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r- oo ~ N c. C. months. As a result of this depletion, many years of records indicate little or no flow entering the Virgin River Gorge during the summer months. This gorge, about 14 miles long, extends to about 4 miles above Littlefield, Arizona. The springs begin to emerge in the lower 2 miles of the gorge (see Figure 1). From this point on, flows increase to a cumulative stable inflow of about 65 ft3/s. In the summer, the springs are the major reliable source of irrigation water for the Littlefield area and downstream. Recent data indicate that the water disappearing in the influent reach is the source of the Littlefield Springs. Furthermore, this water has been analyzed using carbon-14 and tritium value methods. Tritium values have been compared with tritium values in rainfall at Las Vegas, Nevada. When adjustments are made for the rate of radioactive decay in tritium, the resulting values indicate that water entering the losing reach above the Virgin River Gorge requires a minimum travel time of 22 years before it is discharged into the Littlefield Springs. Below Littlefield, Arizona water rights totaling 65 ft3/s are held by canal companies at Hesquite, Bunkerville, and Riverside, Nevada. The major diversion takes place near Mesquite. Generally, during the summer months all flows except flash floods are diverted. Diverted water is used for irrigation during the summer months and for flushing salts from farmlands during ,the winter months. The water flowing past Riverside, Nevada which is not consumed by phreatophytes eventually reaches Lake Mead. Irrigation Diversion and Distribution Systems Eight separate irrigation diversions and distribution systems supply river water to 3,526 irrigated acres in the Virgin Valley. [2J Three systems serve the Mesquite, Bunkervi11e, and Riverside, Nevada areas. The other five of these systems are in Littlefield, Arizona area. The systems consist of lined and unlined ditches with no reservoirs for storage. 8