Predicting onsite sediment yield from forest roads

Burroughs, E.R., Jr. 1990. Predicting onsite sediment yield from forest roads. Proceedings of Conference XXI, International Erosion Control Association, Erosion Control: Technology in Transition. Washington, DC, February 14-17, 1990. 223-232.

Keywords: British Columbia, sediment, impacts of roads and logging on erosion, runoff

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Abstract: A continuing Forest Service research effort to study onsite sediment yield from forest lands provides information on the relative erodibility of certain geologic parent materials and methods to reduce surface erosion. Simulated rainfall on bounded plots is the principal research tool to generate runoff and sediment yield from selected sites. This technique is also used to measure the reduction in sediment yield as a percentage of that from an unprotected site. Two types of disturbed forest sites are being studied: forest roads and timber harvest sites.

Graphs are provided to estimate the amount of erosion reduction by selected treatments on road cutslopes and fillslopes. Percentage ground cover is the principal variable to reduce surface erosion. Where data are available, graphs show estimations of the application rate necessary to provide the required amount of ground cover for a selected percentage erosion reduction. For some treatments, erosion reduction is also a function of slope gradient and silt content in the surface soil. In these cases, an erosion reduction treatment is less effective for steeper slopes and siltier soils.

The net result of controlling erosion on the various components of the forest road is not the sum, or product, of the percentage erosion reduction for each component. Research results are used to partition sediment yield from a 100-foot road section consisting of a running surface, ditch, and cutslope. This partitioning shows the expected decrease in sediment yield as each component of the road is protected, taking into account the contribution from the other components. A procedure is presented to design a rock blanket for the road ditch as a function of the expected discharge, slope, and ditch shape.

Moscow FSL publication no. 1990a