Tidegate Pipe Sizing Tool - Alternatives Analysis

This project addressed a component of a coast-wide problem: failing tide gate infrastructure that has a negative impact on natural resources and local economies. Additionally, current tide gates are barriers for fish to highly productive habitats. There is a need to replace tide gates that meet fish passage criteria while also still protecting land for other uses. Replacements can be time consuming and costly. The Tide Gate Partnership identified that funding constraints and the design/permitting process are major factors contributing to this challenge. This project completed the initial phases to develop an engineering tool that can size the culvert for a tide gate with simple, easy to obtain model inputs. This tool will assist in streamlining the design and permitting process and reducing the costs associated with tide gate upgrades. The outcome of this work will be a user friendly tool. The alternatives analysis listed each alternative and covered the methods employed, provided assumptions of each individual method, summarized tool inputs, outputs and interface process, and discussed feasibility for each alternative. The preferred alternative has been selected as a final outcome of this grant and a future grant will be sought to complete the tool development. Key partners include: NMFS, ODFW, CoosWA, and engineering firm: Northwest Hydraulic Consultants.

This technical assistance grant will benefit salmon, steelhead and other native fish by starting the initial phase of developing a tool that will assist in streamlining the design and permitting of tidegate replacement. Specifically, the tool will identify the size of the culvert necessary to meet state and federal fish passage standards with a tidegate. Along the Oregon Coast and Columbia Estuary, failing tidegates are currently limiting fish access to critical slow-water refugia, rearing habitat and spawning habitat. Lack of access to winter rearing habitat is the primary limiting factor for ESA-listed Oregon Coast coho (NMFS Coho Recovery Plan 2016). Coho and other anadromous fish use tidal habitats for feeding, rearing and as a source of slow water refugia during high winter flows. Studies have shown smolt growth rates are often 1.5-2.0 times greater for off-channel and tidal wetland habitats compared to stream locations (Nickelson 2012, ODFW, unpublished 2014). Nickelson (2007) estimated that these types of habitats historically were capable of rearing sufficient number of coho juveniles to produce 11-17 returning coho adults for every acre of high functioning floodplain wetland. Overall, this grant will promote the recovery of salmon and steelhead by streamlining tidegate replacements with upgrades that improve fish passage to critical habitats.