Geology, wells, pumping contribute to groundwater level declines
Geologic barriers, the intermixing of water between aquifers through wells, and groundwater pumping contribute to the pattern of declines of groundwater levels in the Columbia Plateau, according to a report published by the U.S. Geological Survey.
Groundwater from the 44,000-sq-mile Columbia Plateau Regional Aquifer, a system in decline since the 1970s, is a critical resource for the nearly 1.3 million people in Idaho, Oregon and Washington. It also provides irrigation water for the region’s estimated $6-billion-per-year agriculture industry.
To help resource managers in the region, the USGS Groundwater Resources Program began a study in 2007 of the Columbia Plateau Regional Aquifer System to answer key questions about widespread water-level declines, reductions in groundwater flow into rivers and the as-yet unknown effects of a changing climate on groundwater resources.
As part of this effort to document changes in the aquifer system, scientists compiled water levels measured in about 60,000 wells over the last 100 years. From a subset of the collected information, scientists developed a groundwater-level trend map for a period of widespread groundwater level changes (1968 to 2009). The average rate of change for all wells was 1.9 ft per year of decline, with 72% of all wells declining.
Scientists also analyzed water-level data to define areas of similar groundwater flow conditions. The areas of focus for this analysis included two large areas of continued concern for locals and state agencies: the Umatilla area, Ore., and the Palouse Slope/eastern Yakima Fold Belt in the Columbia Basin Ground Water Management Area (GWMA) consisting of Adams, Franklin, Grant and Lincoln Counties, Wash. Scientists found that in these areas groundwater levels have declined hundreds of feet and that geologic barriers to groundwater flow protect some areas from decline while making declines in other areas more severe. Evidence suggests that both groundwater pumping and leakage of groundwater between aquifers through long open intervals in wells may be contributing to the observed groundwater level changes.
Information gathered in the study was used to identify groundwater flow paths and major barriers to groundwater flow. Understanding the features that control the direction of flow will help scientists build a groundwater flow simulation model that water managers can use to test ways of managing the region’s groundwater under different development and climate conditions.
Agencies cooperating in the collection of groundwater data used in the Columbia Plateau Regional Aquifer study: Columbia Basin Ground Water Management Area, Confederated Tribes of the Umatilla Indian Reservation, Oregon Water Resources Department, U.S. Department of Energy, Walla Walla Basin Watershed Council and Washington State Department of Ecology. Click here for more information about the study.