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<br />Future Condition - No Additional Ground-water Development <br /> <br />The total irrigated acreages in the Upper Pl atte River Basin have <br />increased substantially in the last several years, especially in the <br />Nebraska portion. Most of this development has been the result of <br />drilling wells and pumping ground water. Not all ground-water develop- <br />ment would directly affect the surface flows, thus, a finite difference <br />model was used to simul ate the approximate effects of Nebraska ground- <br />water irrigation development on the flows of the Platte. The area of <br />influence contained in the model includes about 4.3 million irrigable <br />acres of which 3.5 million are in the Platte River Basin and 0.8 million <br />are in the Blue River Basin. This is the same irrigable acreage that <br />was used in the Platte Level B Study. <br /> <br />Under 1977-present conditions it is estimated that 1.4 million acres are <br />irrigated from ground water in the modeled area (0.9 mi 11 ion and <br />0.5 million acres in the Platte and Blue River Basins, respectively). <br />The estimate is based on well registration data from the Nebraska <br />Agricultural Statistics and canal irrigated acreage data from the <br />Nebraska Department of Water Resources. <br /> <br />An alternative future has been generated which reflects the present <br />condition modified by Grayrocks and includes the estimated impact <br />of the 1977 level of ground-water development projected 50 years into <br />the future. Table 13 illustrates the monthly flows under this alterna- <br />tive future. <br /> <br />Assuming that no additional ground-water development occurs after 1977, <br />streifllflow depletions in the year 2027 would be 312,000 acre-feet per <br />year, or 127,000 acre-feet per year greater than at present. Depletion <br />of ground-water storage would still be occurring but at a lesser rate of <br />403,000 acre-feet per year. An additional 67,000 acres of subirrigated <br />land would be lost which would result in a total annual saving of some <br />328,000 acre-feet per year. <br /> <br />The greatest change in monthly flow condition can be observed at the <br />four points on the mainstem PI atte River in Nebraska. Even with no <br />increase in ground-water irrigation development in the Nebraska portion <br />of the study area, the model shows that over a 50-year period, flows in <br />the Platte would decrease on an annual basis from about 5 to 10 percent <br />through the reach used by the migratory birds. Thus, the present <br />acreage irrigated by ground-water within the PI atte Basin of Nebraska, <br />would have substantial impacts on future surface hydrologic conditions. <br /> <br />52 <br />