Wallowa Lake Dam Design Build Rehabilitation

Natural Resources
Alternative delivery (D-B, progressive D-B, CM/GC, CMAR, EPC), Professional services, Construction, Construction management, Program management (owner’s engineer/representative), On-call (MSA, IDIQ, MATOC)
Joseph, OR
Wallowa Lake Irrigation District
why it matters

In 2017 Wallowa Lake Irrigation District has been working towards its goals, with the assistance of State funding, to provide rehabilitation to the Wallowa Lake Dam. McMillen has been supporting this project for more than a decade to provide services to improve water conservation, fish and wildlife habitat, agricultural water supply deliveries, potable drinking water, flood protection, and recreation opportunities. The project focuses on dam safety and fish passage components, but also considers the needs of the community and irrigation systems downstream of the dam. The project enhances and supports downstream fish and wildlife stakeholders by identifying and mitigating water conveyance issues and providing water savings benefits.

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Since 1996, McMillen has provided planning and engineering services and developed a long-term funding program using state, federal, and local funding sources to provide multiphase project implementation. We are currently serving as the design-build lead to rehabilitate the existing dam. The project scope includes a detailed condition assessment and destructive testing of the existing concrete to determine its strength. This analysis and an updated probable maximum flood study determined that rehabilitating the existing dam would be the most cost-effective option. The dam modifications will involve adding new concrete to enhance stability, installing new outlet conduit liners and gates, constructing a new gate spillway, and encasing the entire dam structure in a reinforced concrete shell. Additionally, fish passage facilities will be constructed upstream and downstream of the dam. We also investigated opportunities to incorporate hydroelectric generation.

McMillen has been involved in dam safety inspections and planning for long-term improvements to the dam. We conducted a feasibility study to determine the best approach to address significant dam safety issues and have been conducting periodic dam safety inspections in collaboration with the Oregon Dam Safety Engineer. McMillen has also assisted in updating emergency action plans and O&M plans.

One project challenge was determining the best approach for fish passage. Initially, a volitional fish ladder was considered, but it was deemed unfeasible due to the reservoir's operation as an irrigation and flood control facility. McMillen developed alternatives and facilitated design and planning charrettes with agencies and tribes. Ultimately, the trap and haul alternative was selected, along with approved design criteria and operational considerations. McMillen's expertise and collaborative approach were instrumental in reaching this solution.

McMillen has worked closely with numerous stakeholders and federal, state, and local agencies to ensure their needs and requirements are met. We have established a memorandum of agreement between key stakeholders, demonstrating our commitment to addressing the community and basin-wide needs tied to irrigation systems.


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