Impact of Wetland Resolution on Hydraulic and Contaminant Transport Predictions

Accurate assessment of wetland hydraulic performance and solute treatment depends on the spatial resolution of bed topography and vegetation density. To evaluate this influence, synthetic shallow-water wetlands with spatially correlated random fields of bed elevation and vegetation density were used to examine how data resolution affects predictions of hydrodynamic residence time and treatment performance. Coarse-graining of input data produced modest median errors in nominal residence time, although variability across realizations increased with greater topographic heterogeneity. The variance of residence time was the most sensitive metric, showing a consistent tendency toward underestimation as grid size increased, with maximum median errors exceeding 10% and 35% for grid sizes equal to and twice the correlation length, respectively. In contrast, outlet concentration errors remained relatively small, typically below 5% even when grid size exceeded the correlation length of bed features, indicating a stronger dependence on nominal residence time than on variance. Within the range of vegetation stem density variability considered, heterogeneous vegetation patterns in a flat-bed wetland exerted comparatively little influence on residence time metrics and contaminant concentration at the outlet. The results provide insights into the reliability of wetland models under varying data resolutions and identify conditions under which coarse-graining is acceptable, offering guidance for field measurement strategies and numerical modeling.