Modeling Field-Scale Bioretention Cells with Heterogeneous Infiltration Media

Abstract

To address increasing stormwater management concerns in metropolitan and suburban areas, bioretention systems are a mitigation technology that helps address both water quantity and quality. However, it is critical for stormwater managers and engineers to model the hydraulic performance of these systems before investing in the infrastructure. This means an appropriate model must be selected to efficiently reflect important aspects of the given site and design. This work investigated the ability of a one-dimensional model to simulate water movement through a heterogeneous bioretention cell. For model validation, two full-size bioretention cells in Grove, Oklahoma, were flooded a total of three times, and parameters related to overflow, drainage and relative change in soil moisture were measured. Observed values were compared to predictions using an uncalibrated model previously developed and run with area-weighted soil parameters (“original model”). In addition, observations were compared to an uncalibrated “revised model,” which allowed modeling of distinct infiltration media. The revised model allowed for two separate soil types in the horizontal plane and simulated maximum subsurface drainage flow rate (23.6% to 33.7% from observed), volume (7.9% to 38.9% from observed), and timing (14.7% to 92.5% from observed) better than the original model, but the original model generally simulated overflow volume (12.2% to 77.1% from observed) and peak overflow rate (3.6% to 9.6% from observed) more closely. It was concluded that the revised model was more appropriate for modeling heterogeneous systems when concerns exist about timing of hydrographs and all underdrain parameters.