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<br />• flood plains, and the large sizes in the alluvium and c.olluvium. <br />The natural stream channel, which is evident upstream of the <br />waste rock piles, has a fairly regular cross-section and the longitudi- <br />nal profile exhibits a step-pool appearance. The channel cro<_s-section <br />width is about 20 feet and bank heights are about 4 feet. The channel <br />bed, banks and the alluvial flood plain are stable, as evidenced by <br />the sediment size, lichen growth and tree sizes and appearance. The <br />channel appears stable in the sense that, although long-term changes <br />may occur, they would occur in response to high recurrence interval <br />flood or geologic events and not to the normal stream flow. A photo- <br />graph of the natural channel conditions is given in Appendix 8-3. <br />The longitudinal step-pool profile is caused by the accum- <br />mulation of large cobbles and boulders. The accumulations, as estimated <br />based upon survey information, average about 2.1 feet in heighit and 145 <br />feet in spacing. This type of profile is common to mountain streams <br />• and occurs as the stream attempts to minimize its rate of energy expen- <br />diture during high flow. The steps serve as energy dissipator•5, effec- <br />tively reducing the steep energy gradient during the high discharges <br />necessary to move the large particles and form the system. <br />Roughness coefficients or "n" values for this stream must take <br />into accnunt these bed forms as well as the sediment sizes and veg- <br />etation. Based on published "n" values for natural streams (WSP 1849), <br />as related to the photographs in Appendix 6, a "n" value for ~:he stream <br />and overbanks of 0.050 has been chosen. <br />3.5 Waste Piles <br />The two waste piles, located on both sides of Rals~:on Creek, <br />have practically an identical character. Their material is a good qual- <br />ity rockfill with sizes of fragments less than 1 foot and w~th only a <br />• <br />- 14 - <br />