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. . delineating irrigation ditches in irrigation practice (i.e. ditch. within fields unless there was a significant difference irrigated versus non-irrigated) on either side of a a Final irrigated acreages and the consumptive use calculated for those acreages were compared to traditionally derived values. Appendix A shows the irrigated acreages and consumptive use for each hydrologic unit by county. Irrigated acreages calculated in this project were 9% less and consumptive use was 6.7% less than figures derived by traditional methods. Appendix A also discusses the methods used by the Salt Lake City regional office to calculate consumptive use. t- :> <:r.l "'-l DISCUSSION The irrigated-lands database created for the Upper Gunnison basin was designed to take advantage of the best features of three types of image data sources: orthophoto quadrangles, CIR,aerial photography, and multispectral satellite imagery. Orthophotos offer high sp.tial resolution and planimetric accuracy that meets national map-accuracy standards but have only limited spectral information. The spectral characteristics of CIR aerial photography are ideal for mapping irrigated lands, but they are sUbject to tilt and relief displacement in their geometry. Neither the orthophotos or the CIR photography are ordinarily available for the times in the growing season of interest. Satellite imagery, such as SPOT or Landsat TM (thematic mapper) and MSS,: offers the spectral characteristics and timeliness to establish irrigation statu$ information at the time and place for which it is required. Through appropriate use of techniques of image processing and GIS, the best characteristics of all three inform~tion sources have been brought together in a single data base. The nature of the da~abase is such that it can be easily updated in future years by acquiring and processing new satellite imagery to create new irrigation status and intensity attributes for each field. If any new fields are brought under irrigation, they can be easi~y added to the database without having to redigitize any of the existing data. Because the database is digital and geographically referenced, it will also be easy to add other data layers that may be deemed important in future years. The Upper Gunnison basin database was created on a system capable of exporting files in U.S. G.ological Survey DLG (Digital Line Graph) tape format, which will facilitate sharing the database with other organizations. Many Colorado River basin states have remote sensing and GIS capabilities similar to those of Bureau of Reclamation and U.S. Geological Survey and USGS. Mapping irrigated lands in the Upper Gunnison basin as described here may point the way to a standardized approach for compiling irrfgated acreages throughout the Colorado River System. LITERATURE CITED ESL, INC., 1987a., Instruction Manual ESL-IM237, Ver. 4.2. Sunnyvale, California, 350 pp. ESL, INC., 1987b, GES (Geographic Entry System) Manual, TM1739, Ver. 8.74. Sunnyvale, California, 275 pp. Kauth, R., P. Lambeck, W. Richardson, G. Thomas, 1979. Feature Extraction Applied to Agricultural Crops as Seen by Landsat. In: Proceedings of the LACIE Symposium, NASA LBJ Space Center, Houston, Texas, pp. 705-721. Verdin, J., 1985.' Inventoryof Irrigated Lands and Reservoir Surface Areas in the Upper Green River Basin. Technical Memorandum 85-4-8. Bureau of Reclamation, Applied ScienCes Branch, Denver, Colorado, 22 pp. Verdin, J., C. Hay, and M. O'Grady, 1985. A Sampling Approach to Irrigated Acreage Determination in the Green River Basin of Wyoming. Proceedings of the 1985