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6.0 Comments and Concerns <br />The historic crop consumptive use estimates are based on measured and recorded data; <br />information from other studies; information provided by local water commissioners and <br />users; and engineering judgement. The results developed for this project are considered <br />appropriate to use for the RGDSS planning and administration efforts. Areas of potential <br />improvement or concern include: <br />Historic Acreage. The 1998 irrigated acreage, which serves as the basis for estimating <br />historic acreage, is considered very accurate. Acreage estimated based on aerial <br />photography or satellite imagery for years prior to 1998 could provide a better <br />estimate of historic acreage than the use of County Agricultural Statistics. <br />Conveyance Efficiencies. As discussed in Appendix B, conveyance efficiency <br />studies have been prepared for several of the larger ditch systems in the basin, but <br />little information exists for the other large ditch systems or the smaller systems. <br />Future canal loss studies could improve the estimate of conveyance efficiencies used <br />in the historic consumptive use estimate. Conveyance efficiency estimates used in <br />the analysis are based on soil type and ditch length, determined by the GIS canal <br />coverage. The canal coverage was digitized from previous mapping, and does not <br />include all ditches or the entire length of some ditch systems. More detailed mapping <br />of ditch systems in the Rio Grande could improve the estimate of conveyance <br />efficiencies. <br />Application Efficiencies. The results presented herein include readily available data <br />and engineering estimates for maximum flood irrigation and maximum sprinkler <br />irrigation efficiencies. However, the results are sensitive to those efficiency <br />estimates. For example an increase in the sprinkler irrigation efficiency could result <br />in a corresponding decrease in ground water pumping. Similarly, an increase in <br />maximum flood efficiency could result in an increase in consumptive use from <br />surface water, a decrease in pumping and a decrease in consumption by ground water. <br />Additional refinement could occur if additional data were developed to refine these <br />estimates on a ditch by ditch basis. <br />Well Data. As noted in Appendix A, the well to irrigated acreage association task <br />highlighted missing information in the State's well permit database. Information was <br />missing for wells assigned to approximately 25,000 acres out of over 326,000 acres <br />assigned to wells (less than 7 percent of total ground water acreage). Updates or <br />improvements made to the database should be incorporated into future estimates of <br />historic consumptive use. <br />Natural Sub-Irrigation. The consumption of ground water by irrigated lands through <br />natural subirrigation has not been included in the historic consumptive use analysis. <br />Therefore it is possible that this analysis has over-estimated the amount of man <br />controlled consumptive use. For example, if sub-irrigated lands are supplied by <br />surface water only, too much of the diversion could be considered consumptive and <br />attributed to a man induced activity. Similarly, if sub-irrigated lands have a ground <br />water supply, pumping estimates may be overestimated and man controlled <br />agricultural consumptive use maybe overestimated. Future enhancements to the <br />cureport_6-2004.doc 47 of 48 June, 2004 <br />