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<br />V. Description of Data and Software: South Platte Consumptive Use Model (SPCU) <br /> <br /> <br />A typical way to allocate water supply to meet <br />demand in excess of precipitation is to assign the <br />surface supplies first with the remaining demand <br />being met by wells. Another option is available <br />that applies the demand to both sources evenly, <br />each supplying half of the demand not met by <br />precipitation. <br /> <br />2..i..Q Evapotran~piration Estimation CET) <br />Methods <br /> <br />The SPCU Model allows users to select <br />methods for estimating ET and to produce <br />output that shows comparisons for the estimates <br />calculated using different methods. <br /> <br />· Blaney-Criddle - This is a monthly method <br />that was developed initially by the Natural <br />Resources Conservation Service (formerly <br />the Soil Conservation Service) and uses <br />temperature, precipitation, and crop data. <br />This method can be used with calibration <br />factors (i.e. monthly multipliers) and a <br />sprinkler spray loss can also be entered for <br />sprinkler irrigation systems. <br /> <br />Figure 7: SPCU Model Well Information Window <br /> <br />· Kimberly-Penman - This method calculates <br />ET based on monthly values from reference <br />crop ET from NCWCD weather stations. A <br />sprinkler spray loss factor can also be used <br />with the Kimberly-Penman method. <br /> <br />· Penman-Monteith - This method operates <br />on a daily time step and requires detailed <br />climate data for determining the reference <br />crdp ET. The Penman-Monteith method only <br />computes crop ET and can not be used in the <br />farm soil water balances with surface and <br />groundwater supplies. <br /> <br />2.5.7 Monthlv Precioitation Methods <br /> <br />Two precipitation methods can be used for <br />effective rainfall. An option exists which can <br />affect the soil moisture budget when rainfall is in <br />excess of consumptive use for crops in a given <br />month by allowing excess effective rainfall to be <br />stored in the soil. <br /> <br />l.SCS (Soil Conservation Service) - <br />Precipitation method, based on the SCS <br />methodology, in which effective rainfall is <br />dependent on the net depth of application <br />and the average monthly consumptive use. <br /> <br />20 <br /> <br />Completion Report: South Platte Mapping and Analysis Program <br />