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 the RRD is markedly flat, and 56% of the central part is less than 2 m above sea level. In the flat low-lying area of the RRD, many pumping stations for irrigation and drainage have been constructed as a result of the government's adoption of the Doi Moi (renovation) policy in 1986. Most 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 mathematical 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-cultivated area in the RRD. This model was developed from a flat low-lying area tank model to identify potential problems in the further 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 inundation occurred in the paddy fields apart from the pumping 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 culverts; complicated drainage networks; and extremely flat topography. The results also suggested that in the further study the following information should be collected through field surveys, including interviews with farmers: accurate drainage network and topographic data, accurate capacity and arrangement of pumping machines, actual operation of pumping machines, rainfall time series data at one-hour intervals or shorter, and actual situations of inundation during past floods.