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,j t~ \-7:':,J' ~' ~..., f,!>~. :' j 'li't~.,. :1 (2) Operational! Pumping from the Durango Pumping Plant to Ridges Basin Reservoir could occur throughout the year, but most of the water would be pumped during the annual spring runoff when flows in the Animas River were highest. Pumping would be regulated to allow 125 cfs in the winter and 225 cfs in the Summer or natural flow, whichever was less, to bypaas the plant, to help preserve the river's ecosystem and appearance, The amount of bypass would be determined by the downstream nonproject demands with prior water rights and the demand for project municipal and indus- trial water in New Mexico. Because of the pumping pattern, Ridges Basin Reservoir would generally be at its maximum level during May and reach its maximum capacity in 19 of the 49 years studied. Because of the demand pattern, annual reservoir drawdown would generally be at its maximum during July and August, averaging about 22 feet annually, or less than 8 percent of the maximum water depth as measured at the dam, This drawdown usually would OCcur entirely within the recreation season of April through September, decreasing the average surfsce area from 2,160 to 1,950 acres. In poor water years or periods of extended drought, the drawdown would be greater. During the 49-year study period, drawdown would have exceeded 22 feet in 26 years. Additional information on reservoir drawdown is presented in Table A-4, and the reservoir's end-of-month content for typical wet, normal, and dry years is presented in Attachment 1. Table A-4 Ridges Basin Reservoir Drawdown Drawdown Feet Acre-feet Minimum annual 3.4 7,000 Average annuall/ 22 47,000 Maximum annual- 40 84,000 Maximum monthly 17 35,000 1/ Occurs entirely during the recrea- tion season, April through September. -~ ~.. ">' ",~ ~.:--; ,,~ Although the project would allow for the delivery of 8,200 acre-feet of municipal and industrial water on an average annual basis for the Durango area, about 90 percent of the supply, as shown in . Figure A-5, would be turned out from the inlet conduit before reaching the reservoir, treated, and delivered through the Durango Municipal and Industrial Pipeline. The remaining supply actually stored in the reser- voir would be released by gravity back to the inlet conduit whenever water was not being pumped to the reservoir, usually in late summer. J; \.: ,," ~ " ~ '::;- 1/ Operations of project features were studied using a computer simulation based on hydrologic data for the 49-year period from 1929 through 1977 (Bureau of Reclamation, 1979), A-IS