A Hydrologic Analysis on Inundation in the Flooding Area of the Mekong Delta, Cambodia: The Combined Deterministic and Stochastic Models for Flood Forecasting

Since the watershed of the Mekong River is situated under the typical monsoon climate, the Mekong River presents a distinct variation in its water levels between the dry and rainy seasons, and causes heavy inundation in the Delta area along the river every year. In order to analyze the flow phenomena and inundation process for agricultural practice in the Mekong Delta, this study tried to establish three models: the combine of "3*4+1-type" model and the ARMA time series model, Tonle Sap Lake Storage Model and Delta Water Balance Model. The "3*4+1-type" Model was employed to calculate the runoff of the Lower Mekong River Basin from Chiang Saen to Kompong Cham and its sub catchments. The ARMA time series model was applied to the residuals of the Tank Model application in order to obtain 1 day to 5 days ahead flow forecasting after the present day based on the available data of the present day. The inflow to the Tonle Sap Lake was also estimated by the "3*4+1-type" Model, whereas outflow of the lake was formulated based on the relationship between storage volumes and water level of the Lake surface. The application of the ARMA to the "3*4+1-type" model was found effective to improve flood forecasting at the outlets point of each sub-catchment. The established storage model for the Tonle Sap Lake could calculate well for simulating the outflow and the seasonal water balance of the Tonle Sap area. Deltaic area was divided into four zones, and water balance of each zone was formulated by considering the zone's inflow/outflow between rivers and flooding areas. The establishment of these three models could provide a basic framework for modeling the Mekong Delta, Cambodia.