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<br />" <br /> <br />North Fork Gunnison <br />1/18/2006 <br />Page 2 <br /> <br />. <br /> <br />Division of Water Resources. These estimated existing consumptive water uses do not <br />include irrigation rights, only springs and ponds used for domestic, stock and evaporation <br />uses. <br /> <br />GIS Analysis methodology <br />The eastern portion of Water District 40 was divided into 17 subbasins as shown in Figure 1 - <br />at the end of this document. The subbasins were further subdivided by county. The <br />Crawford subbasin, for example, spans all three counties and was subdivided into Crawford <br />Delta, Crawford Gunnison, and Crawford Montrose. Only 7 of the subbasins, however, are <br />potentially impacted by the proposed in stream flow filings and the results summarized in <br />this memorandum are for those 7 subbasins. <br /> <br />Future water use was estimated for each subbasin using landuse breakdowns, irrigated acres, <br />and population estimates derived from the GIS coverages. Land uses for the entire study <br />area are shown in Figure 2 - at the end of this document. For each subbasin, landuse acreage, <br />irrigated acres for each landuse type, parcel breakdowns, and population estimates, were <br />calculated using ArcGIS 9.1, and are shown in Appendix A. The following discussion <br />describes the methodology and assumptions used to obtain the desired quantities. <br /> <br />Landuse analysis <br />The land use parcel coverages were intersected with the subbasin coverage, resulting in <br />land use parcels with the subbasin attributes and matching subbasin boundaries. The <br />intersect tool in ArcGIS splits a feature (in this case a land use parcel polygon) with another <br />specified feature (subbasins), where they overlap; therefore, if a landuse parcel polygon <br />overlaps two subbasins, the parcel will be split into two polygons when the intersect tool is <br />used. If a landuse parcel polygon extends beyond the subbasin boundary, the intersect tool <br />will only retain the portion of the landuse parcel polygon within the subbasin boundary. <br />After intersecting the coverages, the area of each landuse parcel was recalculated, and the <br />attribute tables were exported to Excel. <br /> <br />. <br /> <br />Irrigated acres for various land use classifications were determined by intersecting the <br />irrigated acre coverage with the subbasin coverage, resulting in a new irrigated acres <br />coverage with the attributes of the subbasin coverage, and matching boundaries. This <br />intersected irrigated acre coverage was then unioned with the land use coverage to obtain <br />irrigated acres for each subbasin with various landuse classifications, and matching land use <br />boundaries. The union tool, like the intersect tool, will split features at overlapping <br />boundaries and add the attributes of each coverage, however, the union tool will retain all <br />portions of the two polygons, not just the overlapping portions. This tool is helpful when <br />features outside the extent of the "clipped" feature must be retained. The irrigated acre area <br />was recalculated after the union, and the attribute table was exported to Excel. <br /> <br />. <br /> <br />S:\SWSI 2\North]0I1<\finaLmemoldeliverable011606\CWCB N FOI1< 1-17 -OO,dOC <br /> <br />