Journal of the Japan Society of Erosion Control Engineering, Vol.58,No.3,2005
Factors affecting vegetative invasion of the sediment trap area of sabo
dams
in the Mogami River basin using aerial photograph
Takashi KOI Norifumi HOTTA Masakazu SUZUKI
Abstract
Although many sabo dams have been constructed in mountainous riparian zones, few
studies have examined the subsequent transition of riparian vegetation as a result
of sediment deposition. In the future, the maintenance of sabo dams and their
sediment trap areas must consider the effects of invading vegetation on the river
environment, while ensuring the dams' disaster]prevention function. This study
investigated the long]term vegetative invasion of sediment trap areas following
the construction of sabo dams from time]series aerial photographs, and examined
related factors. The study sites were the sediment trap areas of 27 sabo dams
in the Mogami River basin, in Yamagata Prefecture, Japan. We found that vegetation
invaded the sediment trap areas of 23 of the sabo dams. The vegetation invasion
could be classified into six types, according to the timing of invasion or the
dynamics following invasion. type]A had no vegetation invasion because of impounded
water; type]B had vegetation invasion before the dam pocket was filled; type]C1
had vegetation invasion as soon as the dam pocket was filled; type]C2 had lost
the invading vegetation; type]C3 took several years for the vegetation invasion
after the dam pocket was filled; and type]D had no vegetation invasion because
of constant sediment transport. These invasion types clearly corresponded to the
number of years since the dam pocket was filled (Y). The degree of sediment transport,
which affects the ability of vegetation to invade the sediment trap area, is a
function of the sediment trap capacity (V) and average annual sedimentation volume(Qd)(or
V, watershed area (A) and average specific annual sedimentation volume (Qd–)).
These factors result in the vegetation invasion having the same value of Y.
Key words:Cs]137, sabo dam, sediment trap area, vegetation invasion, aerial photograph
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