Mathematical simulation for flood inundation and gate operation of a main drainage canal in a flat low-lying agricultural area

Chiyoda basin is located in Saga Prefecture in Kyushu Island, Japan, and lies next to the tidal compartment of the Chikugo River to which the excess water in the basin is drained away. Chiyoda basin has a total basin area of about 1,100 ha and is a typical flat and low-lying paddy-cultivated area. The main problem in this basin is the inundation analysis and prediction of the potential inundation in term of total inundation time, total inundation area, the coeficient of variances of maximum inundation depth in paddy tanks and the maximum inundation depth in paddy tanks. This paper presents a mathematical model of a drainage system in Chiyoda basin for calculating the flood inundation and predicting the potential inundation. First, the algorithm of gate operation was simulated and the drainage model was then evaluated by comparing the simulated water levels with observed ones during an actual rainfall event. The results show that the observed and simulated water levels are in good agreement, indicating that the proposed model is applicable for drainage and inundation analyses in flat low-lying paddy-cultivated areas. Second, the potential of inundation was predicted using a stochastic rainfall time series with a return period of 30 years and the tidal conditions of spring and neap tides in Chikugo River. The parameters of this inundation scenario such as a total inundation time, a total inundation area, a coefficient of maximum inundation depth in paddy tanks and maximum inundation depth in paddy tank were ditermined. For further, this model will be able to provide managers and operators a usefull tool that is to optimize the gate operation in order to minimize the damages for crop and store the water for the irrigation purposes.