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G:I ,1- 'i-I ly to meet the crop reqUirements. Therefore. depending on the crop it is clear that many areas of the stale re- quire additional water to meet Ihese requirements In an average year. The variation in spatial distribution of precipitation is only part of the problem. The extreme vanatlOn In precipitatIon from year 10 year and mOnlh to month forms another pattern which creates an opportunity 10 use supplemental water. For instance between 1931 and 1979 the two driest years varied from the slate's average preCIpitation by 8.26 inches short in 1934 and 8.17 Inches shon in 1936. For the same period the two wettest yeats varied by 7.60 inches over in 1951 and 6.50 inches over In 1977 (Myers, 1980). Figure 2-2 chans these annual departures In the stale for a period from 1850 to 1979 and thus is a graphic demonstra- tion of the opportunity to use and to store supplemen- tal waler in Nebraska. B. AREAS OF GROUNDWATER DECLINE Nebraska is a slate rich In both surface water and groundwater. Chapter 3 will descnbe Ihis in delail However. there are areas In the state which are ex- periencing water-level declines since predevelopment. Predevelopment water level is the approxlmale average water level that existed in a well pnor to any develop- mentlhat significantly affected water levels In Ihe VICin- ity at the well. An annual report with maps on water. level changes is prepared by the Conservation and Survey Division. Umversity of Nebraska-Lincoln and the U.S. Geological Survey (Johnson and Pederson. 1982). ThaI document shOws these declines in detail. Figure 2.3 shows Ihese declines lor 1981 at a detail which IS generalized by township. These townships are areas where the currenl demands being placed upon the groundwafer reservoir are large. Without improved management of the groundwater including severe reductions in present use and/or the Introduction ot sup- plemental water, lhese areas at some point in the luture will be unabte to support their current level at waler use. C. AREAS WITH POTENTIAL FOR IRRIGA TION DEVELOPMENT The opportunity for supplemental water development in the state (provided no constraining factors are present) is evident from an examination of the land's potential tor irrigation development. Figure 2-4 shows by township the maximum irrigation development based on land suitability. The land sUitability was de- rived from 1 :2SO,OOO-scale soil association maps which consider soil type and slopes. These maps were developed and published by the Conservation and Survey DiviSion, UniverSity of Nebraska-Uncoln and the U.S. Department of Agriculture Soil Conservation Service (Conservation and Survey DiVision, 1981). In Figure 2.4 a "well equivalent" is an Installation necessary to lrrrgate one quarter of one section (160 acres). A well equivalent IS SimIlar to the average current center. piVOt syslem as related to the area ir- rigated. It also aCknowledges technology of the center. piVot or other spnnkler systems allows for irrigation on those lands generally not adaptable to gravity syslems. The source for the well equivalent can be either groundwater or surface water. The map does not con. Sider the capabilities of the underlying groundwater reservOirs. A comparison of Figures 2.3 and 2-4 ShOws high Irrigation potential In areas of water.level decline. Figure 2.5 presents groundwater in storage in Nebraska. Comparing this map With Figure 2.4 demonstrates Ihat some areas of high potential for ir. rigalion development have very little groundwater In storage. These areas With high irrigation potential and limIted water supply are prime locations for oppor- tunities to use supplemental water supplies If they can be provIded In view of consltalnrng factors. D. AREAS WITH OPPORTUNITIES FOR SPECIFIC USES A third situation which demonstrales opportunities for use of supplemental waler is a statewide review of opportunities for specifiC uses and the areas where they occur. Six specific uses for supplemental water are con. sidered: irrigation, muniCipal, livestock and rural domestic. electric power, Industrial, and fish. wildlife and outdoor recreation. Figure 2.6 shows at a drainage. basrn level where these uses could occur. The follow- Ing discussions give some detail about the use and about locations in a basin where the use mIght occur_ 1. Irrigation Chapter 1 ollhls report and Sections A and B of this chapter have already identified Ihis use as a prime candidate for using supplemental water supply. Figures 2-3, 2-4. and 2.5 IdentIty both eXIsting and future locattons in the state for the use. Only two drainage basins. the MiSSOUtlltlbutatles and Lower Platte, have a combrnatlon of land sUitability and water.supply limita- lions that mIght not reqUIre supplemental supplies. In many olher basrns the OPPOrtUOlty for use would not be basin-wide, bUI would be restricted to areas as small as a township (36 square miles) or two. Both surface waler and groundwater could serve as the source of supplemental water for thiS use. 2. Municipal The opportunitIes for muniCipal use of supple- mental water supplies are based upon both Quantity and quality crrtena In the future, supplemental water may be needed for quality reasons at a basrn level such as In the Middle Plalte or rn commuMles 10 southeast Nebraska. Quantity problems may require additions to eXlstrng supplemental systems such as for Omaha and 2-3