SPDSS_Task93_MappingHistoricLandUse_20070109

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MEMO 93 • If there was an irrigation well (decreed or designated basin permit) in or adjacent to the parcel then the service area was not edited. This parcel will be served by groundwater only. Most of these parcels were not near an irrigation service area. • If there was a service area boundary nearby, no well nearby, and the service area could reasonably irrigate the parcel, then the service area boundary was edited to include the parcel. • If there was no service area or well nearby, then the NDVI imagery was consulted to determine if the parcel was indeed irrigated. If the NDVI imagery showed the irrigation to be questionable, the parcel was removed. In most cases these parcels were evaluated as non-irrigated. 6.2.3 Confirm Irrigated Acreage With Diversion Records Once the service areas were reviewed and all parcels were within a service area (except those parcels served by groundwater only) the acreage was summarized for the new irrigation service areas not previously mapped. This acreage was compared with reported acreage in HydroBase diversion records. Water commissioner field notes were used to supplement the 1956 parcel layer because diversion records in HydroBase were incomplete. Diversion records were compared to the mapped GIS acreage in each historic period. In many cases the exact year of each historic period was not available in the diversion records. In these cases the closest available year was used. Large proportional differences as well as overall acreage differences were evaluated when conducting the comparison. The diversions with acreage differences were revisited using NDVI imagery, orthophotos, ditches, and a DEM. In most cases the service area could be edited to more closely match the diversion records. The mapped service area was either made smaller to encompass only the immediate parcels near the diversion, or the service area was edited to more closely match an existing service area irrigated by multiple diversions. Parcels designated as irrigated parcels were reviewed once more to verify that they were irrigated. All diversion differences between records and mapped GIS acreage were resolved. 6.2.4 Assign Diversion IDs to Historic Parcels The final step was to assign the WDID from the service areas to the irrigated parcels. RTi created two models in ArcGIS model builder to intersect the service areas with the parcels and calculate the WDID into the proper attributes. The first model, shown in Appendix C.1, determined the service areas for each parcel by intersecting the centroid of each parcel with the service area polygons. Appendix C.1 shows the intersect model diagram. The second model divided the parcels into groups according to which service area each parcel is located. The results of the second model were then joined to the original parcel to calculate the correct WDID into the surface water WDID (SW WDID) attributes. Appendix C.2 shows the subset parcel model diagram. After assigning the diversion structure WDID to the parcels, the data and attributes were reviewed a final time to ensure that there were no errors. The surface water coverage (SW_COV) attributes were then populated based on the number of service areas in which the parcel was located. Attributes were reviewed for correctness. Appendix D describes the attribute review and the method for calculating the SW COV attributes. 6.3 Historic Parcel to Well Assignment 6.3.1 Assigned Wells to Parcels Based on 2001 Well Assignments Following discussion with Colorado Water Conservation Board (CWCB) and Colorado Division of Water Resources (DWR) personnel, as well as other SPDSS contractors, it was decided that the 2001 well-to- parcel assignments should be used throughout the study period. This ensures that the same land matched Page 21 of 59 ,Rrvera~Ge Feel~n81'agy, ioe.