Abstract
ABSTRACT: The length and volume of granitic sediment deposits were measured annually over a 4.5‐year period below 6.6 km of forest roads constructed on headwater watersheds in the mountains of Idaho. Sediment deposits were identified by source of runoff, location of the deposit terminus, and various site factors including descriptors of hillside sediment storage capacity. Prediction equations were developed using linear regression for travel distance of sediment originating from fill slopes, rock drains, and culverts, with r2 values ranging from 0.70 for fill slopes to 0.91 for culverts. Cumulative volume of erosion and length of obstructions on the hillside were statistically significant variables in the equation for fills and rock drains; hillside gradient and runoff source area also appeared in the equation for culverts. Sensitivity analysis showed that the volume of erosion was the most sensitive variable in all cases. A dimensionless relationship relating the volume of sediment storage on slopes to sediment travel distance was also developed. This study makes it possible for land managers to assess the risk of sediment delivery to channels from alternative road designs, locations, and erosion control practices and provides a means to evaluate the cumulative effects of past road construction on sedimentation.
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