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<br />C) <br />C) <br />~ <br />~'~t <br />'-,:1 <br />~ <br /> <br />171 <br /> <br />5.5.1.2 Municipal and Industrial Depletions <br /> <br />Base-line values for annual municipal and industrial depletions <br /> <br />are obtained from the Comprehensive Framework Study (l971; Table 2, <br /> <br />page 24) and from the USBR (1971b). <br /> <br />Annual values are distributed uniformly over the months of <br /> <br />the year. <br /> <br />5.5.1.3 Irri~ation Consumptive Use <br /> <br />Depletions for irrigated agriculture are modeled in terms of <br /> <br />the volume consumed through crop evapotranspiration. In practice, an <br /> <br />amount of water is diverted to the area being irrigated and the portion <br /> <br />of the water not consumed either enters the ground water system by <br /> <br />deep percolation or returns to the stream as surface or subsurface <br /> <br />flow (Hyatt et a1., 1970; Ch. IV). Eventually all of the water not <br /> <br />consumed returns to river channel to become either surface or sub- <br /> <br />surface streamflow. Lag-times for return flows may be on the order <br /> <br />of hours for surface return flows or years for ground water flows, and <br /> <br />depend upon the distance of the irrigated lands fro~ the river channel. <br /> <br /> <br />By modeling only irrigation depletions, an assumption is <br /> <br />made that return flows occur within the basic time period of one month. <br /> <br />Since most of the irrigated acreage in the Upper Colorado Basin is <br /> <br />adjacent to the stream channel from which depe1tions are made this <br /> <br />assumption is justified, at least to first order. <br /> <br />For all levels of depletion,annua1 agricultural consumption is <br /> <br />distributed over the months of the growing season, April through July, <br /> <br />in the percentages specified in Table 2.1 (see Chapter 2). <br />