Big Creek Dam 30% design estimates ~$185 million; staff pauses 60% work pending studies

Newport City staff and HDR consultants presented a 30% design update for the Big Creek Dam replacement project at a council work session, saying new geotechnical and seismic findings and material cost increases have pushed the project's total project estimate to about $185 million. Verena Winter, project manager for HDR, led the presentation and warned that technical challenges are translating directly into higher costs.

The update matters because the Big Creek reservoirs are the city's only drinking water source and both dams are classified by the Oregon Water Resources Department Office of Dam Safety as 'potentially unsafe' (the upper dam is classified as unsafe), the consultants noted. Winter said the classification and seismic risk are driving design choices; Adam Toothman, HDR's structural engineer and engineer of record, described a roller‑compacted concrete dam chosen because concrete has historically performed better in high seismic areas.

The consultants said the 30% package includes major project components: dam cross sections, intake and outlet layouts, temporary and permanent access roads, stream restoration upstream to the treatment plant, and a revised cost estimate based on the 30% design. Winter said the package delivered to the city in January included roughly 150 drawings and supporting reports outlining assumptions and analyses.

Cost and contingencies. HDR's updated accounting separates a hypothetical construction contract from additional contingencies and non‑contract costs. The firm's 30% estimate produced a notional construction contract amount of about $122 million; after adding a design contingency (10%) and a procurement/contract strategy allowance (5%), HDR presented a construction award estimate near $140…