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<br />B. Project Hydrology <br /> <br />A debris flow analysis was performed by Mussetter Engineering Inc. in 1997 and is <br />appended to this report. The Mussetter study presents a I OO-year peak clearwater flow <br />for Skyrocket Creek of 540-cfs (based on COE information) and peak flow with debris of <br />1080-cfs. Total volume of debris from the I OO-year event was I~stimated at 839,500 <br />cubic feet. The Mussetter study utilized a HEC-2 model to determine depth and velocity <br />of flows at the diversion structure for 1080 cfs. V docities were estimated at 20 to 24 feet <br />per second (fps) with depth of flows estimated at 5.1 to 7.3 feet. These numbers were <br />used for the feasibility study as they have been previously accepted by the COE and are <br />acceptable to CWCB (discussions with Larry Lang). <br /> <br />The man-made diversion channel was estimated at IS-feet deep and 10-feet wide. An <br />estimate of this channel capacity is 1900-cfs using the Manning equation with channel <br />slope of 2-percent and roughness coefficient of 0.04. Actual channel capacity during a <br />debris flow may be impeded by blockage iflogs or large boulders become lodged in the <br />channel. <br /> <br />C. Field Investigations <br /> <br />On August 16, 1989 Buckhorn Geotech visited the Skyrocket Creek diversion wall with <br />staff members from City of Ouray. Buckhorn Geotech again visited the site in 1989 with <br />Larry Lang from CviCB. The conclusion of the site observations at that time was that <br />the existing diversion wall of earth, rocks, rotting timbers and broken and frayed cables <br />was in need of replacement. Photographs from these visits are attached in the appendix. <br /> <br />Topographic mapping of the diversion structure location was perfOlmed by Monadnock <br />Mineral Services in conjunction with the preliminary cost estimated for the diversion <br />structure as prepared by Ayres Associates in 1997. Resultant mapping is presented in <br />that document as appended to this study. <br /> <br />Buckhorn Geotech was asked to evaluate the rock quality and soundness for the COE in <br />2000 to verify the feasibility oftying the proposed diversion wall into surrounding rock <br />material. Field observations and tests were conducted to deternline strength parameters <br />for the formational rock at the diversion structure location. <br /> <br />D. Alternative Evaluation <br /> <br />The two primary alternatives were considered for the Skyrocket Creek drainage: <br />1. The no action alternative. <br />2. The reconstruction of the diversion wall. <br /> <br />6 <br />