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The Integrated Decision Support (IDS) Group at Colorado State University is studying how <br />satellite imagery can be used to investigate crop consumptive use, crop stress, and effects of <br />salinity. This research is mainly focused on studies in the Arkansas River Basin. Based on a <br />review of information developed for a limited area and time period of the lower South Platte <br />River basin, this type of research may be useful in the future for investigating deficit irrigation <br />through identifying crop stress. The IDS Group has identified crop stress under parcels using <br />sole source wells as the supply, particularly for lands on the south side of the South Platte River <br />in areas with sandy soils. <br />Information from studies in the Arkansas and Republican River Basins regarding irrigation <br />pumping versus consumptive use studies indicates that the level of deficit irrigation is not <br />consistent. For example, in the Arkansas, it is not unusual to pump more than would be <br />predicted by the consumptive use methods because of water quality issues. In the Republican, <br />where greater aquifer depths drive pumping costs up, pumping is consistently less than estimated <br />by the consumptive use methods. The South Platte does not have the same water quality issues <br />as the Arkansas so "over" pumping is not expected to the extent found in the Arkansas. Nor <br />does the South Platte have the aquifer depths of the Republican River Basin, so the economic <br />incentive to deficit irrigate is not expected to be as strong. To characterize deficit irrigation over <br />an expansive area, a representative sample of wells need to be investigated. For example, soil <br />properties vary greatly throughout the South Platte River basin. Several people interviewed <br />indicated they would expect deficit irrigation to occur more in areas with sandy soils because the <br />soils cannot retain moisture as effectively. <br />In summary, the primary factors identified by individuals interviewed that influence deficit <br />irrigation include: <br />• Soil type <br />• Climatic conditions <br />• Time of growing season <br />• Crop type <br />• Whether the well serves as a sole source or supplemental supply <br />• Irrigation system capacity (well, pump, sprinkler) <br />• Aquifer level <br />Power Conversion Coefficient Method <br />The most direct way to investigate the extent of deficit irrigation occurring throughout the <br />SPDSS study area is to compare monthly pumping records to IWR estimates divided by an <br />application efficiency. For this comparison, the acreage and crop type associated with the <br />pumping records are needed to calculate the IWR. In the absence of flow meter records, electric <br />power records could be used with power conversion coefficients (PCCs) to estimate pumping. <br />The development of PCCs requires several parameters to be estimated including depth to ground <br />water, pumping capacity, and pump efficiency. These parameters are site specific and can <br />change over time. <br />In the mid 1990's DWR adopted Rules Governing the Measurement of Tributary Ground Water <br />Diversions Located in the Arkansas River Basin. Under these rules, the PCC approach can be <br />Task 77.doc 3 of 8 <br />