Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2008
Publication Date: 2/20/2009
Citation: Dun, S., Wu, J.Q., Elliot, W.J., Robichaud, P.R., Flanagan, D.C., Frankenberger, J.R., Brown, R.E., Xu, A.C. 2009. Adapting the Water Erosion Prediction Project (WEPP) Model for Forest Applications. Journal of Hydrology. 366(2009):46-54. Interpretive Summary: Soil erosion is a natural hazard that can reduce the productivity of soils, as well as produce sediment that can pollute streams and endanger fish spawning areas. In order to estimate how much erosion occurs at a particular location due to climate, soil, slope and management activities, computer simulation models have been developed. This paper describes improvements that have been made to the Water Erosion Prediction Project (WEPP) model, so that it does a better job of predicting the plant growth and amount of runoff and soil loss from forested areas. Forests have substantially different physical processes that affect how much water moves over the surface of the soil, and laterally below the surface of the soil. The changes to the WEPP model were tested with data from a small forested watershed in Idaho, and the results showed that the new model version does a much better job of simulating the hydrology in the forest there. This research impacts USDA-Forest Service staff, NRCS foresters, BLM staff, other federal, state and local agency personnel, and others involved in environmental assessment of runoff and sediment generation from forested areas. Improvement of the ability to model hydrology and erosion processes in forests will allow for better management and more appropriate mitigation strategies to reduce on-site and off-site damages due to timber harvesting and wildfires.
Technical Abstract: There has been an increasing public concern over forest stream pollution by excessive sedimentation due to natural or human disturbances. Adequate erosion simulation tools are needed for sound management of forest resources. The Water Erosion Prediction Project (WEPP) watershed model has proved useful in forest applications where Hortonian flow is the major form of runoff, such as modeling erosion from roads, harvested units, and burned areas by wildfire or prescribed fire. Nevertheless, when used for modeling water flow and sediment discharge from natural forest watersheds where subsurface flow is dominant, WEPP (v2004.7) underestimates these quantities, in particular, the water flow at the watershed outlet. The main goal of this study was to improve the WEPP v2004.7 so that it can be applied to adequately simulate forest watershed hydrology and erosion. The specific objectives were to modify WEPP v2004.7 algorithms and subroutines that improperly represent forest subsurface hydrologic processes; and, to assess the performance of the modified model by applying it to a research forest watershed in the Pacific Northwest, USA. Changes were made in WEPP v2004.7 to better model percolation of soil water and subsurface lateral flow. The modified model, WEPP v2008.9, was applied to the Hermada watershed located in the Boise National Forest, in southern Idaho, USA. The results from v2008.9 and v2004.7 as well as the field observations were compared. For the period of 1995–2000, average annual precipitation for the study area was 954 mm. Simulated annual watershed discharge was negligible using WEPP v2004.7, and was 262 mm using WEPP v2008.9, agreeable with field-observed 275 mm.