America's Northern Plains
An Overview and Assessment of Natural Resources
Water Supply
Rainfall and snowmelt are the primary water sources in the mountains of the western Northern Plains region. Spring and early summer rains, local alluvial aquifers, and large regional aquifers, such as the High Plains or Ogallala and Big Sioux, are major water sources for the region's central and eastern plains (USGS, 1986).
However, the High Plains aquifer has been mined significantly, and recharge rates are not keeping pace with agricultural withdrawals. Areas of declining water levels coincide with areas of most rapid irrigation expansion (Figures 7 and 8).
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Figure 7. Water level changes in the High Plains Aquifer, pre-development to 1980 (Weeks and Gutentag, 1981). |
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Figure 8. Water level changes in the High Plains Aquifer, 1980-1990 (after Dugan and Schild, 1992). |
Surface waters, including the Missouri, Platte, Arkansas, and their tributaries, plus the High Plains Aquifer, are the major water sources for the west central, central, and eastern parts of the region. As one moves eastward, precipitation increases during the growing season, supplying most crop needs for most years in MLRAs 102A, 102B, 106, and 107. Surface waters and aquifers provide water for domestic needs.
Water supply issues will become increasingly important across the region as urban centers grow and as agricultural water uses, including irrigation, expand. Urban demands rose with an expanding population, and irrigation increased 2.7% (400,000 acres) from 1982 to 1992.
Roughly 18 million acres of cropland in the region are irrigated. Nebraska showed the largest gain (8.4%) in irrigation from 1982 to 1992, accounting for 41% of the irrigated cropland in the entire region. Colorado experienced the largest decrease (3.8%) among the seven states.
Currently, three-quarters of irrigated cropland is under cultivation. Most of the rest supports hay production. Agricultural uses of surface and groundwater account for 86% of total water withdrawals among the Northern Plains states.
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