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Historic irrigation data were collected from a variety of sources.
Maps were obtained from the Nebraska Department of Natural Resources
(NDNR) and the Natural Resources Conservation Service (NRCS).
The NDNR maps contain a detailed 1980 irrigation inventory for
South Central Nebraska. These maps identify irrigated fields for
the following counties: Dawson, Gosper, Phelps, Furnas, Harlan,
Buffalo, Franklin, and Webster. Irrigated areas for other counties
was determined using data provided by the NRCS. NRCS land cover
maps were developed for 27 counties within the COHYST study area.
The source dates for these land cover maps range from 1977-1981
and the maps identify irrigated and non-irrigated cropland. Counties
included are: Adams, Box Butte, Buffalo, Butler, Chase, Clay,
Custer, Dawson, Franklin, Frontier, Furnas, Gosper, Hall, Hamilton,
Harlan, Hayes, Hitchcock, Howard, Kearney, Nance, Nuckolls, Phelps,
Platte, Polk, Red Willow, Webster, and York. For these counties
it will be assumed that areas irrigated between 1977-1981 were
also irrigated in 1982. In some areas the 1997 irrigation layer
previously developed by CALMIT was edited using the above mentioned
historical sources and including the Pathfinder Irrigation District
and other irrigation maps obtained from the Nebraska Department
of Natural Resources. These paper maps identifying surface water
irrigation rights were digitized using ArcInfo. The canal project
maps include; Castle Rock, Steamboat, Chimney Rock, Empire, Midland-Overland,
Graf Canal, Keith-Lincoln, North Platte Canal (Platte Valley I.D.),
Paxton-Hershey, Birdwood, Suburban, Cody-Dillon, Western Canal,
Thirty Mile Canal, Six Mile Canal, Cozad Canal, and Orchard-Alfalfa
Canal. Maps were individually digitized and then merged into one
map. Irrigation data was also obtained from the Central Nebraska
Public Power and Irrigation District. This layer was checked for
accuracy using 1982 NRCS field data and registered irrigation
well data current to 1982. Multi-date Landsat 3 satellite imagery
were also used to help identify field boundaries.