

摘要

Suspended sediment transport during several rainstorm runoffs were investigated on two watersheds of different land use in Hokkaido, northern Japan. One watershed is entirely forested, while the other is 35% agricultural land. The main agriculture in the area is of upland crops, dairy fanning, and beef cattle pasturing. The behavior of suspended sediment transport was examined on both watersheds. The load of suspended sediment from agricultural watershed exceeded that of forested watershed. This reflects the difference of land use. The mechanism of suspended sediment transport was studied in terms of several hydrological factors. It became clear that the concentration of suspended sediment during rainstorm runoffs could be explained from two hydrological factors: the peak river discharge, which is an index of rainstorm runoff scale; and the D_2 factor, which can be calculated from the scale of the period since the previous flood. It was considered that the changing size of the source area of streamflow during rainstorm runoff influences the source location of suspended sediment in the watershed.