Road Sediment Yields from Dispersed Versus Clustered Forest Harvesting Activity: A Case Study

Road sediment yields reaching streams over a twenty year period were modeled under two scenarios for a 4900 ha forest in the foothills of the Oregon Coast Range. In the "clustered" scenario all forest harvesting activity took place in the northern half of the forest. In the "dispersed" scenario the same level of forest harvesting activity was allocated to the full forest estate. Three spatial modeling packages were used: SPECTRUM was used to schedule the harvest settings over a 150 year period, NETWORK 2000 was used to determine which roads would be used during the first 20 years of harvest and how many truck loads would be transported over them, and SEDMODL2 was used to determine the road sediment yields likely to reach a stream. Concentrating the forest harvesting activity on half of the forest estate resulted in a 36% reduction in total road sediment yields when compared with dispersed forest harvesting activity. Fewer roads would generate sediment under the "clustered" scenario but traffic intensities on these roads would be greater, partially negating the sediment yield savings.