Shallow subsurface drainage for managing seasonal flooding in Ganges floodplain, Bangladesh

The impact of shallow subsurface drainage was investigated as a pilot study on a 0.13 ha plot of a farmer’s field located in Batiaghata, Khulna District, Bangladesh, in the floodplain of the Bay of Bengal. The drainage design differed from traditional subsurface tile drains in two respects: (i) the depth of drains was shallow (30 cm); and (ii) the design did not include a sump and accessories such as pumps (drainage outlets were tidal). A monsoonal paddy rice crop followed by a winter sunflower crop was evaluated. The experimental treatment was a shallow subsurface drainage system with a drain depth of 0.3 m and drain spacing of 8 m. Measurements of surface flooding depth and groundwater table depth were made weekly and subsurface drainage discharge during managed drainage of the field was measured to determine system responsiveness. The managed subsurface drainage enabled the establishment of the winter sunflower crop 1.5 months earlier than the usual local practice, increased the yield and facilitated safe harvest, avoiding pre-monsoonal rainfall damage. Farmers expressed increased interest in managed subsurface drainage for its potential for early establishment of rabi crops and increased yields in the study area. This study outlines the potential benefits resulting from subsurface drainage in Khulna District.