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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />~ <br /> <br /> <br />ROCKY MOUNTAIN ENGINEERS,INC. <br /> <br />DECEMBER 13, 1984 <br /> <br />APPENDIX 'B' <br /> <br />OURAY RANCH PROJECT <br />PHASE 2 <br /> <br />100 YEAR FLOOD STUDY <br /> <br />I. INTRODUCTION <br /> <br />A. PURPOSE AND SCOPE <br /> <br />The purpose of this study is to estimate theoret- <br />ical flood levels which may occur in the Colorado River <br />at the site of the proposed Ouray Ranch, Phase 2, de- <br />velopment. The selected recurrence interval is 100yr, <br />which conforms to various agency needs for subdivision <br />and sewerage site permit reviews. The intent of this <br />recurrence interval is to provide an estimation of flood <br />events which will only be met or exceeded once every 100 <br />yrs. The intent is not to determine the absolute maxi- <br />mum event that may occur. In this manner, design and <br />siting of improvements is done on a basis to provide <br />reasonable, substantial protection; but not absolute <br />maximum protection. <br /> <br />Projection of the 100yr event at this location goes <br />beyond the normal statistical projection of stre&m flow <br />records, since flows are directly influenced by the op- <br />eration of Granby Reservoir, 2 miles upstream. The <br />united States Bureau of ReClamation, the dam operator, <br />does not have a projection of a possible 100yr event <br />discharge. Our estimation has to be made based on storm <br />inflows, reservoir stage, spillway design, and operating <br />procedures. Granby Reservoir is designed mainly for ir- <br />rigation and recreation use; therefore the operating <br />philosophy is to fill the reservoir. But at full reser- <br />voir conditions, Granby Reservoir provides very little <br />storage capability to mitigate peak flood flows. <br /> <br />Our work therefore involves a high degree of judge- <br />ment regarding the likely combination of events which <br />may produce a 100yr flood event downstream and regarding <br />the dam operation at the time of such an occurrence. <br />The flood flows projected herein are intended to esti- <br />mate an occurrence of reasonably conservative magnitude, <br />based on reasoned judgement of the dam operation, and <br />still not be too far in excess of a normal 100yr event <br />projection. <br />Box 2, Winter Park, CO 80482 (303) 726-5166 Box 445, Kremmling, CO 80459 (303) 724-9500 <br />