| Summary: | An area of about 300,000 acres in Dinajpur and Rangpur districts will be irrigated by the combination of pumpage from the Tangon and Karatoa rivers and from about 1000 wells located between the rivers. It was calculated that the lowering of the water table 12-15 feet, as needed for irrigation, due to pumpage from the underground will stop or severely limit the accretion to the stream flow from underground. The Tangon will, in absence of accretion to the stream from the underground, cease to flow during the irrigation season. Likewise the flow of Karatoa, in absence of accretion to the stream from the underground will be reduced to about 153 cfs which can be used to irrigate 15,000 acres along the banks of rivers only. The average discharge of 2.5 cfs over a 150-day interval of wells located 3000 feet apart will not exceed the average annual recharge of 2.8 feet to the aquifer from precipitation. This particular arrangement was examined from the relationship of aquifer characteristics - transmissivity 120,000 gpd/ft and the storage coefficient 0.20. The resulting calculated benefit-cost ratio of the benefit of crops produced from assured irrigation to the cost of construction of wells 275 feet deep is 2:1. If the average aquifer properties remain constant at depths greater than 275 feet, better economy will result by drilling wells deeper than 275 feet.
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