Field and numerical evaluation of discontinuous improved subsurface drainage for waterlogging control

Due to the shortage of farmland, subsurface drainage systems are progressively replacing the lowest-level open ditches, representing an emerging trend in water management practices in China. While subsurface drainage systems are engineered to remove waterlogging, their efficacy in resolving surface ponding is fundamentally constrained by soil permeability. To address this issue, a discontinuous improved subsurface drainage (DISD) has been proposed, featuring discontinuous filter extending from the pipe to the soil surface. Field and numerical experiments have been conducted to evaluate the performance of this proposed system on waterlogging removal and groundwater control. Based on a calibrated and validated HYDRUS-3D model, the simulations involved variations in filter heights, filter widths, filter spacings, and drain spacings have been conducted. The results indicated that DISD exhibited superior performance under conditions of surface ponding and short-duration heavy rainfall, enhanced efficiency in lowering the groundwater table compared to CSD (conventional subsurface drainage) for shallow groundwater table situation. Field experiments revealed that the cumulative discharge of DISD was approximately 2–2.3 times higher than CSD for short-term drainage and 1.37 times higher for long-term drainage. Numerical simulations showed that with a sand-gravel filter length ranging from 0.2 m to 4 m and a filter width of 1.2 m, the drainage discharge of the DISD was 1.91–5.40 times of CSD when surface ponding occurred. DISD is outperformed than ISD (improved subsurface drainage) in removing surface waterlogging when the filter volume of DISD is more than 6 % of ISD. DISD also does better in subsurface waterlogging control than ISD. These research findings provide a scientific basis for designing DISD and lay a solid foundation for their broader application in China.