Drainage Work on the Settling Basin to Prevent Red Soil Outflow and the Natural Drying of the Deposited Red Soil

Abstract

In Okinawa Prefecture a problem concerning the outflow of red soil has surfaced whereby red soil flowing out from farmlands is deposited in settling basins. The current concern is to prevent this deposited red soil from flowing out of the basins. In treating this deposited red soil, it is necessary to take into consideration the creation of a recycling-based society and the effective use of local resources from the viewpoint of social technology. In a pilot area in the main island of Okinawa, a drainage test was conducted and the natural drying of the deposited red soil was simulated using technologies based on farmland engineering and hydraulics. The objective of this test was to study a red soil recycling system for the reuse and restoration of the deposited red soil. In the drainage test conducted using an underdrain within the settling basin, water could be drained out of the pilot area without high turbidity. A drying test conducted after the drainage demonstrated that a deposit 10 cm deep required 2.5-6 days for effective drying if the daily evaporation was 3-7 mm. The most appropriate period for the drainage and drying of the deposit was October to November, if the weather conditions and work environment of this region were taken into consideration.