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A. <br /> <br />r- -I <br />604 <br />The snowpack on the mine area generally starts accumulating during November <br />and remains on the ground until late April or May of the following year. <br />Measurements of snow depth indicate the snow water content generally <br />increases with time. A discussion of precipitation is presented in Sec. 2.1.2. <br />2.7.6.2 Evapotranspiration <br />Evapotranspiration occurs as the result of evaporation from soil and <br />transpiration by the vegetative cover. The amount of available soil water <br />lost to the atmosphere from a given area depends on the type of soil and <br />vegetation cover. It is also closely related to climatic factors, prin- <br />cipally precipitation, temperature, wind velocity, radiation intensity and <br />relative humidity. <br />The evapotranspiration values used in this study were calculated using <br />the Blaney-Criddle (1962) method as modified by Dorenbos and Pruit (1975). <br />This approach allows correction of potential evapotranspiration for vari- <br />ations in local conditions with respect to relative humidity, intensity <br />of radiation and wind velocity. A method of Thornthwaite (1957) for <br />accounting for the effect of soil moisture on evapotranspiration rates <br />was also used. This was done by application of Thornthwaite's moisture <br />retention table. These calculations indicate the monthly evapotrans- <br />piration varies between 0 and 12 cm (see Table 2.7-23). <br />2.7.6.3 Surface Runoff <br />Due to the anticipated steep topography of the reclaimed area, some fraction <br />of the incident precipitation will run off. It will be lost to overland <br />2-527