PROJ00387 - Laserfiche WebLink

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. CONCLUSIONS AND RECOMMENDATIONS 1. Rio Grande Dam was found to be a high hazard structure. Dam failure would cause extensive property damage and would poten- tially cause loss of life. 2. The existing Rio Grande'Dam would be overtopped by the one-half probable maximum flood if the reservoir were full prior to the flood. Dam failure would probably occur. The dam presently has sufficient surcharge and spillway capacity so that the 500 year rainflood can be passed without the dam being overtopped. Over- topping would not occur even if the 500 year rainflood occurs during the snowmelt runoff season. 3. The probable maximum flood can be passed by the existing facili- ties without overtopping the dam only if the reservoir is empty prior to the flood. The one-half probable maximum flood can be passed if the reservoir storage content is limited to 40,000 acre-feet. . 4. The one-half probable maximum flood can be passed by the exist- ing spillway without overtopping if the dam crest is raised six feet to elevation 9469, even if the reservoir is full prior to the storm. Approximately 26,000 cubic yards of material would be required for the dam enlargement. 5. The probable maximum flood can be passed if the spillway is enlarged and if the dam crest is raised ten feet to elevation 9473. Spillway enlargement would include excavation of about 55,000 cubic yards of material and placement of about 4,800 cubic yards of structural concrete. The spillway would be widened to about 120 feet at the maximum section. The present width is 32 feet. Material excavated for the spillway enlargement would be placed on the downstream face of the dam. . -7-