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These sources were not complete enough to be analyzed. Specifically, both sources are limited <br />by not having associated PCCs and the first source is limited because it only provides annual <br />totals. <br />Historical Augmentation Plans <br />Prior to the early 2000's, there were no decreed augmentation plans or approved substitute water <br />supply plans within the SPDSS study area that were based on pumping records. The standard <br />practice was to base augmentation requirements on pumping demand predicted using an IWR <br />method, typically modified Blaney-Griddle. As discussed in the Task 58 Review Previous <br />Estimates of1'otential CUmemorandum, the Colorado Revised Statues direct applicants to use <br />the modified Blaney-Griddle method to calculate depletions associated with wells for diversions <br />that are not actually measured. Some irrigators did maintain pumping recorded by flow meters <br />or estimated pumping using power records and PCCs. Within the SPDSS study area, irrigators <br />were not required to certify flow meters and PCCs, which are both very sensitive and without <br />proper calibration, can result in records that are not representative of actual pumping. <br />Several recently decreed lower South Platte augmentation plans have augmentation requirements <br />based on actual pumping records multiplied by an application efficiency (generally 80% for <br />sprinklers, 60% for flood). Under some of the larger augmentation plans, users will maintain <br />both flow meter readings and power data that can be used with a certified PCC to estimate <br />pumping. Meters are in the process of being installed and certified. In the coming years, records <br />associated with these new decrees will be valuable for investigating deficit irrigation. <br />Pumping Data Review <br />The GASP (Groundwater Appropriators of the South Platte) database was developed primarily <br />from user-supplied information. Most of the information in this database was derived from <br />power records that were not certified and included estimated pumping and application <br />efficiencies. Based on discussions with individuals who have reviewed and worked with this <br />database, while it may have been sufficient for other uses, its error range is too large to estimate <br />deficit irrigation. <br />Central Colorado Water Conservancy District and other districts are in the process of installing <br />(and certifying) flow meters on individual wells. While Central has some metered flow records <br />available from the past several years, a quota has been applied during this period. The quota <br />limits pumping to a percentage of the estimated demand. With restricted pumping, the records <br />may not be representative of the entire SPDSS study period and therefore were not considered <br />appropriate for characterizing deficit irrigation. <br />Pumping records were requested from several other ditch companies and water districts. The <br />majority of the contacts indicated that pumping records were not available or that they could not <br />obtain the individual users' permission to release the data. Two potential data sets were <br />provided: (1) monthly pumping records associated with several wells located on the eastern <br />plains of the South Platte River Basin, and (2) annual pumping estimates associated with the <br />Northern High Plains area. <br />Task 77.doc 5 of 8 <br />