Abstract
From the viewpoint of watershed management, paddy areas are regarded as having important functions beyond their role in food production; these include flood regulation, fostering of water resources, and prevention of soil erosion. These functions are commonly found in low-lying paddy areas such as in Japan, Cambodia, Vietnam, and other countries, where the levels of development of paddy irrigation are quite different. In this study, a flood inundation model, which covers floodplains of the Mekong River from Kratie in Cambodia to near the Vietnamese border, was developed by using the FEM technique with 2-D shallow water equations. The model was applied to the water flows over the years 1996 through 2003. Main roads, dikes, colmatages, and waterway-opening works in the study area, which enable water to be stored, were taken into account in the simulation. The flood regulation function of paddy fields in the study area was then assessed, using the results of the model simulation and land-use data. Namely, the volume of flooded water on paddies was estimated in order to evaluate the impact of flood storage by paddies on floods and water use. The results showed that about one-fifth of the total flood volume is stored on paddies in and around Tonle Sap Lake, and rice cultivation starting after the flood waters recede.
