Eldon Mills Dam Raise (Barney Reservoir)
Eldon Mills Dam and the Barney Reservoir are located at the headwaters of the North Fork Trask River in Oregon's northern Coast Range. The earth and rockfill embankment diverts water eastward into the water supply system for municipalities in the Tualatin Valley. Water demands in the valley created a need for increased output from the reservoir. Cornforth Consultants was retained by the Cities of Hillsboro, Beaverton, Forest Grove, the Tualatin Valley Water District, and Clean Water Services as the Prime consultant to perform studies to raise the dam.
Cornforth Consultants investigated various conceptual options, and recommended an earth and rockfill design that raised the existing dam's height from 72 to 131 feet and increased the reservoir's storage capacity from 4,000 to 20,000 acre-feet. Preliminary design tasks included evaluation of seismic hazards in the region (including the Cascadia Subduction Zone), geologic reconnaissance, 67 exploratory borings, groundwater investigations, geophysical explorations, hydraulic pressure testing and borrow source studies.
Final design analyses included static and seismic stability, evaluation of seepage beneath and through the dam, laboratory testing of foundation and embankment materials, settlement and quantities. In addition, Cornforth Consultants developed the Engineer's construction cost estimate, provided construction sequencing over several seasons, evaluated constructability, provided construction plans and specifications, and coordinated the bidding and awarding of the contract. Quality Assurance/Quality Control was provided during the 4-year construction period.