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<br />the channel to determine the elevation limit of significant flood <br />evidence. <br /> <br />Sutherland Creek <br />Sutherland Creek has a drainage area of 5.37 square miles and is <br />steep in the middle part of the basin. Downstream from about 6,600 <br />feet the channel appears to have been modified because of urban <br />development and was not investigated. A small (estimated 0.4 square <br />miles) left bank tributary at an elevation of 6,380 feet is typical of <br />small drainages at this elevation. The channel is'5 feet wide and <br />flood debris is 2 feet above the streambed. The lack of vegetation in <br />the channel bottom indicates frequent flows. This suggests recent <br />flows of about 100 cubic feet per second. <br />At an elevation of 6,500 feet, Sutherland Creek has terraces and <br />gravel bars about 30 feet apart and with tops about 8 feet above the <br />channel bed. These are well vegetated with 2 inch diameter scrub oak <br />(a slow growing tree), dense brush, and near completely lichen covered <br />boulders indicating a maKimum flood. The peak discharge is estimated <br />to be about 2,400 cubic feet per second. The channel which has <br />scoured banks is about 5 feet wide and 2 feet deep, indicates a recent <br />(within the last 2 to 3 years) peak discharge of 100 cubic feet per <br />second. <br />At an elevation of 6.640 feet, just upstream from the security <br />entrance to Crystal Park Community, the channel is filled with 8 to 10 <br />feet diameter boulders in a debris-flow lobate form (although somewhat <br />washed out by subsequent water flows). The deposit is covered with <br />lichen and moss and there are many large trees growing on the deposit <br />indicating it is several hundred or more years old. A very large <br />event would have been required to transport these boulders. About 100 <br />feet upstream, the recent channel is 3 feet wide and based on lack of <br />vegetation on small in channel deposits the depth is about 2 foot. <br />Greater than this depth channel boulders are moss covered and the <br />banks are well covered with grass. Recent peak discharge (in the last <br />2 to 3 years) is about 60 cubic feet per second. On the right bank <br />there is a 10 foot by 20 foot gravel bar. The width is 30 feet and its <br />top surface is 4 feet above the streambed. There are no flood deposits <br />higher in the channel. The surface of the gravel bar has several 2 to <br />4 inch diameter spruce trees and moderate brush cover suggesting the <br />deposit is abou~ 10 to 20 years old (these probably correspond to the <br />1965 flood). The peak discharge for this maKimum flood (note that in <br />this case the maKimum flood occurred about 10 to 20 years ago) is <br />estimated to be 1,200 cubic feet per second. There are large debris <br />flow deposits from here upstream. The debris flow channel is 50 feet <br />wide and 10 feet deep. Mean velocity and peak debris-flow discharge <br />can not be estimated for a debris flow based on the available <br />information; widths and depths are provided as an indication of the <br />size of the flow. <br />EKposed slopes on the steep switchback road show very little if <br />any rill erosion. The elevation of the switchbacks vary from 6,650 to <br />6,900 feet. This would suggest that intense rainstorms are infrequent <br />at and above this elevation. <br /> <br />~ . <br />