Difference of the sediment yield characteristics with vegetation recovery
in granite watershed
Tetsushi ITOKAZU, Yuichi ONDA, Takeshi OHTA, Hiroaki SUGIMORI and Hirofumi
SHIBANO
Abstract
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.