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<br />r.;l:ti~h <br /> <br />Although the South Plalle River and North Platte <br />River drainage basins are about the same size. the <br />amount of water entering the state via the North Platte <br />River or canals at the Nebraska-Wyoming slale line <br />averages about'.5 million acre-feel annually while only <br />slightly more than 300.000 acre-feet annually comes <br />Into the state through the Soulh Platte Alver at the <br />Nebraska-Colorado state Ime Nebraska benefits in- <br />directly from water Imported Into the South Platte River <br />basin from the Colorado River and the North Platte <br />River basins In recent years such ImportatIOns have <br />amounted to about 300,000 acre-feel annually. <br />Although thiS amount apprOXimates the amount enter. <br />Ing Nebraska, most of the Imported water IS used con. <br />sumptively in Colorado Natural flows. Irrigation return <br />flow and other sources provide the water that enters <br />Nebraska. Natural evapotranspiration losses are large <br />in the South Platte River drainage baSin in Colorado <br />where consumptive use through Irrigation IS relatively <br />high. <br />Of the remaining 2 million acre. feet of stream flow <br />entenng the state. about 100.000 acre-Ieet enters the <br />state from other streams onginating in Kansas, South <br />Dakota. Colorado. and Wyoming. The flow into the state <br />from the Republican River and the Niobrara River and <br />their tributaries constitutes most of the remainder (Sen- <br />tall and Shatter, t979) Flows are further discussed 10 <br />Chapter 3 and Appendix A of this report <br />Water in streams can be considered supplemental <br />water especially 10 the losing reaches 01 streams. Most <br />streams In Nebraska are groundwater dralOs, not <br />sources of groundwater recharge. and overland runoff <br />is a major component of flow PubliC water supply and <br />irrigation wells do tap groundwater reservOirs adjacent <br />to the few losing reaches 01 streams. In most of these <br />cases. the streams do not provide significantly different <br />amounts of annual recharge under conditions of con- <br />tinUOUS flow or interrupted flow. Some streams of small <br />annual discharge on the semi-arid plains of western <br />Nebraska are probably except!ons to this generality. <br />Where sublrrigated lands are adjacent to streams, the <br />water.level under these lands ordlOarlly IS malOtained <br />by groundwater moving toward or parellel to the stream <br />and not be seepage away from It. On a statewide baSIS. <br />then, the seepage from streams as a source of ground. <br />water recharge or supplemental supply IS Quite small <br />and probably cannot be IOcreased by any great signifi- <br />cant amount. <br />The water stored 10 or the water added to the state's <br />groundwater reservOIr is the largest potential source <br />of water available for supplemental use in the state. The <br />supply ;s estimated to be more than 2 billion acre-feet <br />of good quality water (Engberg and Spaid 109. 1978) at <br />relallvely shallow depths. This is discussed lurther 10 <br />Chapters 2 and 3 of this report and 10 the Policy Issue <br />Study on Groundwater Reservoir Management <br />(Nebraska Natural Resources CommiSSion, 1982). like <br />precipitation. streamflow and stored surface water. <br />groundwater is not evenly distributed wlthlO the state <br /> <br />or WlthlO any region. Geologic conditions have naturally <br />limited the occurrence and availability of groundwater <br />around me northern and southern margins of the state <br />and In tile glaCiated eastern part of the stale. <br />The amount 01 groundwater stored in different areas <br />of the state has been changed because 01 water use. <br />These changes. which are the results of groundwater <br />Withdrawal by wells and surface-water storage and <br />distribution, have been documented by observation- <br />well mOnlloring in a cooperative program 01 the U.S. <br />Geological Survey and the Conservation and Survey <br />DiviSion. IANR. UN-l since t930. Many other federal. <br />state, and local agencies have contributed data and <br />resources to the program. Reports containing maps <br />depicting progresSive Changes in water levels have <br />been prepared SlOce 1963 and are now published an- <br />nually (Johnson and Pederson, 1982). Although <br />changed in geographical dIstribution, the total amount <br />of groundwater In storage within the state has <br />Changed hUle Since the first settlers arrived. <br />Awareness of Nebraska's large store of the available <br />groundwater developed slowly. Awareness of the op- <br />portunity to use the storage capacity 01 the <br />underground and to Integrate that storage with surface- <br />water storage for various uses will await general <br />recognition by the public. <br /> <br />E. USES OF SUPPLEMENTAL WATER <br />SUPPLIES <br /> <br />Irrigation has been and will continue to be the largest <br />user of water In the state. The vagary of the climate <br />was recognized In accounts 01 the early explorers and <br />settlers and has been documented by more than 100 <br />years of weather records. This condition requires sup- <br />plemental water for sustained crop production In most <br />ollhe state. Groundwater is the largest source of water <br />used for irrigation in Nebraska_ Although, as defined <br /> <br /> <br />/" <br /> <br />,.5 <br />