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<br />2-20 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />,I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Ground water containing concentrations of total dissolved solids exceeding <br />2,000 miligrams/liter, considered very poor quality, is found in highly <br />developed aquifers in eastern Montana, central South Dakota, western Iowa, and <br /> <br />northwestern Missouri. <br /> <br />Interrelationship of Surface a~d Ground Water <br />With increasing development of both surface and ground-water resources, <br />their hydrologic interrelationship is becoming increasingly more important to <br />users. Several types of effects have resulted from public and private water <br />and land resource developments. One of the most significant effects occurring <br /> <br /> <br />in certain areas of the Missouri Basin has been the reduction of inflow to the <br /> <br /> <br />surface system caused by withdrawals of associated ground water. Ground-water <br /> <br /> <br />pumping for sprinkler irrigation is diminishing streamflows otherwise available <br />for instream and offstream uses in parts of Colorado, Kansas, and Nebraska. <br /> <br /> <br />Other notable effects of development occurring within the basin include <br /> <br /> <br />alteration of runoff and infiltration caused by changes in land use and <br /> <br /> <br />management, such as conversion of grassland to cropland, and increased aquifer <br /> <br />recharge due to surface water storage. <br /> <br />Existing Major Water Resources Development <br />Initial water resources developments in the Missouri River Basin, <br /> <br />beginning more than 100 years ago, were earthen structures built on smaller <br /> <br />streams to meet single-purpose needs, primarily water supply. Since the <br />1930's, surface-water developments have often been supplemented with <br />ground-water development, particularly for privately developed irrigation on <br />the plains of Colorado, Kansas, and Nebraska. <br /> <br />In the past 40 years, a number of major reservoirs have been constructed <br /> <br />in the basin. Most of these projects were built to serve multiple purposes and <br />