Improving salt leaching efficiency of subsurface drainage systems using low-permeability surface mulch

Surface ponding is often used in combination with subsurface drainage systems to leach excessive salts from the saline soils of reclaimed coastal areas. However, soils that are not immediately proximal to subsurface drains are typically subjected to reduced leaching efficiency (LE). This study evaluates an approach for increasing the LE through the use of a low-permeability surface mulch (LPSM) above the drain. Sand tank experiments and 2D numerical simulations were conducted to examine the effectiveness of LPSM configurations under continuous surface flooding. The results show that the addition of a LPSM leads to more spatially uniform, accelerated salt leaching towards subsurface drains. As a result, base case leaching periods and freshwater application rates were reduced by up to ∼60% and ∼80%, respectively. The sensitivity analysis based on field-scale models revealed optimal values (i.e., leading to maximum LE) of the LPSM hydraulic conductivity and length. Moreover, an approximate method is applied to estimate the leaching period, and to thereby assist in the design of drainage-LPSM schemes. We conclude that the addition of a LPSM is an effective strategy to enhance salt leaching under surface ponding, adding to existing methods for ameliorating saline soils.