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<br />u01075 <br /> <br />Operation Plan for the Proposed Long Hollow Reservoir-Preliminary Draft, March 17, 2004 <br /> <br />four ditches. Therefore, on average, most ditches only divert water during the nmoff period from <br />mid-April to mid-June. No new lands will be irrigated in Colorado as a result ofLHR. <br /> <br />6.0 INCREMENTAL DIVERSIONS <br /> <br />Incremental diversions for the 14-year period were allocated to 18 Colorado ditches. Average <br />incremental diversions for each ditch are shown in Table 4. These incremental diversions will <br /> <br />supplement the existing (and short) supply for each of these ditches as a direct result of LHR <br />storage. Incremental diversions typically will occur during the runoff period from mid-April to <br />mid-June, although incremental diversions occur as late as August during some years such as <br /> <br />1996 (see Figure 9). <br /> <br />6.1 Depletions from Incremental Diversions <br /> <br />Incremental ditch diversions average 2,730 AF/yr for Scenario 1 and 1,796 AF/yr for Scenario 2 <br />during the study period (see Table 4). A basin-wide irrigation efficiency of 51 percent was used <br />for these diversions, i.e., depletions of 51 percent and return flows of 49 percent. This irrigation <br />efficiency assumes that: <br /> <br />1. Each AF of incremental water is diverted twice within Colorado. <br /> <br />2. 30 percent depletion for each AF diverted. <br /> <br />Mathematically, depletions = (1.0 AF x 30% depletion) + (0.7 AF x 30% depletion) = 0.51 AF or <br />51 percent. A 51 percent irrigation efficiency is conservative because: <br /> <br />. The vast majority of Colorado ditches use flood irrigation, which has low efficiency, and <br />ditch losses are significant due to soil conditions and ditch length. <br /> <br />. Most L percent) of the incremental return flows accrue to the La Plata River below the <br />Cherry Creek confluence, and there are only three Colorado ditches that can divert these <br />return flows so two diversions for each incremental AF of water is not likely. <br /> <br />991-077.000 <br />March 2004 <br /> <br />Wright Water Engineers, Inc. <br /> <br />Page 6 <br />