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<br />< . <br /> <br />OOL5H <br /> <br />Task 1.140) - Consumptive Use Prototype Development <br /> <br />The growing season for crops is normally considered to extend from frost to frost. <br />For most crops, this is a reasonable way to estimate seasonal use of the Blaney- <br />Criddle, but a refinement is necessary to precisely define the growing season for <br />monthly or lO-day time steps. <br /> <br />Stage of growth is a primary variable that must be recognized since plants use more <br />water during a rapid growth phases. Variations in the growing season from year to year <br />can be expected to be larger with annual crops then with perennial crops such as alfalfa <br />or grasses. But some perennial crops have multiple halVesting times that can be <br />considered with crop coefficients. By using a lO-day time step instead of a monthly <br />time step the changes in consumptive use during periods before and after halVesting <br />can be estimated more accurately then by using a mean monthly value. <br /> <br />While it is recognized that a number of climatological factors in addition to <br />temperature (relative humidity, wind movement, sunshine hours, pan evaporation, <br />etc.) have an effect on agricultural consumptive use, a relationship can be developed to <br />use mean temperature alone to include climate variations. This is not the best method <br />for including climatic factors, but a correlation between the monthly consumptive use <br />coefficient (k) and the mean monthly temperature (t) is used in the SCS Blaney- <br />Criddle method. The shorter the time period the higher the mean air temperature tends <br />to be during peak periods. Since the consumptive use calculated by SCS Blaney- <br />Criddle is directly related to mean temperature, choosing shorter time periods will <br />result in higher consumptive use rates. Therefore using a shorter time step for <br />consumptive use estimation will increase the ability of the temperature coefficient to <br />consider temporal variations in consumptive use. <br /> <br />In order to include these variations in estimating consumptive use, the crop growth <br />stage coefficients, kt and Ie", have been introduced into the formula. <br /> <br />k = k(' kc <br /> <br />kt = Ol73t -.314, and is a climatic coefficient which is related to the mean air <br />temperature (t). <br /> <br />kt = 0173t -.314. <br /> <br />Ie" = A coefficient reflecting the growth stage of a crop. Values are obtained from <br />crop growth stage coefficient CUlVes such as those shown in figures 1 and 2. - <br />\~ <br /> <br />)C <br /> <br />2.1.4 Update Modeling Options <br /> <br />1. A preliminary design for the CU model has been developed. The CU model will <br />allow the user to calculate CU for each use category listed in the USBR "Colorado <br />River System Consumptive Uses and Losses Report". The user will be able to <br />specify the spatial area and the time period for which they want to determine the <br />water use associated with human activities. <br /> <br />2. The USBR XCONS2 model has been studied in depth. The meaning of the < y <br />different variable has been determined and the structure of the program is being <br />modified to conform with a more structure programming approach. At this time the <br />XCONS2 program is being divided into the different subroutines and these will <br />incOtporated into the overall CU model. <br /> <br />7/13/94 - Draft of Task Mernorand urn <br /> <br />5 <br /> <br />IDS Group, esu <br />