The Columbia River Basin in Washington, Oregon, and Idaho supports a $5 billion/year agricultural industry, leading the nation in production of apples and nine other commodities. Ground-water availability in the Columbia River basalts and the basin-fill sediments of the Columbia Plateau Regional Aquifer System (CPRAS) is a critical water-resource management issue in the Basin where the water demand for agriculture, economic development, and ecological needs is high. Ground-water availability is a primary consideration for balancing the conjunctive use of surface-water and groundwater supplies throughout the CPRAS.
Ground-water pumping from the Columbia River basalts has resulted in more than 300 ft of water-level declines in some areas of the aquifer system, placing important agricultural sectors at risk. Ground-water depletion also has contributed to adverse environmental impacts. Declining groundwater levels have significantly reduced stream flows and have contributed to loss of wetlands and degradation of aquatic habitat. Current streamflow in many subbasins is inadequate for certain fish listed under the Endangered Species Act. Conversely, in some areas of the CPRAS excess recharge from surface-water irrigation over the past century has resulted in additional ground water in both the sediments and basalts that is potentially available for use. The excess 'artificial' recharge has created wetlands now dependent on continued irrigation, and has contributed to landslides and excess sediment loads in the Columbia River at the Hanford Reach National Monument.
