Comparative Hydrologic Evaluation and Modeling of Two Field-Scale Infiltration Swales under Controlled Inflow Conditions

Abstract This study employs field-scale experiments and the storm water management model (SWMM) to analyze and simulate the hydrologic performance of two different infiltration swales: ALDOT infiltration swale (ALIS) and the modified infiltration swale (MIS), with a 0.3 m (12 in.) topsoil layer and a 0.15 m (6 in.) amended topsoil mix containing 20% pine bark fines, respectively, along with sand and gravel storage layers with different thicknesses. Two 1.5 m (5 ft) deep, same-size swales with 1% longitudinal slope were constructed using the two different engineered media designs. A total of 83 simulated infiltration tests were conducted over a 1-year period to validate and compare the infiltration performance of both swales under different operating conditions. The mean values of the average infiltration rates were 3.53 cm / h ( 1.39 in. / h ) for ALIS and 14.53 cm / h ( 5.72 in. / h ) for MIS, which is more than four times larger than ALIS, where topsoil limits it. The MIS consistently and statistically ( p = 0.003 ) drained faster and exhibited higher infiltration rates than ALIS, primarily due to its optimized media composition and improved vertical infiltration capacity. Both ALIS’s and MIS’s average infiltration rates increased by approximately 60% when the dry period was extended from 1 to 3 days, resulting in 15%–17% lower soil moisture. The SWMM bioretention module was used as an interpretive modeling tool for ALIS and MIS, which reproduced the average measured drawdown times well (root-mean-squared error of 0.19 h for 12 sets of experiments—52 tests) by calibrating soil saturated hydraulic conductivity and effectively simulated the swale’s surface infiltration, soil percolation dynamics, and subsurface storage behavior under different antecedent moisture and dry-period conditions.