Rainfall, runoff and sediment yield were observed at four small watersheds to study difference of the sediment yield characteristics with natural recovery of vegetation in granite hilly mountain. These watersheds are forested watershed (A watershed), vegetation recovery watershed (B watershed), 85% forest recovered watershed (C watershed) and 50% forest recovered watershed (D watershed). The soil depth of A watershed is deeper than those of three other watersheds and that of C watershed is especially shallow. Perennial flow has observed at A watershed while ephemeral flow has observed at three other watersheds. High peak discharge and much sediment discharge have observed at D watershed while low peak discharge and little sediment discharge have observed at A watershed. In all watersheds, increasing of peak rainfall was followed by increase of peak discharge. The rate of increase in peak discharge to increase of peak rainfall of B watershed and D watershed is similar. Because the relationship between peak rain and peak discharge is positive, the sediment yield increased as the peak discharge increased in B, C and D watersheds. The runoff characteristics of B watershed were similar to that of D watershed, but sediment yield characteristics of B watershed was the middle of that of A watershed and D watershed. Total sediment discharge decreased with vegetation recovery. The change of the sediment yield characteristics is found to be changed with vegetation recovery, but more time is required for runoff response recovery than the surface vegetation change.
Japan Society of Erosion Control Engineering