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<br />o <br />C") <br />N <br />~ <br />00 <br />N <br /> <br />The above complexities required the use of water supply spread <br />sheets for each ASA. The water supply summaries both for the SRF <br />and MCC comparisons in Figure 4 are based on the following equations: <br /> <br />(l) Depletions <br />Exports. <br /> <br />Consumptive Use + Evaporation - Imports + <br /> <br />(2) Natural Modified Flow = Present Modified Flow + Depletions <br />- ,Groundwater Withdrawals. <br /> <br />(3) Future Modified Flow = Natural Modified Flow - Depletions <br />+ Groundwater Withdrawals. <br /> <br />Pledse note that in most of the estimates shown in Figure 2 and <br />3 for groundwater withdrawals and consumptive use it has been assumed <br />that irrigation on the high plains would consume all of the water <br />withdrawn for that purpose. In some situations this is a vaild as- <br />su~ption. However, in other situations the consumptive use on the <br />High Plains may be less than withdrawals by 10 percent, more or less, <br />depending on the texture of the soils and the amount of water pumped <br />and for other reasons. Groundwater irrigation accounts for most of <br />the groundwater withdrawals in ASA's 1103, 1105, and 1106. <br /> <br />Comparisons of State/Regional Futures (SRF) with Modified Central <br />Case (MCC) data as shown in the following figures have been made for <br />base year 1975. Such comparisons illustrate that some significant <br />differences occur largely because the sources of data as well as some <br />of the assumptions and criteria used in compiling the data are <br />different. In some cases the trends or magnitudes of the data still <br />reveal that potential problems relating to growth, recession, or <br />magnitude of water requirements exist even though there are differences <br />in the basic estimates from the two ,sources. <br /> <br />There are many differences exceeding ten percent in the SRF data <br />as compared to the MCC data for 1975 based on data shown in Figures 1 <br />through 4 for the seven ASA's and Region. Rough statistical summaries <br />have been made in three ranges: <br /> <br />First, where differences are within 10 percent, <br /> <br />Second, where differences range from 10 to 50 percent, and <br /> <br />. <br /> <br />Third, where differences exceed 50 percent. <br /> <br />24 <br />