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MOISTURE MOVEMENT <br />The quanY.ity of water which enters a watershed as precipitation <br />equals the amount of water which leaves from the watershed by <br />runoff, Evaporation, transpiration and deep percolation, plus <br />that whi<:h is stored in the soil or other reservoirs. The evapo- <br />transpirational (evaporation from vegetative and soil surfaces <br />plus water loss resulting from plant transpiration) losses which <br />occur during dry periods must be replaced by rainfall or snowmelt <br />during wept seasons before water moves into groundwater aquifers <br />where it may ultimately contribute to the base flow of regional <br />streams (Wymore 1973). As elevation increases, evapotranspira- <br />tion decreases. For example, the evapotranspiration of spring <br />seeded western range grasses has been measured at 26.8 inches <br />at 5,000 feet elevation, 19.6 inches at 6,000 feet, 12.7 inches <br />at 7,000 feet and 9.3 inches at 8,000 feet (Berg et al. 1973). <br />• A study by Wymore (1973) developed an estimate of the water <br />balance on the processed shale disposal area (Davis Gulch). <br />This study used the Jensen-Haise method of estimating evapotran- <br />spiration which is based on the assumption that evapotranspiration <br />is not limited by precipitation. This method involves an evaluation <br />of the ratio of evapotranspiration to solar radiation as a function <br />of air temperature. The Jensen-Haise method was developed from <br />measurements of crops grown under given conditions of solar radiation <br />and air temperature. An example is well-watered alfalfa with 12 <br />to 18 inches of top growth providing 100 percent ground cover. <br />The Jensen-Raise method was developed for mean air temperatures <br />of 40° to 90°F and provides an estimate of zero evapotranspiration <br />at a mean daily temperature of about 26°F. This method was modified <br />somewhat to meet the particular climatic conditions of the Piceance <br />Basin. The modification involved a regression analysis of pan <br />evaporation divided by solar radiation versus air temperature, and <br />. was based on pan evaporation and temperature data from Montrose, <br />E-24 <br />