Ongoing stability issues at the Willamette Falls Fishway left some areas in danger of failure and thus in critical need of repairs. An engineering investigation and study was initiated to determine the existing operating conditions and causes of the structural deficiencies. PSE was brought in to conduct a structural evaluation, followed by the design of rehabilitation and repair program. Initial emergency, temporary repairs were designed and installed before the high-water season to mitigate the risk of complete structural failure. For a subsequent period spanning several years, data recorders were installed to track movements of the structure through changing river and climatic conditions in order to help determine the causal actions for the damage. Without this important data, any repair procedure may have resulted in subsequent deterioration and damage, again putting the structure at risk, as well as an inefficient allocation of repair funds.
Following analysis of the collected data, PSE completed the design of the permanent repairs; this was compromised of several reinforced concrete foundations as well as Fishway entrance repairs. PSE’s repair plan combined a series of foundation support elements plus thermal force return tension rods to stabilize the structure and arrest the thermal actions inflicting damage to the structure. The remediation approach employed by PSE – installing pretensioned return force rods to a monolithic fishway structure – proved to be both effective and unique. Willamette Falls Fishway is a highly sensitive environmental location, and it presented some challenging conditions for the successful construction of the much-needed repairs. These challenges included the necessity to limit total shutdown of the fishway during repairs. While the in-water work period is typically limited to four months, a shorter work window was targeted for the project in order to have minimal impact on sensitive fish populations. The newly repaired fishway was completed within the expedited schedule, such that the facility could be reopened in the fall, ensuring the successful upstream migration of hatchery summer fish. PSE is proud to have contributed to the Department of Fish and Wildlife’s mission to protect and enhance fish and wildlife and their habitats for use and enjoyment by present and future generations.