Recent findings related to measuring and modeling forest road erosion
Elliot, W.E.; Foltz, R.B.; Robichaud, P.R. 2009.
Recent findings related to measuring and modeling forest road erosion.
In Anderssen, R.S.; Braddock, R.D.; Newham, L.T.H., eds.
Proceedings of the
18th World IMACS / MODSIM Congress, Cairns, Australia, 13-17 July 2009.
International Congress on Modelling and Simulation.
Interfacing Modelling and Simulation with Mathematical and Computational Sciences.
Keywords: WEPP:Road, ditch, road surface, inslope, outslope, FS WEPP, road
PDF (300 KB)
Sediment is the greatest pollutant of forest streams. In the absence of wildfire, forest road
networks are usually the main source of sediment in forest watersheds. An understanding of forest road
erosion processes is important to aid in predicting sediment delivery from roads to streams. The flowpath
followed by runoff is the key to understanding road erosion processes. On rutted roads, the flowpath
follows ruts until a cross drain structure or change of grade is encountered, leading to considerable
sediment delivery. Insloping roads to bare ditches can lead to ditch erosion, but if the ditch is graveled or
vegetated, erosion is generally minimal. Outsloping a road minimizes the flow path length on the road,
minimizing surface erosion, and runoff is dispersed along the hillside, minimizing delivery. If roads have
low or no traffic, the road surface may become armored, reducing erosion rates by 70 to 80 percent. If there
is no traffic, and a road becomes covered in vegetation, erosion may drop 99 percent, but the hydraulic
conductivity of the road surface is only minimally affected. In many cases, forest buffers absorb road
runoff, minimizing the delivery of road sediment to streams. Buffers are less effective in wetter climates in
absorbing runoff and reducing sediment delivery. Cutslopes can erode, making sediment readily available
to be transported from roads. Graveling reduces the likelihood of rut formation, generally leading to a
significant decline in road erosion. Traffic, however, can reduce the effectiveness of gravel by pressing it
into the subgrade, or breaking it down. Paving a road will reduce road surface erosion, but may increase
erosion in road ditches and on the hillsides or channels in a buffer area. If water is delivered from road
cross drains to a channel, the chances of delivering sediment increases, as does the chance of entraining
additional sediment through channel erosion. Empirical (USLE and SEDMODL) and process-based
(KINEROS and WEPP) models have been applied to road erosion. SEDMODL and WEPP have been
specifically adopted to model road erosion, and to account for the important detachment and delivery
processes. A version of WEPP is available online that is receiving widespread use in the USA and
throughout the world. This tool can either analyze single segments of road between cross drains, or can
analyze up to 200 segments in a single run. Areas needing to be improved in road erosion are modeling the
armoring process within a storm, developing the probabilistic capabilities of WEPP for road applications,
adding mass wasting to the WEPP technology and expanding the WEPP road soil database.
Moscow FSL publication no. 2009n