EVALUATING THE FUNCTION OF SOIL EROSION PREVENTION ON FARMLAND BASED ON SATELLITE IMAGES AND GIS DATABASE: CASE STUDY OF ALL FARMLANDS ON OKAYAMA PREFECTURE, JAPAN

摘要

Agriculture activity has not only to product crops but also to have multi functionality like the function of soil erosion prevention. This paper evaluates the function of soil erosion prevention in Okayama Prefecture which has many hilly and mountainous areas. This function is related to soil erosion, we apply the USLE (Universal Soil Loss Equation) to evaluate. Evaluated area is wide about 80 km × 100 km, we estimate the function based on GIS datasets. At first, we estimate soil erosion in present farm land conditions. Present farmland condition is determined from GIS and satellite images. Coefficients of USLE are determined from AMeDAS datasets, soil maps, DEM, aerial photographs, related reports of soil erosion and ground survey. Next, we assume the future scenario that paddy fields in hilly and mountainous area would be abandoned and be changed to natural landforms. We estimate soil erosion in this future scenario. We defined the function of soil erosion prevention is the differences of present soil erosion and future scenario. As a result, soil erosion of paddy field in hilly and mountainous area would increase from 1.4 to 37.7 t/ha/yr. The farmers contract paddy fields in flat and levees are covered with vegetation. It is obvious that agricultural activity conserved the farmlands. This method has good advantage for evaluating the function of soil erosion prevention in wide area and applies to many cases of scenarios.