| OCR Text |
Show ROADS General Discussion " Forest roads have a significant impact on the hydrologic functioning of the watershed. Increased runoff resulting from construction of miles of Forest roads and the associated erosion, can and does seriously damage the watershed. Roads have been a major contributor to the increase in sedimentation resulting from on- the- ground development and use. In some areas, as much as 90 percent of the increased sediment production caused by use of the National Forest has been attributed directly or indirectly to construction and use of roads. " In the life of a road, there are three critical periods. First is the construction stage during which soil is being manipulated. Second is the curing stage which lasts from completion of construction to approximately 3 years while soil is extremely erodible. Third is the long- term life of the road during which natural climatic factors act on a somewhat more stable road prism. All three periods of road life are important although rates of erosion are highest during construction and curing periods and diminish thereafter ( assuming new activity is not initiated). Several factors including wind, precipitation, frost; and drying affect erosion. For example, raindrop impact is as important in displacing material as overland flow on steep slopes; frost lifts particles and then upon melting allows them to roll under force of gravity to lower elevations; wetting or drying soil causes the disintegration of some soil and rock aggregates through changes in pore pressure and moisture tension within the soil mass; wind moves soil particles if the soils and cover conditions are right. Wind erosion has been observed as a major problem on fill slopes in Idaho. Although all the physical properties of the soil, geology, and climate affect the rates and magnitudes of sediment produced from a road prism, slope steepness and slope length interacting with storm characteristics seem to be the most important. " Sediment yields from areas undergoing intensive development are often 500 to 100 cimes greater than 279 |
