Abstract
Shikoku island has several major tectonic lines, such as the Median tectonic line, the Mikabu tectonic line and the Butsuzo tectonic line. Influenced by the tectonic lines, the bedrocks in the Shikoku mountainous region are often weak. This causes frequent fracture-zone landslides and collapses in the area.
On the other hand, as the notion that the sediment issue in a watershed should be dealt collectively from the headwater area to the coastal drift sand area is proposed recently, we studied the actual condition of the sediment yield in the Shikoku mountainous region by the sedimentation in the reservoir of the dams and the erosion control dams to discuss about the new Sabo project plans.
Consequently, the average specific annual sediment yield in Shikoku mountainous region is estimated as 0.59 × 103 (m3/km2/year), and the value of the produced unstable sediment at the disaster time is sometimes accumulated ten times as much as usual time.
And we pointed out one of the most serious sedimentation problems in the reservoir is the consumption of its effective storage capacity.
