2012 Volume 80 Issue 2 Pages 117-124
This study aims to investigate changes in runoff characteristics due to the increase of abandoned terrace paddies in hilly areas. To do so, 3 experimental watersheds were selected based on land use and cultivation status of paddies: namely Cultivated Paddy-dominant Watershed, Abandoned Paddy-dominant Watershed and Forest Watershed, whose areas are approximately 1km2. The retention capacity, runoff ratio and peak runoff coefficients for large discharges from each watershed were analyzed using rainfall and discharge data observed at 10-minute intervals. First, it was determined that the peak runoff coefficients of the Cultivated and Abandoned Paddy-dominant Watersheds were 0.24 and 0.30, respectively. In addition, the runoff ratios of the Abandoned Paddy-dominant Watershed were, under wet conditions, found to be 31.4% higher than those of the Cultivated Paddy-dominant Watershed at the maximum. These results indicate that abandonment of paddies lead to larger peak discharges and direct runoff, suggesting a higher flood risk in the area. Meanwhile, the maximum retention capacity of the Abandoned Paddy-dominant Watershed decreased by approximately 10mm compared with those of the Cultivated Paddy-dominant and Forest Watersheds, suggesting lower water availability in dry periods.