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1.0 EXECUTIVE SUMMARY <br />The purpose of the irrigated lands assessment was to determine the extent (i.e. ditch service area <br />boundary and irrigated parcel boundary), and character (i.e. crop type) of irrigated lands in the Rio <br />Grande Basin. The character (i.e. land cover class) ofnon-irrigated lands within the ground water <br />model area was also determined. Four GIS products were developed as part of the RGDSS irrigated <br />lands assessment: <br />1) a ditch service area theme was produced to delineate the service area boundaries of the <br />surface water structures in the basin, <br />2) a composite false color satellite image was developed to serve as a raster backdrop to other <br />GIS themes, <br />3) an irrigated parcel theme was developed to delineate the boundary and important attributes <br />of the irrigated parcels within the basin, <br />4) a land cover classification theme (delineating irrigated and non-irrigated land types) was <br />developed to assist in determining the consumptive use of the non-irrigated portions of the <br />basin. <br />Ditch Service Area Theme. The ditch service area theme was developed to show the service area <br />boundaries for surface water ditch systems. Existing maps were digitized. Thirty-five interviews <br />with water users were held to delineate ditch system service boundaries. An additional thirty-nine <br />interviews and two public meetings were held to verify and refine the ditch service area boundaries. <br />The service area for 633 structures within the basin was mapped encompassing an area of 965,765 <br />acres. Effort was concentrated on delineating the ditch service area for ditches within the ground <br />water model area. However, ditches within the mountain areas with easily assessable information <br />regarding service area were also mapped. Service area boundaries represent the area of land that the <br />ditch has the physical ability or legal right to irrigate. The entire service area of each ditch system <br />may not be indicative of the amount of lands that were irrigated during the 1998 season because <br />service areas typically include fallow fields, farm houses, non irrigated corners, roads, lands served <br />by more than one ditch, etc. The Ditch Service Area Theme is displayed in Figure 3 of this report. <br />Composite False Color Theme. A composite false color infrared satellite image of the entire basin <br />was developed to serve as a raster backdrop for other GIS themes. This composite image was <br />developed from two August 1998 Landsat Thematic Mapper (TM) images. The Landsat satellite <br />imagery was also used to create a land cover classification providing an indication of the crop type <br />grown on the irrigated lands and the land cover class associated with non-irrigated lands. Indian <br />Remote Satellite (IRS-1C) satellite imagery was used to delineate irrigated parcel boundaries that <br />were hand-digitized. The False Color Infrared Image of the Entire Basin is shown in Figure 8 of this <br />report. <br />Irrigated Acreage Parcel Theme. The irrigated parcel theme was developed for the valley floor in <br />1998 using Landsat andIRS-1C satellite imagery in conjunction with other available data to create a <br />vector-based geographic data set of irrigated lands A total of 612,739 acres was classified as <br />irrigated in 1998. This estimate of total irrigated acreage for maj or harvestable crops agreed within <br />