Navajo Lake and Cedar City water supply

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C14 CONTRIBUTIONS TO STREAM-BASIN HYDROLOGY Spring and 60 percent to Duck Creek Spring, as shown in the test of August 2-7 when all the sinks were covered by water and also in the hydrograph for both years 1954 and 1955 (fig. 12). When increased flow to the sink area is of short duration, such as July 15-17 and 24-27,1955 (fig. 12B), the difference in time of travel from the sink area to the respective springs and the nor­mal recession curves must be considered when evaluating the amount of increased flow for each spring. When these adjustments are made, the apportionment of increase is consistent with that shown for longer periods of time. The discharge of both Cascade Spring and Duck Creek Spring increased considerably more than the release to the sink area for the periods August 11-20 and 24-30, 1955. This increased flow was caused by precipitation in the basin and shows that both springs receive water from other sources than Navajo Sinks. This subject is discussed further under the heading, "Other sources of water in major springs." Precipitation at Cedar Breaks during August 9-18 was 3.07 inches and August 22-25, 2.61 inches. During high-water years when there were several months of continuous flow into the Navajo Sinks and when there was little or no contribution directly from rainfall or snowmelt, the proportional discharge of Cascade Spring was as follows: July-September 1957, 43 percent; June-September 1958, 40 percent. 6. Regulation of outflow from Navajo Lake by exist­ing structures, which provide for release of con­trolled storage water to the sink area during the irrigation season, does not materially change the proportions of water going to Cascade and Duck Creek Springs; however, the seasonal distribu­tion can be changed by the amount of controlled storage water (1,378 acre-ft) between the spill­way crest and the outlet pipe. If the dike is raised in the future to a higher elevation to pro­vide additional controlled storage, the seasonal distribution could be changed materially. OTHER SOURCES OF WATER IN MAJOR SPRINGS 7. Cascade Spring receives water other than that flow­ing to it from the Navajo Sinks. After cessation of flow from the lake into the sinks, Cascade Spring has continued to flow for periods of 95-125 days at a rate of less than 3 cfs in the first month and less than 1 cfs in subsequent months-a small increment that is probably derived by seepage from the lake and from the ridge that intervenes between lake and spring. Cascade Spring was dry for periods of 50-160 days in each of the win­ters of 1955-57. Cascade Spring also receives water directly from snowmelt and from rain upon the ridge separating it from Navajo Lake. The peak discharge in both 1957 and 1958 occurred 15-30 days before Navajo Lake reached its maxi­mum stage but at the time of maximum melting of snow. At other times also the spring discharge has increased during periods of snowmelt or rain­storms, and the contemporaneous rise in lake level was insufficient to account for the discharge as originating from the sinks alone. 8. Duck Creek Spring, likewise, receives water from other sources than Navajo Sinks. This is shown when the sinks receive no water for extended periods, yet the spring discharge does not decline below about 0.5 cfs. Records also show that in each year the maximum monthly discharge of Duck Creek Spring has exceeded the total amount of water entering the Navajo Sinks during that month. The surface drainage area above Duck Creek Spring is six times as large as that tribu­tary to the Navajo Sinks. 9. The water issuing from Duck Creek Spring flows eastward about 2% miles and then enters the Duck Creek Sinks, which have adequate intake capacity for the greatest flow (226 cfs) ever measured in Duck Creek. Since 1954 the dis­charge of Asay Creek below Lower Asay Spring has ranged from 13 cfs, when the entire flow was from Upper and Lower Asay Springs, to 419 cfs, which included overland runoff from melting, snow. Although the water entering the Duck Creek Sinks contributes to the water of Lower Asay Spring, it is not the only water discharged by that spring. Upper Asay Spring is about 2,000 feet up­stream from and 25 feet higher than Lower Asay Spring. Its flow is less than one-fourth (18 per­cent during the fall of 1953) of the flow of Lower Asay Spring and was not seen to be affected by the artificial release of water or of fluorescein into the Duck Creek Sinks. 10. Mammoth Spring is 10 miles northeast of Navajo Lake and separated therefrom by a major topo­graphic divide; its orifice is about 900 feet lower than the Navajo Sinks. The artificial release of water and of dye into the Navajo Sinks and Duck Creek Sinks had no observed effect upon the water discharged at Mammoth Spring. The discharge of Mammoth Spring is ordinarily more than