Field Observation on Suspended Soil Runoff in A Sedimentation Tank

Abstract

Suspended soil runoff from agricultural basins has caused sea water pollution in coral and island ecosystems in Okinawa, so suspended soil runoff management is required for the conservation of the sea environment The purpose of this study was to research suspended soil runoff in a sedimentation tank. For the purpose of this study, field observation was conducted using a real sedimentation tank for many rainfall events. Discharge and water sampling during a rainfall event were observed, and suspended soil concentration and suspended soil grading were analyzed. From the observed results, soil balance in the sedimentation tank, trap efficiency, and the inflow-capacity ratio were calculated. In conclusion, the results indicate that a part of input fine soil (<75μm) passes the sedimentation tank. The inflow-capacity ratio is also found to be an essential parameter useful to estimate trap efficiency of suspended soil in a sedimentation tank.