石垣島名蔵川流域における土砂流出に関するGISの構築と現地観測

抄録

In Okinawa, red-soil runoff becomes a remarkable problem, and polluted water destruct ecosystem. In consideration of soil erosion mechanisms (rainfall impact, overland flow), watershed GIS was constructed using land use, length and slope. Field observation was performed to grasp the properties of sediment runoff. Turbidity, discharge and precipitation and SS concentration were measured in Nagura watershed. From the field observation, amount of sediment runoff was 98.2ton from whole watershed. The relation between information in watershed and sediment discharge has shown that summer sugarcane and pine fields with steep slope are the main source of sediment yield. In order to reduce sediment runoff, sugarcane farming method should be shifted from summer type to spring type or perennial type and steep slopes should be gentle ones.