[A-HW24] 流域圏生態系における物質輸送と循環：源流から沿岸海域まで

[AHW24-12] 沖縄島北部の沈砂池における土砂生産と堆砂速度

*廣瀬 孝¹、仲宗根 健太²、川島 滋和³、小野寺 真一⁴、齋藤 光代⁵ (1.国立大学法人　琉球大学、2.大同火災海上保険株式会社、3.宮城大学、4.広島大学大学院先進理工系科学研究科、5.岡山大学 大学院環境生命科学研究科)

キーワード：赤土流出、沈砂池、沖縄島、土砂生産、裸地

Red soil erosion is one of the environmental problems of the Ryukyu Islands. Coral reefs have been received damage and fishery has been affected by soil flowing out into the sea. Red soil erosion in late years happens mainly by farmland. The settling basin is one of the prevention measures for red soil erosion. The settling basin traps sediment before going out to outside the area and reduces sediment outflow to outside, and constant capacity is necessary for covering area. It is necessary to restore capacity by dredging for function maintenance that settling basin capacity decreases because the red soil which began to flow deposits and makes functional decline. It is necessary to know sediment yield and sedimentation rate in the settling basin to do effective operation.
In this study, thickness of sediment is measured in 14 settling basins with different setting times in the northern part of Okinawa Island, and sedimentation rate and denudation rate are estimated.
The results of these investigations are as follows:1) It takes 8-25 years to deposit about 80% of capacity of the settling basin. 2) The denudation rate is 0.03-0.17cm/year (300-1,700mm/1,000 years). 3) The bare land area in the covering area of settling basin have very good relationships with Sediment yield and sedimentation rate.