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<br />o <br />-.J <br />~ <br />CO <br /> <br />18 <br /> <br />exports. The surface outflows are usually read in as data since the <br /> <br />outflow point of a hydrologic area is usually selected <;It a stream gaging <br /> <br />station, while the ground water outflows on a large area such as the <br /> <br />Grand Valley are usually estimates. Evapotranspiration losses are <br /> <br />handled in subroutines PCUS and ACUS. <br /> <br />Subroutine PCUS <br /> <br />The potential consunlptive use is the quantity of water than can <br /> <br />be evaporated and transpired i~ sufficinet wate:r of acceptable quality <br /> <br />is available. Two methods were used to compute consunlptive use, <br /> <br />Blaney-Criddle and Jensen-Haise, but only the Blaney-Criddle method <br /> <br />was programmed. The purpose of having two functions is to provide <br /> <br />a comparison between computations of evapotranspiration which is <br /> <br />important when considering the large magnitude of such depletions. <br /> <br />Usually, the evapotranspiration is expressed in inches, but in order <br /> <br />to make these figures compatible with other budget items, they have <br /> <br />been converted to acre-feet. The land use classification system <br /> <br />employed in this model is listed in Table 3. <br /> <br />Blaney-Criddle method <br /> <br />The Blaney-Criddle method of computing evapotranspiration <br /> <br />involves the determination of consumptive use as a function of temper- <br /> <br />ature and percent daylight hours. The general equation is expressed <br /> <br />as, <br /> <br />> <br /><i <br />