Comparison of Seepage Models Applied to Design of Trapezoidal Infiltration Trenches and Basins

In designing infiltration trenches or basins, the focus is usually on runoff conveyance and water quality, with less attention to optimizing infiltration and seepage to increase stormwater management efficiency. Four infiltration model conditions, applied as constituents of water balance in infiltration trenches and basins of a trapezoidal cross-section, were compared with the results of field studies. In the first two, infiltration rates conditions were constant and equal to native soil saturated hydraulic conductivity or to half of it along the side slopes. New analytical solutions for filling and emptying times based on the water balance equation were presented. The third model condition was a compilation of the inverse hodograph method with a simplified seepage function. The fourth model condition was based on Richards’ calculations solved numerically using the HYDRUS computer code. Among the analytical models, the authors recommend in-basin and trench designs using the concept IIIb. It predicts that the relative rate of infiltration from linear basins of trapezoidal cross-sections increases with the ratio of the water depth to the bottom width up to 0.8–2.4, depending on their side slopes. For higher relative water depth values, the relative infiltration rates stabilize, exceeding 20%–42% of the saturated hydraulic conductivity of the native soil. The relative infiltration rates from trenches or basins of trapezoidal cross-sections are less sensitive to the relative water depth than those from similar controls of a rectangular cross-section. Equations and procedures for the calculation of filling and emptying times are provided. The numerical model (HYDRUS 2D) gave satisfactory results, excluding the case of the filling of a trapezoidal trench without fill material.