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0016'16 Operation Plan for the Proposed Long Hollow Reservoir-Preliminary Draft, March 17, 2004 6.2 Return Flows From Incremental Diversions F or Scenario 1, return flows will be 49 percent of the 2,730 AF /yr of incremental diversions or 1,338 AF/yr. On average, this equates to 1.85 cfs that will accrue to the La Plata River base flow. For Scenario 2, return flows from 1,796 AF/yr of incremental diversions will be 880 AF/yr or 1.22 cfs. Return flows from these diversions predominantly result from ditch losses, deep infiltration to the water table with subsequent hillside seepage, and accrual to the stream. Ditch water is fully applied to the field, and often in insufficient amounts. Irrigation tail water that makes its way to the stream is rare due to a short irrigation supply in the basin. Groundwater return flows accrue to the stream on a steady basis, thereby increasing base flows uniformly throughout the year. The Red Mesa Aquifer Groundwater Study (WWE, 2002) provides a basis for detennining the locations of return flows. A groundwater contour map, which was developed from water table elevation measurements in 33 wells for 17 months, was used to determine groundwater flow paths for irrigation return flows and the groundwater divide in the Red Mesa Aquifer. The groundwater divide between the La Plata River and Long Hollow is roughly coincident with Highway 140 (see Figure 7). Return flows from irrigated lands west of Highway 140 accrue to the La Plata River and lands east of Highway 140 return to Long Hollow. Return flows from the Joseph Freed, Revival, and Warren-Vosburgh ditches, which irrigate lands north of the Town of Red Mesa, accrue to the reach of the La Plata River between Cherry Creek and Long Hollow. Return flow amounts and locations from incremental diversions are shown in Table X. More to follow. 991-077.000 March 2004 Wright Water Engineers, Inc. Page 7