Abstract
AbstractPhysically based models are useful frameworks for testing intervention strategies designed to reduce elevated sediment loads in agricultural catchments. Evaluating the success of these strategies depends on model accuracy, generally established by a calibration and evaluation process. In this contribution, the physically based SHETRAN model was assessed in two similar U.K. agricultural catchments. The model was calibrated on the Blackwater catchment (18 km2) and evaluated in the adjacent Kit Brook catchment (22 km2) using 4 years of 15 min discharge and suspended sediment flux data. Model sensitivity to changes in single and multiple combinations of parameters and sensitivity to changes in digital elevation model resolution were assessed. Model flow performance was reasonably accurate with a Nash–Sutcliffe efficiency coefficient of 0.78 in Blackwater and 0.60 in Kit Brook. In terms of event prediction, the mean of the absolute percentage of difference (μAbsdiff) between measured and simulated flow volume (Qv), peak discharge (Qp), sediment yield (Sy), and peak sediment flux (Sp) showed larger values in Kit Brook (48% [Qv], 66% [Qp], 298% [Sy], and 438% [Sp]) compared with the Blackwater catchment (30% [Qv], 41% [Qp], 106% [Sy], and 86% [Sp]). Results indicate that SHETRAN can produce reasonable flow prediction but performs less well in estimation of sediment flux, despite reasonably similar hydrosedimentary behaviour between catchments. The sensitivity index showed flow volume sensitive to saturated hydraulic conductivity and peak discharge to the Strickler coefficient; sediment yield was sensitive to the overland flow erodibility coefficient and peak sediment flux to raindrop/leaf soil erodibility coefficient. The multiparameter sensitivity analysis showed that different combinations of parameters produced similar model responses. Model sensitivity to grid resolution presented similar flow volumes for different digital elevation model resolutions, whereas event peak and duration (for both flow and sediment flux) were highly sensitive to changes in grid size.
Highlights
Surface flow and soil erosion are natural processes affected by changes in agricultural land use and management in catchments
Continuous flow and suspended sediment data from two nearby agricultural catchments in the United Kingdom were used for model calibration and evaluation, with the assessment of model efficiency focussing on flow volume, peak discharge, sediment yield, peak sediment flux, and event duration for a range of digital elevation model (DEM) grid sizes
The proxy-catchment test in this study showed better performance in the calibrated catchment (Blackwater) than the evaluated catchment (Kit Brook) probably due to a higher soil permeability in Kit Brook than Blackwater (Figure 2)
Summary
Surface flow and soil erosion are natural processes affected by changes in agricultural land use and management in catchments. Studies that adopt this model testing approach in combination with high-resolution measurements of discharge and sediment flux were not found in the available literature Another common criticism of PBSD model is grid size applications (Beven, 1991; Brazier et al, 2011), as parameter values applied to a catchment grid are usually an average of a physical property (measured or calibrated). This generalization fails to capture natural variability in a given property and may affect hydrological process representation (Thomas et al, 2016). Continuous flow and suspended sediment data from two nearby agricultural catchments in the United Kingdom were used for model calibration and evaluation, with the assessment of model efficiency focussing on flow volume, peak discharge, sediment yield, peak sediment flux, and event duration (flow and sediment) for a range of DEM grid sizes
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