Watershed and streambank erosion modeling in a coldwater stream using the GWLF-E model: application and evaluation

Abstract

While many watershed models estimate overland flow-related soil loss, streambank erosion is often overlooked even though it can be the dominant source of sediment in a catchment. We used the enhanced generalized watershed loading functions (GWLF-E) model to simulate the water budget, field erosion from the landscape, and streambank erosion along a gradient of agricultural to urban land cover from 1997 to 2015 in the Indian Mill Creek watershed of Michigan, USA. We evaluated discharge simulations using in-streamflow measurements and evaluated streambank erosion simulations using field-collected erosion pin measurements from a previous study. Annual water budget results suggest the creek is primarily groundwater fed, but that a per-subbasin average of 6–15% of precipitation becomes runoff. Field erosion contributed a per-subbasin average of 0.5–2.5 Mg ha−1 year−1 of sediment, while streambank erosion accounted for 0.2–50.1% of the subbasins’ total sediment yields. Average lateral erosion rate of streambanks in subbasins ranged from 0.04 to 7.37 cm year−1, with four subbasins exceeding 1.0 cm year−1. Evaluation with field-collected discharge data suggest that GWLF-E may have been overestimating discharge in the subbasins. Evaluation with streambank erosion data found that GWLF-E may have difficulty capturing the complexity of erosion rates, including instances where sediment is deposited on streambanks from upstream sources, and that it underestimates streambank erosion in headwater catchments sometimes over an order of magnitude. Our findings are important for watershed managers to evaluate modeling approaches and highlight the importance of modeling both field and streambank erosion.