PREDICTIVE EVALUATION OF RUNOFF CONTROL EFFECT OF THE INTRODUCTION OF PADDY FIELD DAM IN THE KURO RIVER BASIN OF THE SHIRA RIVER SYSTEM

Abstract

 In this study, we estimated the effect of the introduction of a paddy field dam with different functions on the reduction of the runoff and inundation into the main river and characteristics of runoff control in each paddy field district in the Kuro River basin of the Shira River system in the Kumamoto Prefecture. The results showed that the introduction of the paddy field dam that covers 1687 ha of the paddy field produces the highest reduction in the runoff to the main river through a 50-mm outlet hole for the 10-, 30-, and 50-year probabilities of rainfall; it reduces the peak flow by 33.7 m³/s (5%) and inundation area by 54 ha（7.1%）for the 50-year probability of rainfall. Furthermore, the peak cutoff per hectare to the downstream of each paddy field district was estimated to be higher when the topographic gradient is larger and there is no backwater.