18 巻 (2012) 2 号 p. 17-27
Makabe, which is located in the southern-most part of the main Okinawa Island, is an upland agricultural area that produces sugarcane and vegetables. Geographic features in Makabe-South have created a flood-prone basin that make it one of the most flood-damaged areas in Okinawa. For example, in August 2007 a heavy rainfall event resulted in flood damage over an area of 20 ha. Several measures have been proposed to help mitigate flood damage in this region, which features a relatively complex drainage system. To evaluate and compare these proposed measures, it is important to understand the infiltration mechanisms at work in the area. We use a surface runoff model to compute rainfall outflow for our study site. To simulate the study site's complex infiltration and drainage system, we model two adjacent infiltration ponds with different infiltration capabilities. Among other factors, infiltration rates depend on overflow between these two adjacent ponds, which occurs through both a subterranean and pipe flow drainage system. The simulation results indicate that our modeling approach is useful for evaluating the flood mitigation measures proposed in this region.