. Effect of logging roads on sediment production rates in the Idaho Batholith. Sediment production during the first time period after construction was extremely high on Watersheds 1 and 2 but decreased rapidly in subsequent periods. However, this didn't occur on Watershed 3. A survey of sediment flow was conducted May 8, 1962, to examine this anomalous behavior on Watershed 3. The downslope movement of sediment on each watershed was mapped from its source to its downslope terminus. This is easily done because of the light color, the coarse texture, and the uniform gradation of the eroded mater
. Effect of logging roads on sediment production rates in the Idaho Batholith. Sediment production during the first time period after construction was extremely high on Watersheds 1 and 2 but decreased rapidly in subsequent periods. However, this didn't occur on Watershed 3. A survey of sediment flow was conducted May 8, 1962, to examine this anomalous behavior on Watershed 3. The downslope movement of sediment on each watershed was mapped from its source to its downslope terminus. This is easily done because of the light color, the coarse texture, and the uniform gradation of the eroded material in this area (fig. 3). The cause of the limited sediment production on Watershed 3 was readily apparent; a barrier of logs and debris in the drainage bottom was catching the material en route (fig. 2). Sediment flow phenomena have been noted elsewhere and research has shown that natural and/or artificial barriers delay and reduce coarse sediment movement downslope (Trimble and Sartz 1957; Haupt 1959; Packer and Christensen 1964). Additional erratic behavior was noted on Watershed 3. A natural landslide scarp existed on this watershed prior to road construction. This type of slide, classified as a debris avalanche (National Research Council, Highway Research Board 1958), is characterized by rapid downslope movement of soil and rock material having varying Figure 4.—View of the lower jammer road in Watershed 33 where the debris avalanche originated because of a road fill 6. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Megahan, Walter F. cn; Kidd, Walter J. Ogden, Utah : Intermountain Forest & Range Experiment Station, Forest Service, U. S. Dept. of Agriculture
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