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Evaluation of WEPP for runoff and sediment yield prediction on natural gas well sites

Wachal, D.J., Harmel, R.D., Banks, K.E., Hudak, P.F.
Transactions of the ASABE 2008 v.51 no.6 pp. 1977
Water Erosion Prediction Project, disturbed soils, runoff, sediment yield, prediction, water erosion, stormwater, Texas
Natural gas exploration and production requires land-disturbing construction activities that have the potential to accelerate soil loss due to land cover modifications, increased slopes, and flow concentration. In the U.S., nearly 30,000 new gas wells are drilled each year. Erosion modeling has been successfully used for decades to predict soil loss and conservation effects on agricultural fields, rangelands, and forests, although much less research has been conducted on the application of erosion models for disturbed construction site conditions. The objective of this research was to evaluate Water Erosion Prediction Project (WEPP) runoff and sediment yield predictions relative to measured data from two natural gas well sites (referred to as GW1 and GW2) in north central Texas. Model parameters were adjusted from WEPP default parameters based on available literature and model observations. A low effective hydraulic conductivity value (0.75 mm h-1) resulted in successful runoff predictions. Agreement between predicted and measured sediment yields was accomplished by increasing rill and interrill erodibility values and decreasing critical shear stress values from default values. WEPP performance was evaluated with the Nash-Sutcliffe efficiency (NSE), root mean square error (RMSE)-observation standard deviation ratio (RSR), and percent bias (PBIAS), as well as modified versions of NSE and RSR that consider uncertainty in measured validation data. For GW1, NSE and RSR evaluation of WEPP performance was considered "good" for runoff (NSE = 0.68 and RSR = 0.56) and "satisfactory" for sediment yield (NSE = 0.63 and RSR = 0.61). For GW2, NSE and RSR values were "very good" for runoff (NSE = 0.76 and RSR = 0.49) but "unsatisfactory" for sediment yield (NSE = 0.32 and RSR = 0.83). Use of modified NSE and RSR to consider measurement uncertainty improved model performance to "very good" for all instances. PBIAS values were relatively low and considered "very good" for GW1 and GW2 runoff and sediment yield predictions. These results demonstrate that WEPP can effectively model runoff and sediment yields from natural gas well sites, thus making it a useful tool for evaluating potential sediment impacts and management alternatives to minimize sediment yields from natural gas well sites.