Study assesses use of erosion models for evaluation of stream crossing approaches

Sediment can be an important nonpoint source of water pollutants associated with forest operations if best management practices (BMPs) are not properly implemented. Excessive sedimentation can adversely affect water quality and aquatic ecosystems.

Stream crossings often require particular attention during forest harvesting operations to ensure that BMPs are appropriately applied and the potential for sediment delivery is minimized. However, the potential for sediment delivery from stream crossings is a complex issue governed by factors, including road attributes, soil composition, and infiltration characteristics.

As a result, forest managers sometimes use soil erosion and sediment delivery models to identify erosion-prone areas. Ranking erosion-prone areas with erosion models could inform management decisions about the need to apply additional or more appropriate BMPs.

Recently, scientists with Virginia Tech, with support from NCASI and others, conducted a study to (1) evaluate performance of five variations of three erosion models using field-informed measures by comparing model simulations to trapped sediment measurements, and (2) assess model utility for identifying stream crossing approaches that may require additional BMPs.

The three erosion models evaluated were the Universal Soil Loss Equation for forestry (USLE-Forest), Revised Universal Soil Loss Equation Version 2 (RUSLE2), and Water Erosion Prediction Project (WEPP). The five model variations were USLE-Roadway, USLE-Soil Survey, RUSLE2, WEPP-Default, and WEPP-Modified. Results from the models were compared to one year of trapped sediment data for 37 forest haul road stream crossings.

Based on their comparison, the authors concluded that “only WEPP-Modified estimates were not significantly different from trapped sediment data (p ≥ 0.107). While WEPP-Modified ranked best for most model performance metrics, the time, effort, modeling expertise, and uncertainty associated with model results may discourage the use of WEPP as a forest management tool. WEPP is better suited for researchers and government agencies that have the capability to measure extensive parameter data. Additional sensitivity analysis is needed to expand default parameters for forest roads within the WEPP and USLE models.”  

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 Reference 

Lang, A.J., W.M. Aust, M.C. Bolding, K.J. McGuire, E.B. Schilling. 2017. Comparing sediment trap data with erosion models for evaluation of forest haul road stream crossing approaches. Transactions of the American Society of Agricultural and Biological Engineers 60(2): 393-408. https://doi.org/10.13031/trans.11859