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Approach and Results <br />The following individuals familiar with ground water and irrigation practices throughout the <br />SPDSS study area and other river basins in Colorado were interviewed in search of data and to <br />research opinions on deficit irrigation in the SPDSS study area: <br />• Bob Longenbaugh -Consultant Water Engineer <br />• CDM -Gordon McCurry <br />• Central Colorado Water Conservancy District -Tom Cech and Randy Ray <br />• Colorado State University -Luis Garcia <br />• DWR -Dave Nettles, Susanne Sellers, Brent Schantz, and Chris Lytle <br />• Helton &Williamsen -Jim Slattery and Tom Williamsen <br />• Leonard Rice Engineers -Jon Ford and Greg Roush <br />• Lower South Platte Water Conservancy District -Joe Frank <br />• Nation Engineering -Heath Kuntz <br />• Northern Colorado Water Conservancy District -Jon Altenhofen and Mark Crookston <br />State rules governing groundwater use and measurement requirements and historical <br />augmentation plans were reviewed. In addition, data sources found through the literature search <br />or provided by individuals interviewed were investigated. The information obtained through the <br />literature reviews and provided in the interviews is summarized in the sections below, which are <br />organized under the following categories: <br />• General Information -this section describes the factors that influence deficit irrigation <br />and opinions on whether deficit irrigation occurs and why. <br />• Power Conversion Coefficient Method -this section describes background on the power <br />conversion coefficient method and power data that maybe available through the CSU <br />archives. <br />• Historical Augmentation Plans -this section describes the method used to estimate <br />pumping under historical augmentation plans and actual pumping data that may become <br />available from augmentation plans in the future. <br />• Pumping Data Review -this section presents conclusions related to deficit irrigation <br />associated with two different datasets of pumping data. <br />General Information <br />There is consensus that deficit irrigation might occur throughout the SPDSS study area, <br />supported by observations of visible crop stress, particularly during warmer months. While <br />some of the individuals interviewed believe there is economic incentive to deficit irrigate, the <br />majority indicated that irrigators are not "intentionally" deficit irrigating. Rather, it is a result of <br />the physical system (well and pump capacity, declining aquifer levels, pivot rate, etc.) not being <br />able to meet crop demand during periods of high IWR (due to climatic conditions). For example, <br />there are times when a center pivot cannot make a full rotation prior to a portion of the irrigated <br />area becoming stressed. Deficit irrigation may also be more likely to occur on lands served by <br />ground water and/or reservoir water because pumping and reservoir releases can be scheduled as <br />opposed to direct flow surface water supplies. <br />Task 77.doc 2 of 8 <br />