The Fifteenmile Watershed Council and the Wasco County SWCD completed an aboveground storage feasibility study in 2015 (AP and GSI, 2015) to evaluate the potential for developing an off-channel surface reservoir to supply water to irrigators with senior surface water rights in exchange for not diverting live flow from the creek during the summer months. The above ground storage study identified three potential reservoir sites in side-drainage's south of Fifteenmile Creek, concluding that an off-channel reservoir that would store approximately , acre-feet (AF) to exchange with senior water rights holders is feasible for a cost of over $13 million. For the purposes of evaluating project benefits, the study assumed the project would result in an additional 5 cubic feet per second (cfs) of flow to Fifteenmile Creek over a period of 160 days.
The conclusion of the aboveground storage feasibility study provided alternatives that may be more feasible. One of those alternatives was a subsurface storage option. The council chose to move forward with exploring this underground storage project and hired GSI, GeoSystems Analysis, and Anderson Perry to conduct a Subsurface Feasibility Study. The study evaluated subsurface concepts that would involve diverting and treating water from Fifteenmile Creek using riverbank
filtration (horizontal or vertical wells), or an infiltration basin, storing the water in a Columbia River Basalt Aquifer, and then using the water to enhance Fifteenmile Creek flows during the summer/fall low flow period by two possible methods:
Exchange: Similar to the aboveground storage concept, the subsurface storage concept would store water during higher flow periods and deliver water to irrigators with senior surface water rights upstream of Dufur in exchange for
not diverting water during low flow periods.
Replacement: The replacement concept would involve storing water during
higher flow periods and returning the stored water directly back to the creek
during low flow periods.
At the conclusion of the managed underground storage feasibility study, no fatal flaws were found in the replacement concept. The Fifteenmile Watershed Council is moving forward with an Aquifer Storage and Recovery Project and are taking the next steps toward a pilot study. A small-scale infiltration facility is needed in order to investigate soil aquifer infiltration effectiveness and address the likely recharge season and address any uncertainties regarding system size and design parameters before a full scale facility is constructed. The council has been working with contractors GSI Water Solutions and GeoSystems Analysis to dig test pits at various locations in the Dufur Valley to ground truth the area and explore these aquifers.
There have been 25 test pits, 3 alluvial aquifer test wells, 6 cylinder infiltrometer tests, and laboratory physical/hydraulic testing completed. Through these tests, locations have been narrowed down to 3 potential sites.
In the coming weeks the contractors will be evaluating the potential site locations and providing a summary of their findings at the next watershed council meeting scheduled for September 10th at 6:00pm at the Barlow Ranger Station in Dufur.
Project photos are below and council presentations
along with Feasibility Reports are to the right.
Subsurface Storage Feasibility Study Final Report
Above Ground Storage Feasibility Study Final Report
Thanks to the generous funding from our partners at OWRD and OWEB the Managed Underground Storage Feasibility Study has been completed. The Watershed Council and SWCD are taking the next steps to develop a pilot project for the selected location. The final Technical Memo from GSI Water Solutions, GeoSystems Analysis and Anderson Perry, can be found below.