Drainage and Inundation Analysis in a Flat Low-lying Paddy-cultivated Area of the Red River Delta,Viet Nam

The Red River Delta (RRD) is located in the northern Viet Nam. The central part of RRD is markedly flat, and 56% of the central part is less than 2m above sea level. In the flat low-lying area of the RRD, many pumping stations for irrigation and darainage have been constructed as a result of the goveanment\u27s adoption of the Doi Moi (renovation) policy in 1986. NMost of the excess water in the rainy season is now removed by pumped drainage. However, inundation still occurs in paddy fields, damaging summer rice cultivated in the rainy season. This paper presents a mathmatical model of drainage system for calculating inundation and excess water removal during the rainy season in Phu Lam Commune, which is a typical flat low-lying paddy-culticated area in the RRD. This model was developed from a flat low-lying area tank model to identify potential problems in the futher development of the drainage system. The present situation of excess water removal and inundation was then evaluated by numerical simulations using the model. The results indicated that the inindation occured in the paddy fields apart from the pamping stations. Also considered was the low flowing capacity of drainage facilities between the first and the second canals, resulting from inadequate maintenance of drainage facilities such as sluggish, weedy canals and cultiverts; complicated drainage networks; and extremely flat topography. The results alsp suggested that in the further study the following information should be collected through fields surveys, including interviews with framers: accurate drainage network and topographic data, accurate capacity and arrangement of pumping machines, actual operation of pumping machines, rainful time series data at one-hour intervals or shorter, and actual situations of inundation during past floods