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gaps between GIS coverage years at the ditch-specific level of resolution as desired under <br />Task 71. <br />Relative priority of irrigation water rights were also reviewed to determined if they could <br />be used to help predict crop type or acres of irrigated land at the ditch or well level. The <br />analysis indicated that total acres of irrigated land remained relatively constant over time <br />for acreage irrigated with surface water only or irrigated with surface water and <br />supplemented with ground water, regardless of the irrigation right priority, unless rights <br />were transferred to municipalities. In contrast, irrigated acreage increased over time for <br />lands served only by ground water. The analysis also indicated that changes in crop type <br />could not be determined by the priority of an irrigation right. <br />Hydrologic conditions during the four GIS coverage years were evaluated and it was <br />determined that they could not be used to predict changes in crop type or irrigated acres. <br />Based on the evaluation, we recommend the following procedure for filling crop type <br />data at the ditch or well level: <br />Lands Irrigated with Surface Water Only or Supplemented with Ground Water <br />1. Fill Crop Type for 1956 Coverage: Use 1976 GIS coverage to fill crop type for <br />1956 coverage. In instances where parcels from the 1976 GIS coverage are <br />spatially identical or overlap parcels in the 1956 coverage, use the 1976 crop type <br />to fill the 1956 parcel. Parcels that existed in 1956 but do not overlap with <br />parcels in 1976 should be filled with the crop type of the 1976 parcel that is <br />located nearest to the 1956 parcel. <br />2. Back Fill Acreage and Crop Type from 1955 to 1950: Use acreage and crop types <br />from the completed 1956 GIS coverage to back fill to 1950. <br />3. Linear Interpolate Acreage and Crop Types from 1957 to 1975: Use acreage and <br />crop types from the completed 1956 and 1975 GIS coverages. Use astraight-line <br />interpolation between individual crop acreage, add individual crop acreage to get <br />total. <br />4. Linear Interpolate Acreage and Crop Types from 1977 to 1986: Use astraight-line <br />interpolation between individual crop acreage, add individual crop acreage to get <br />total. <br />5. Linear Interpolate Acreage and Crop Types from 1988 to 2000: Use astraight-line <br />interpolation between individual crop acreage, add individual crop acreage to get <br />total. <br />6. Forward Fill Acreage and Crop Types from 2002 to 2005: Use acreage and crop <br />types from 2001 GIS coverage to forward fill to 2005. <br />Lands Irrigated with Ground Water Only <br />1. Fill Crop Type for 1956 Coverage: Use 1976 GIS coverage to fill crop type for <br />1956 coverage. In instances where parcels from the 1976 GIS coverage are <br />spatially identical or overlap parcels in the 1956 coverage, use the 1976 crop type <br />to fill the 1956 parcel. Parcels that existed in 1956 but do not overlap with <br />Page 10 of 11 <br />