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i 3 <br />~ the soil surface fr+cm raindrop detachment, a very effective sediment oorttrol <br />system is developed. <br />Methods which rely primarily on settling of sediment (e.g. diversions, <br />detention stivcturesj will be most effective on larger ~~~*+* sizes <br />(specifically fine through coarse sand). Usually adequate detention times can <br />not be developed behird structures of this type to reduce the amount of finer <br />~__~^* particles. <br />Any effective sec~„+pnt carittol system for a small (or large) area will <br />rwr~,;rc+ a stable ocrlveyance system. A concentrated flow of water can cause <br />significant damage if it is not confined to a stable corrmeyance ~han.,Pi. <br />Otx~e the erosion control groups are selected, the designer must then select <br />the most appropriate and cost effective individual design type within each group. <br />Many erosion control types can be eliminated simply on the basis of (I) <br />availability of material or equipment, (2) specific climate conditions or (3) <br />nature of the mining operation. his type of review and selection of structures <br />or measures should reduce the number of alternatives to a reasonable number. <br />A physical process appxoadi to sediment control will quickly identify which <br />structures or measures will be most effective. Trial and error selection of <br />erosion catttrol q~~ can be eliminated by utilizing the concepts of this <br />approach. <br />'IY1e formation of soil is a very slow geologic process, as is the erosion of <br />soil by wind arxi water. In mast ,~;~,*~ areas the rate of soil formation <br />exceeds the rate of natural soil erosion. Where man's activities d;~t„rt, the <br />soil surface and remove the protective vegetative Dover, the erosion process is <br />often accelerated. When the rate of accelerated erosion exceeds the rate of soil <br />formation, lard degradation wi11 occur. If accelerated erosion is allowed to <br />~~ <br />W <br /> <br />