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I'Ll 1.1 Chapter 3 Supplemental Water Supply The three baSIC components that may comprise a supplemental water,supply development are discuss- ed in this chapter. The first sectIon identifies sources of surlace water and groundwater supplies in Nebraska. The second section outlines methods for transfer 01 supplemental water, Finally, the Ihlrd sec, lion discusses the potentials lor surface-water and underground-water storage in the state. This study does not identify specIfic supplemental water prOjects by location of source, storage or use. However. a wide range of sites is presented in the third section which have been studied for surface water storage, A. SOURCES OF SUPPLY 1. SURFACE WATER Surface water can be used in a variety of supple- mental water projects. The water can be impounded at its source or in the area of Its use or both. II can be diverted into variOus transler systems. Surface water can be used to recharge groundwater reservoirs which are connected and adjacent to II. These uses can be met by both flowing and standing surface water. In Nebraska the surface water which is available for supplemental supply is found in the state's hundreds of miles 01 flowing streams. including the Missouri River, . '<.~ ,..:1 ....~ #:,:. ~tl.~~" ~ ~ C!~-- ,-1~ ~ -r !io -_ ~. ol::....~~... .- - .-;. ...... "-"'. .'... '."",~, J ... Figure 3-1 shows by line width the discharge of Nebraska's principal rivers in water year 1975. In thaI year Nebraska received a tinle less waler by inflow and precipitation than usual. The supply received was not as well distributed as in some years. Total outflow amounted to 6.7 million acre-feel. In Figure 3-1 abrupt decreases in line width indicate points of major diver- sions (D), and abrupt increases in line width indicate points of major returns (A) or tributary inflows. Com- plete breaks in fines represent onstream reservoirs. By far the greatesl part of streamflow leaving Nebraska is discharged directly into the Missouri Aiver, which defines Ihe state's east boundary. The remainder of the outllow is to South Dakota, Colorado, and Kansas. Despite the intensive use of water in the Plalte Aiver drainage basin, Ihe Platte Aiver's annual discharge to the Missouri during the decade preceding water year 1975 ranged from about 47 percent to 62 percent and averaged about 55 percent of the total outflow from the slate. The Niobrara River, which also discharges into the Missouri, produced from 8 to 19 per- cent and averaged about 14 percent of the total outflow during the same decade. In water year 1975, the con- tributions of these two rivers to the flow of the Missouri were about 51 and 14 percent, respectively. of the total outflow from Nebraska. The Republican, Little Blue, Big Blue, and Big Nemaha rivers together produced about 20 percent of the state's outflow in the same year, The greatest potential for supplemental supply may be the Missouri Arver which annually discharges at Sioux City, Iowa. over 25 million acre-feel. four limes the state's outflow (Bentall and ShaHer, 1979). Figure 3-1 graphically depicts the surface-water discharges and their sizes in Nebraska. However, this fIgure must be used with caution in assessing amounts of surface water that might be available for supple- mental use. Much more detailed analysis of several factors is required before reliable supplies of available supplemental water can be determined. Examples rn- clude the North Platte. loup, and Republican drainage basins. The discharges that are shown on the map for these basins already may be appropriated to lower reaches oltMe basrns or adJacent lower basins. Appen- diX A. "Water Supplies in Nebraska Streams," presents 3.,