OREGON WATER SCIENCE CENTER HYDROLOGIC STUDIES
Umatilla Basin Ground-Water Study
Water management in the arid Umatilla Basin has become increasingly complex in recent years. Competing demands from society for generating hydro-electric power, maintaining and restoring fisheries, restoring watershed health, providing water for growing communities, and increasing agricultural production through irrigation, have put water resources in the Umatilla Basin and throughout the northwest, under increasing pressure. Management of water resources requires a sound scientific basis so that “optimal” solutions can be identified that satisfy as many of the societal demands as possible.
Among the many entities having interests in the water resources of the basin are the Cities of Hermiston and Pendleton, irrigation districts, the Confederated Tribes of the Umatilla Reservation, Umatilla Basin Watershed Council, Umatilla Soil and Water Conservation District, Umatilla and Morrow County Planning Departments, Bureau of Reclamation, Oregon Water Resources Department Oregon Department of Environmental Quality, U.S. Army Corps of Engineers and Bonneville Power Administration. With so many agencies responsible for such a wide range of interests in the basin, it is critical to have a common basis of scientific understanding of the resource to facilitate the process of finding cost-effective solutions that meet the societal needs.
Several water-management issues in the Umatilla Basin point out the need for a more comprehensive understanding of the hydrologic system. An understanding is needed that clarifies the relations between ground-water withdrawals and streamflow, between precipitation and ground-water recharge, and between irrigation practices, recharge, and return flow. Most importantly, a quantitative understanding is needed that will support integrated solutions to problems involving water availability and water quality. Examples of issues currently facing water managers and planners in the basin are: (1) long-term water-level declines in basalt aquifers that have historically been tapped for irrigation and municipal supplies, (2) the effects of distribution of irrigation water in the lower basin on return flows to the Umatilla River, (3) high nitrate concentrations in ground water in the lower basin, and (4) the effects of new ground-water development on flows in the Umatilla River and other streams during the summer and fall low-flow periods.
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