Assessment of groundwater recharge from paddy fields in the selected delta of the Indian Sundarbans

Groundwater recharge from the paddy field grown under rainfed conditions in the Indian Sundarbans delta was assessed using the HYDRUS-1D model. Ponding depth in the paddy field during the simulation period was maintained at 10 cm. Throughout the entire cultivation period of the paddy in the region, simulations were conducted to assess recharge flux, root water uptake, evaporation, and surface runoff. The total rainfall during the simulation period was 64.04 cm. The paddy field exhibited a cumulative bottom flux of 13.61 cm. Additionally, the cumulative measurements for surface runoff, evaporation, and actual root water uptake were 2.77 cm, 13.19 cm, and 11.57 cm, respectively. The very low cumulative surface runoff was due to the bund height being 30 cm, which is very common in the study area, and surface runoff takes place when rainfall exceeds the bund height. Low cumulative bottom flux was due to very low saturated hydraulic conductivity, which is a typical characteristic of silty clay loam soil in the deltaic region.