Long-Term Ground-Water Declines
Declining ground-water levels were documented locally in the Willamette Valley as early as the 1960s. Water-level declines cause serious water supply-problems and hardship for rural home owners as well as for municipalities and irrigators, and threaten the long-term sustainability of the resource. The Willamette Basin Report lists 8 areas with existing water-level decline problems and 4 with potential decline problems. Of these 12 areas, all but one involve aquifers within the Columbia River Basalt Group. The basalt aquifer is the principal or sole aquifer in uplands within and surrounding the Willamette Valley, and beneath basin-filling sediments in certain areas in the valley. Because of similar hydrogeologic conditions, the sustainability of ground-water supplies from all Columbia River Basalt Group aquifers in the basin is of concern.
The Willamette Basin Report proposes a policy to "prevent excessive water-level declines and restore aquifer stability while preserving limited storage for priority uses in the vicinity." Significant efforts have been made by OWRD staff over the years to collect water-level data and geologic information in some of the basalt areas in the basin and these efforts have led to a general, qualitative understanding of basalt hydrology has been developed. However, many aspects of basalt hydrology are still poorly understood, such as structural controls on ground-water flow, recharge mechanisms and rates, the nature of ground-water flow between water-bearing units, and details of the head distribution. Knowledge of all these hydrologic characteristics is necessary for effectively managing development and use of basalt aquifers, including well construction.
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Last modified: Mon Jan 29 13:46:16 1996