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• 3.4 Channel Characteristics The channel characteristics of bed slope, width and depth in Ralston Creek are controlled both by the canyon bedrock into which the stream is incised and the alluvial and colluvial sediments of the canyon floor. The bedrock appears to serve both as a grade control and as a restraint to lateral migration in various reaches. The sediment materials are hard and angular to subangular in shape and range from several feet in diameter to gravel and finer sizes. The canyon is narrow and constricted in the areas upstream and downstream of the mine facility and waste pile site. Slopes are very steep and the bedrock canyon wall and outcroppings control t;he stream boundaries. Locally, streambed slopes are over 4 % in these areas. There are numerous areas of colluvium, debris flows and talus slopes in addition to pockets of alluvial materials in the streambed. • The mine and waste pile site is located in a flatter and wider alluvial valley. Slopes are as low as 1.6 % in parts of this reach. The alluvial materials are widely varied; sizes range from approximately 16 inches to sands and gravels. There are very few fines with only about 10 % of the material less than the No. 20 (1 mm) sieve size. Appendix A, Plate A-9, shows a gradation curve for the alluvial material. The material ranges from subangular to angular in shape, indicating that streambed movement has not played a dominant role in its transport. Occasional larger size angular rocks are found in the alluvium. It is apparent that the larger materials are derived from rockfalls, debris flows and colluvium and are not mobilized by stream flows. Their eventual disintegration to particle sizes which may be transported by the stream is a result of weathering near their source (Leopold, Wolman and Miller, 1964). There appears to be an ample supply of sediment availab]e; the small sizes in the alluvial pockets and the • - 13 -