Sediment production from granitic cutslopes on forest roads in Idaho, USA

A series of 75 non-bordered plots was used to measure surface erosion on gr anitic road cuts on forest roads in the mountains of Idaho. Erosion data we re collected for four years following road construction. Erosion rates for the first winter period after construction averaged about five times greate r than the average of erosion rates for subsequent seasons. Both mass and s urface erosion processes were observed on road cuts with mass erosion parti cularly important during the first season after construction. Regression an alysis showed slope gradient, slope aspect, ground cover density and snow-f ree period rainfall erosivity had statistically significant effects on eros ion. Slope gradient was by far the most influential site factor affecting e rosion but slope length had no affect. Three erosion control treatments - d ry seeding, hydroseeding plus mulch, and terracing with hydroseeding plus m ulch - were evaluated. Two treatments - dry seeding and hydroseeding plus m ulch - caused statistically significant reductions in erosion. Dry seeding was the most cost-effective treatment on sites with deep alluvial soil. Els ewhere, hydromulching was the most cost-effective treatment. Further testin g is needed to evaluate the effectiveness of erosion control treatments dur ing the first period after construction. We were unable to discriminate bet ween erosion rates on the moderately to highly weathered granitic rock incl uded in this study. A discussion of the application of the study results is presented. Copyright (C) 2001 John Wiley & Sons, Ltd.