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000486 , / NAVAJO RESERVOIR AND NEW MEXICO WATER RIGHT OPERATIONS Navajo Reservoir was constructed by the USSR in the late 1950's as a principal storage component of the Colorado River Storage Project (CRSP). The reservoir is operated to store surplus water available during the spring runoff months in the San Juan, Piedra, Navajo and Pine (Los Pinos) rivers in southwestern Colorado and northwestern New Mexico. The stored water is subsequently released during the mid to late summer months to provide supplemental and full service irrigation water supplies and supplemental municipal and industrial uses on the lower reaches of the San Juan River in New Mexico. Navajo Reservoir is a rolled earthfill embankment constructed across the main stem of the San Juan River about 34 miles east of Farmington, New Mexico. The reservoir has a total capacity of 1,708,600 acre-feet of which the active capacity is about 1,036,100 acre-feet. the remainder of the storage consists of 659,900 acre,feet of inactive capacity and a dead storage pool of 12,600 acre-feet. At its normal high water line, the surface area of the reservoir is about 15,610 acres. The reservoir holds a junior New Mexico storage permit with a 1955 priority. This represents a junior water right relative to the major existing irrigation and industrial water rights on the San Juan River in New Mexico and the reservoir is also junior to most of the major water rights decreed for diversion from the San Juan, Navajo, Piedra and Pine rivers in Colorado. For purposes of the CROSS, the reservoir should be assigned an arbitrary priority that is junior to all existing water rights in Colorado (i.e. a 1995 water right) since the reservoir cannot call out upstream junior water rights. Flood control, recreation and fishery flows are secondary operating purposes for Navajo Reservoir that are accomplished by using monthly water supply forecasts provided by the National Weather Service. Under normal conditions, the reservoir is operated in an attempt to fill by the end of the snowmelt season. Using the monthly forecasts, a release schedule is developed which will fill the reservoir, meet downstream demands and reserve the flood surcharge pool above the spillway crest for accommodation of summer rain floods. The forecasts are updated monthly (or more frequently as necessary) and the release schedule is modified accordingly. Normal releases are made through the outlet works although at critical high flows, releases can also be made through the auxiliary outlet works and the headworks of the NIIP diversion in an effort to fill the reservoir without encroaching significantly into the flood surcharge pool during the snowmelt season. The forecasted inflow is adjusted for known upstream depletions, in particular the transbasin exports by the San Juan,Chama Project and filling operations of Vallecito Reservoir. The USSR has developed a flood control/drawdown diagram to regulate the releases. Fundamental to this tool are the following assumptions: (1) The surcharge pool above elevation 6,085 (total reservoir capacity '" 1,708.600 acre-feet) is reserved exclusively for rain floods; (2) During critical high runoff flows, releases can be made through the outlet works, the auxiliary outlet and the headworks for the NIIP diversion; and (3) The reservoir will not be drawn down below elevation 5,990 feet (capacity '" 659,900 acre-feet). Use of this flood control/drawdown diagram results in downstream releases well below the existing capacity of the downstream channel. 21