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<br />O,l) 1 j 6 9 <br />Task 1.14(b) - Consumptive Use Prototype Development <br /> <br />The methodology for including winter precipitation into the Enhanced USBR BC and <br />the PM Reference crop methods will consider the contributions of winter precipitation to <br />the overall soil moisture budget. This method will allow the user to enter Management <br />Allowed Depletion (MAD) values for each month of a growing season and for each crop <br />type over the time period being considered. This value could become very low at the end <br />of the growing season before harvesting to model the farmer cutting the irrigation water <br />in anticipation of harvesting the crop. The precipitation through the winter will be added <br />into the soil moisture budget based on soil melt efficiency, but no more than field <br />capacity. The precipitation efficiency is a percentage value that can be entered by the <br />user for each month. The precipitation efficiency will be multiplied by the total <br />precipitation and will result in an amount of effective precipitation that will be added to <br />the soil moisture budget. <br /> <br />3.2 Agricultural Consumptive Use <br /> <br />Although there are many categories for consumptive use, agricultural consumptive use <br />is probably the most important, since 64 to 69 percent of consumptive use on upper basin <br />tributaries of the Colorade river is agricultural (U.S. Bureau of Reclamation <br />Consumptive Uses and Losses Report for 1981-1985). Agricultural consumptive use is <br />composed of the irrigated acreage, livestock, and stock pond categories. <br /> <br />A main computational program for consumptive use was developed in FORI'RAN that <br />incozporates the subroutines for calculating CU for irrigated crops and other categories. <br />The other categories include stock-ponds, livestock, reservoir, municipal, industrial and <br />export, there are self-contained modules within the main program. <br /> <br />3.2.1 Evapotranspiration Calculation Methods <br /> <br />Agricultural consumptive use is primarily water use by crop evapotranspiration (ET). <br />ET is the amount of water used by vegetation growth and evaporation from adjacent soil <br />or plant foliage. <br /> <br />For the CROSS CU model, a review of literature has been done as part of Phase I to <br />evaluate ET equations, methods and models that could be adopted for estimating total <br />agricultural consumptive use. ET estimation equations, methods and models differ in <br />meteorological data requirements, applicability, and accuracy. <br /> <br />There will be four methodologies (original USBR BC, Enhanced USBR BC, PM <br />reference crop method for alfalfa, and the PM reference crop method for grass) which <br />will be used to calculate the ET for the CROSS CU model. The methodologies have been <br />developed as component programs written in FORTRAN, the origin of the <br />methodologies are: <br /> <br />Oril!inal USBR BC <br /> <br />. Obtained from the XCONS2 FORTRAN program and developed by the USBR. <br />This program has been documented and modified to make it more structured. <br />XCONS2 uses the Blaney-Criddle (BC) method with modifications adopted by the <br />Soil Conservation Service (SCS). This method is commonly referred to as SCS <br />Modified Blaney-Criddle (SCS-BC). This method has been used by the USBR to <br />prepare the "Colorado River System Consumptive Uses and Losses Report," and <br />therefore is an excellent way to build on work done in the past. The CROSS model <br /> <br />9/30/94 . September Update (1.14-9) <br /> <br />4 <br /> <br />IDS Group, CSU <br />