Sediment production from forest roads in western Oregon

Prevention and estimation of soil erosion from forest roads requires an understanding of how road design and maintenance affect sediment production. Seventyfour plots were installed on forest roads in the Oregon Coast Range to examine the relationship between sediment production and road attributes such as distance between culverts, road slope, soil texture, and cutslope height. An additional comparison was made between road segments with cutslopes and ditches freshly cleared of vegetation and segments with established vegetation on cutslopes and in ditches. All road segments were 5 m wide and insloped with aggregate surfacing, light traffic, and no overhanging forest cover. Sediment production was correlated to the product of segment length times road slope squared. Sediment production from aggregate covered roads on a silty clay loam was about 9 times greater than that from roads constructed on a gravelly loam. Sediment production was not correlated to the cutslope height. Road segments where vegetation was cleared from the cutslope and ditch produced about 7 times as much sediment as road segments where vegetation was retained, showing the potential reduction in erosion by revegetation following construction and the potential impact of ditch cleaning during maintenance. Relationships and estimates from this study provide a basis for improved erosion estimates by commonly used empirical procedures.