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1 <br />EXECUTIVE SUMMARY <br />THE ISSUE: HIGH GROUND WATER LEVELS <br />Many areas in the Central Platte Valley in Nebraska have been experiencing high ground <br />water levels for several years, causing problems with waterlogged farm fields and <br />flooded basements. Some local land owners are concerned that additional flows <br />generated by the Endangered Species Recovery Program (Program) water management <br />will cause existing problems to become worse. <br />ANALYSIS OF INTERRELATED FACTORS <br />To determine the range of potential effects from the Program's proposed environmental <br />water account, Reclamation analyzed the relationships of ground water levels, river <br />flows, and precipitation. Our major findings were: <br />Topography.— Aquifer recharge from precipitation in central Nebraska is relatively high <br />due to the generally flat terrain and the sandy soil textures. <br />• Because ground water moves slowly, river rises and adjacent ground water level <br />rises are not simultaneous if the ground water level is responding to a change in the <br />river. Thus, when ground water levels rise at the same time as the river rises, a third <br />factor (e.g., precipitation) must be involved. <br />Executive Summary <br />Geology and soils.— The aquifer is highly permeable and has positive connection to the <br />Platte River (meaning ground water can flow easily between the aquifer and the river). <br />Climate.— Precipitation has been much above normal since 1980, which contributes to <br />water tables that are higher than they have been since the 1950s (the onset of extensive <br />irrigation pumping) and water levels are generally rising. <br />Irrigation.— Irrigation from river diversions has raised the water table within the <br />irrigated areas and near canals and reservoirs. Irrigation by wells has tended to lower <br />water tables or at least reduce the flow toward the river. <br />River levels <br />• River levels have an influence on ground water levels near the river. At distances <br />more than a few thousand feet from the river, the water table elevation is generally <br />several feet higher than the river and thus does not react to river levels. <br />• Because ground water moves slowly, river rises and adjacent ground water level <br />rises are not simultaneous if the ground water level is responding to a change in the <br />river. Thus, when ground water levels rise at the same time as the river rises, a third <br />factor (e.g., precipitation) must be involved. <br />Executive Summary <br />