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MEMO -TASK 91 <br />Analyze <br />opography for Land Above and <br />Diversions and Ditches <br />^ Diversions <br />^ DEM <br />^ Ditches <br />^ Hydrography <br />Digitize <br />Service Area <br />Boundaries Using ArcMap <br />QAQC <br />Service Area Boundaries for <br />Consistency and Positional <br />Accuracy <br />Attribute Service Area <br />With Diversion ID and Ditch <br />Name <br />^ Preliminary <br />Irrigated Parcels <br />^ Orthophotos <br />^ 1:24,000 DRG <br />Figure 2. Steps In Mapping Preliminary Irrigation Service Area Boundaries <br />The topography was analyzed using several different data: preliminary irrigated parcel boundaries, USGS <br />digital raster graphics (DRG) at 1:24,000 scale, hydrography data (including ditches and canals), <br />diversion structures, and a digital elevation model (DEM). The hydrography data was obtained from the <br />Colorado Division of Wildlife (CDOW). CDOW digitized streams, ditches, and canals from 1:24,000 <br />DRG maps for intended input to the USGS National Hydrography Dataset (NHD) in the 1990's. This <br />dataset was used to identify and map ditches. <br />The first step was to identify diversion structures and analyze the topography above and below each <br />diversion and ditch. Appendix A lists the 154 key diversion structures that were obtained from the <br />SPDSS Consumptive Use Contractor. Key diversions were extracted from HydroBase, identified, <br />mapped, and matched to a ditch. Diversion structures were matched to a ditch spatially, by matching <br />names, and by matching water source. The land that potentially could be irrigated by each diversion <br />structure was identified by highlighting the land above and below that diversion structure and ditch. A <br />Digital Elevation Model (DEM) was used to analyze the topography. <br />The second step required digitizing the irrigation service area boundaries by starting at the diversion <br />structure and following the ditch out to its end. The lower end of each service area was bounded by a <br />drainage, river, or by another major ditch. Figure 3 shows diversion structures and ditches with elevation <br />data identifying land above and below the ditch. The yellow boundaries are the digitized irrigation <br />service areas. The preliminary irrigated parcel data was used to highlight areas of irrigation within a ditch <br />service area. Service areas were only digitized around potentially irrigated parcels. The service area <br />boundaries were digitized at a scale between 1:2,000 to 1:8,000 depending on the complexity of the <br />service area. <br />After the service area boundaries were digitized, a check for accuracy and consistency was conducted. <br />The initial check was based on the DEM, digital raster graphics (DRG), and preliminary irrigated parcels. <br />The DEM was used again to ensure that the land within a service area boundary could be irrigated by a <br />gravity system. The DRGs were used to identify any cultural features or obstacles that might block the <br />delivery of irrigation water. One exception was made in evaluating the irrigation service areas. `Islands' <br />of high elevation land within a service area were not excluded; however, it was understood that it may not <br />be possible to irrigate these areas from the ditch. The final check on the data was for correct topology. <br />Page 3 of 55 ~R~versfde FecAno[o`(!~Y fnc. <br />4'JaYer Resources Errgi~ecr:np an~i L~ar+suFlrnd <br />