Road surface erosion models

NCASI is distributing Technical Bulletin No. 988, Comparison of Road Surface Erosion Models with Measured Road Erosion Rates. The authors are Kathy Dubé (Watershed GeoDynamics), Tom Black and Charlie Luce (US Forest Service Rocky Mountain Research Station) and Mark Riedel (W.F. Baird and Associates, Ltd.). Cooperating organizations included Temple-Inland Corporation, Plum Creek Timber Company, Stephen F. Austin State University, Colorado State University, Oregon State University, and Oklahoma State University.

This report summarizes measurements of road erosion and runoff from nine sites across the United States and uses them to test the performance of three popular road erosion models (WEPP, GRAIP, and SEDMODL2). Without local calibration, none of the models predicted absolute values of annual erosion well at all of the sites. Two performed better at between-road segment comparisons, but there were still unexplained differences between observed and predicted sediment losses from the road datasets tested. This comparison of model performance with measured road erosion highlights the need for additional research and the limitations of model-only assessments of forest road impacts.

The easiest model to use is the Internet-based WEPP:Road interface developed by the US Forest Service. This interface has limited choices for road conditions, but it is convenient for modeling a few segments or testing the model’s sensitivity to different input values. The PC-based WEPP, GRAIP, and SEDMODL2 require installation on a PC. The PC interface of WEPP provides the user with the ability to vary a large number of input variables, but most users do not have the detailed soil and management data needed to select appropriate values for many of the variables. GRAIP uses site-specific road condition data as well as a local estimate of surface erosion rates. SEDMODL2 uses GIS data, and can be run with generalized or site-specific road conditions.

The road surface erosion models tested in this study are appropriate for the relative comparison of erosion between segments and between management conditions. If accuracy and precision are needed for a particular application, measurement of surface erosion to provide calibration data at a particular site is an appropriate solution.

Member company employees, as well as government and academic personnel, may request a printed complimentary copy of this report by sending an email to publications@ncasi.org or by calling (919) 941-6400.

The report is also available for download by NCASI members at www.ncasi.org. Members needing a password should contact Pam Bruns (pbruns@ncasi.org).