Abstract
Irrigation and to assess groundwater quality and availability in the study area for irrigation. As the rainfall was not uniformly distributed throughout the year, the Boro rice was fully dependent on irrigation water. From field experiments it was found that about 50% of the irrigation water is needed for evapotranspiration (ET) and the rest 50% is lost through seepage and percolation (S&P) annually from double cropped rice fields. The study indicated that continuous standing water in rice field was not necessary for optimum yield. Moreover, without sacrificing much yield about 27% of valuable irrigation water can be saved over continuous standing water condition by practicing the recommended method of irrigating rice field after 3 days of disappearing standing water. This method required 747 mm of water in Boro season and gave the highest water productivity (0.67 Kg/m³ of water). This method also gave the highest net benefit of Tk 1207 per ha over continuous standing water method. It was found that rice can be grown successfully with negligible yield loss if the soil moisture content is depleted up to 75 – 80% of saturation. Therefore, it was concluded that irrigating rice field after 3 days of disappearing of standing water was the best method for farmers managed irrigation project area in respect of yield, water requirement and economic return. In the Barind confined aquifer, the value of transmissivity (T) and storage coefficient (S) ranged from 843 to 4168 m²/day and 7.96 x 10⁻⁴ to 5.26 x 10⁻³ respectively. The groundwater table was found gradually declining day by day during dry season due to increasing demand for abstraction but the aquifer was found to be fully recharged after the monsoon. The annual recharge ranged from 359 mm (Sapahar area) to 663 mm (Godagari area) which was about 30 - 58% of the rainfall during recharging period. Based on additional available groundwater, minimum 2% ( Nachole area) and maximum 14% (Paba area) of the land area in the selected thanas could be brought under irrigation. At present about 80% of the available groundwater is being used and the rest 20% is available for future use. The results of chemical analysis showed that the pumped groundwater is suitable for irrigation purposes in the Barind area.