Brief summary of the hydrogeology of Bangladesh

The average annual precipitation in Bangladesh ranges from about 50 inches in the west-central part to about 200 inches in the northeast. Most of the rain falls during the southwest monsoon so that local precipitation is heavy at the same time flood waters of the Brahmaputra and Ganges rivers arrive. The result is that most years about 50 percent of Bangladesh is inundated; in very wet years inundation may exceed 70 percent of the total land area. Consequently, over much of the country the annual recharge to the ground-water reservoir is large. Annual fluctuations of the ground-water level are commonly about 10 feet in the northern part of the country. If a storage coefficient of 0.2 is assumed, annual recharge may be about 24 inches of water. Although the amount of recharge is different from area to area, it is almost everywhere very substantial in the Ganges-Brahmaputra Delta.