Overland flow modeling in a vegetative filter considering non-planar topography and spatial variability of soil hydraulic properties and vegetation density

Vegetative filters are used to remove contaminants from overland flow. Little is known about the impacts of non-planar topography and spatially variable soil hydraulic properties and vegetation density on filter performance. In this study, we developed a protocol for modeling the effects of these quantities on overland flow features which influence greatly the filter efficiency. Two-dimensional overland flow was modeled using the physically based, distributed hydrologic model MIKE SHE. Soil hydraulic properties were represented using spatially variable saturated hydraulic conductivity and a spatially uniform soil–water retention curve. When field measured data and predictions from the uncalibrated model were compared, good agreement was found. The simulated volumetric outflow was within approximately 5% and 25% of the measured outflow at the two areas monitored within the study filter. Non-planar topography significantly impacted overland flow, but accounting for spatially variable roughness and variable soil hydraulic properties had a lesser impact on the two-dimensional overland flow. The volumetric outflow was affected by 36% and 20% because of non-planar topography, 14% and 18% due to variable roughness, and 15% and 16% because of variable soil hydraulic properties for the two grid areas, respectively.