Tillamook River Wetlands: Engineering and Design

The Tillamook River Wetlands (TRW) project focused on building a strong and clear case for the preferred alternative for restoring tidal and floodplain processes to the historical tidal channels and wetlands at TRW, while maintaining roadway access between Highway 131 and Tillamook River Road/Highway 101. Because restoration actions are inextricably linked to the removal or upgrades to the failing Burton-Fraser Road (BFR), this project included a detailed Roadway Alternatives Comparison and Cost-Benefit Analysis Report to evaluate two alternatives. Alt 1: reconnect TRW to the Tillamook River with multiple new bridges and culverts, and Alt 2: remove a portion of BFR to maximize TRW reconnection and restoration, while upgrading the nearby Eckloff Road to maintain the important county route (a primary emergency ingress/egress route to three coastal communities). This project culminated in a 60% Design Plan Set and Basis of Design Report with estimated construction costs. Supporting design and analysis included potential setback dike locations, options for restoring the historical condition of the south bank of the Tillamook River including the connection to an adjacent remnant tidal forested spruce swamp, 2D hydraulic modeling and fish passage tide gate analysis, and considerations for maintaining access to three private properties.

The Tillamook Bay estuary is one of the most productive estuaries on the Oregon Coast and supports one of the most prolific salmon fisheries in the state (Knutsen, 2017). An Oregon Department of Fish & Wildlife (ODFW) survey conducted in the 1970’s identified 56 species of fish that use the estuary at various times of the year (Ellis, 2000), including eight salmonid species. TRW’s primary contribution to Tillamook Bay’s salmonid populations will be increased access to and a net increase in highly productive juvenile rearing habitat. It is of note, two of TRW’s tide gates no longer have doors and are likely allowing salmonids limited access to the sites wetlands currently.
Of primary importance for TRW is the Oregon Coast Coho salmon, a federally threatened Evolutionary Significant Unit (ESU) of Coho salmon. NOAA’s recently released Recovery Plan for this species states the following in regard to successful Coho recovery: “the primary focus is to protect and restore freshwater and estuarine rearing habitats upon which egg-to-smolt survival, and overall productivity, depends, so the highest priorities are for strategies and actions related to rearing habitats”. In other words, rearing habitat is a primary limiting factor for Coho, and conservation and restoration of properties that support such habitats is critical to their recovery. This determination was based on observations that while there have been large fluctuations in adult spawners since the year 2000, the number of smolts produced has stayed relatively the same leading to the determination that rearing habitat is limiting. Additionally, Tillamook Bay is legally designated as critical habitat for the ESU (NOAA, 2016). TRW provides a relatively rare opportunity to acquire private land in order to connect and restore tidal wetland rearing habitat.
TRW will acquire and restore 73 acres of tidal wetland rearing habitat in the heart of Coho distribution in Tillamook Bay. To estimate the potential benefit to Coho rearing this project will have, we can turn to modeling that took place for tidal wetlands one mile downstream of TRW. Bio-Surveys Inc. modeled the effects of restoring approximately 21 acres of Esther and Fagan Creek wetlands based on empirical data collected during juvenile Coho surveys. Bio-Surveys determined that the Coho rearing potential of these wetlands is 51,000 fish or 1.67 fish/square meter (Demeter, 2009). If we extrapolate this number to TRW, TRW will provide potential rearing opportunities to 177,286 juvenile Coho salmon annually. TRW will move the needle for Tillamook Bay’s threatened Coho population and will most certainly benefit the estuaries’ other salmonid populations as well.
It is also important to note, that while this question, and a lot of Oregon’s recovery focus is centered on salmon, it shouldn’t be overlooked that there are a number of other estuarine dependent fish and other wildlife species that will benefit directly or indirectly from the acquisition and restoration of TRW. These benefits will occur via reconnection of lost wetland habitat, enhanced structural complexity, removal of exotic species, forage enhancement, and water quality improvements. Ensuring a complete, biodiverse, and multi-trophic species assemblage is restored at TRW will certainly benefit salmon, but will include a myriad of other species benefits. Please see the supporting documents section for a list of other special status and ecologically important species that will benefit from TRW.
This technical assistance proposal will complete site characterization and opportunities anlysis begun in Phase I and develop final engineering designs, construction specifications, cost estimates, and permit documentation to acquire necessary permits, restoration funding, and implement restoration of the 73-acre “Tillamook River Wetlands” project site.