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An investigation was made to determine areas of Infiltration and areas and amounts of recharge to the Navajo Sandstone in the lower Dirty Devil River basin In south-central Utah. Techniques used in the Investigation are described. Information gathered using neutron emitting and receiving equipment indicated that small quantities of water infiltrate sloping surfaces of the sandstone outcrop. Larger quantities Infiltrate where the Navajo Sandstone underlies areas of ponding and alluvium-covered channels. Moisture-retention curves were developed for cores obtained at outcrops of the Navajo Sandstone. The hydraulic conductivity of the rock was determined using data from these curves In empirical equations. Recharge values were computed for two areas using hydraulic conducitivIty and in-situ rock-suction measurements. No recharge occurred on the sloping surface of the Navajo on Waterpocket Fold during the summer thunderstorm season of 1977. During the same period, 0.32 Inch or 14 percent of the precipitation recharged the Navajo on Thousand Lake Mountain. Deuterium and oxygen-18 concentrations in water samples of precipitation, streamflow, spring flow, and ground water indicate that the source of recharge to the Navajo is pr i mar i ly preci pi tat ion that occurred I n the f a I I, w inter, and early spring. Ratios of carbon-14 and carbon-12 isotopes in samples of ground water indicate an unadjusted age of between 7,000 and 33,000 years. The "younger" water samples collected at the Waterpocket Fold indicate a recharge area nearby. Statistical analyses of nine sets of discharge measurements on the Fremont River as it crosses the Navajo Sandstone outcrop at Waterpocket Fold show the I oss or gai n to be no greater than about 2 to 3 percent of the total flow. Total recharge to the Navajo Sandstone outcrop in the study area Is estimated to be about 4,000 acre-feet per year from preci p itati on and 2.000 acre-feet per year from streams. INTRODUCTION During 1975-77, the US. Geological Survey. In cooperation with the Utah Department of Natural Resources, Division of Water Rights, made a study of bedrock aquifers in the lower Dirty Devil River basin area, Utah (Hood and Daniel son, 1979). One objective of that study was to determine the areas and amounts of recharge to the Navajo Sandstone of TrlassicC?) and Jurassic age. a major aqui f er in the study area. The purpose of th i s report is to describe the techniques used to accomplish that objective and to present the findings.

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Seven reservoirs in central Colorado, operated by the Denver Board of Water Commissioners, were studied to determine evaporation losses. These reservoirs, Elevenmile Canyon, Oil Ion, Gross, Antero, Cheesman, Williams Fork, and Ralston, are located on both sides of the Continental Divide. The period of study was 19&7-73. Evaporation was computed by the energy-budget and masstransfer methods, and from evaporation-pan relationships. For three reservoirs, Elevenmile Canyon, Oil Ion, and Gross, mass-transfer coefficients were calibrated by energy-budget studies. At the remaining reservoirs, an empirical technique was used to estimate the mass-transfer coefficient. The energybudget-calibrated methods give the most accurate evaporation values; the empirical coefficients give only a best estimate of evaporation. The pan method of computing evaporation is the least reliable method because of problems of advected energy through the sides of the pan, representative pan exposure, and the variability of ratios of reservoir to pan evaporation. Total evaporation for the seasons is not known because instrumentation rafts were not operated during the entire open-water season. Calculation of evaporation (sublimation) amounts from the ice cover was not attempted, but the amounts are believed to be small. Amounts of evaporation during the longest single period of record at each of the three reservoirs for which energy budgets were determined are: