The groundwater study area will include the entire Fifteenmile Creek watershed. Groundwater levels in the basalt rock layers beneath this area in north-central Oregon have been declining since the 1990s. Several wells have dropped so much that they meet the State’s definition of “excessive decline.” Surface water in the area is also overallocated. Over the past 20 years, Fifteenmile Creek has had very low water levels, and in some years parts of the lower creek have dried up.
Even though these problems are well known, it is still unclear what causes are most responsible. Potential causes include increased groundwater pumping, climate-driven reductions in baseflow and recharge, increases in riparian evapotranspiration and other hydrologic processes. A comprehensive study in this area is needed to characterize the hydrologic system and provide the scientific foundation for future water-policy and management decisions.
The study will help develop a comprehensive understanding of the groundwater system and its interactions with surface water in the Fifteenmile Creek watershed by:
- Developing a foundational conceptual groundwater model that integrates existing and new data to describe hydrostratigraphy, groundwater-flow directions, and zones of recharge and discharge, including groundwater/surface-water interactions;
- Evaluating causes of groundwater-level declines in CRBG aquifers, including groundwater pumping, inter-aquifer commingling wells, and climate-related changes in recharge; and
- Assessing subsurface contributions to periodic stream desiccation and low flows in Fifteenmile and Eightmile Creeks, including stream/well hydraulic connections, structural/stratigraphic groundwater flow barriers, riparian evapotranspiration losses, and climate-driven declines in baseflows.
There are a number of ways to be involved in helping address these declines and meeting future water needs, which include:
Participate in data gathering efforts - Department staff are working with water users to gather water level and water use data. Understanding the groundwater flow system and the water balance is the first step toward making decisions about future water management. If you have not met with Department staff regarding well measurement, you are encouraged to speak with staff at the meetings.
Local discussions - The Department is planning a series of community meetings throughout the study. Please sign up for GovDelivery Announcements for more information about upcoming meetings.