Palouse Internal Tide Gate Uplift Design

Palouse Slough drains into Haynes Inlet in the Coos basin and is one of the highest producing coho anchor habitat streams on the Oregon Coast. The lower Palouse basin has a primary gate and multiple internal tide gates that protect the upstream properties from tidal inundation and restrict fish access to critical floodplain rearing habitats. CoosWA has partnered with the Haynes Drainage District to upgrade the primary tide gate, the next step is addressing the internal gates and their associated properties. One of the internal gate upgrades will improve passage and flow conveyance to roughly a mile of stream and nearly 50 acres of seasonal rearing habitat below 3 ft in elevation. Past management practices have degraded rearing habitat upstream due to disconnected floodplains and habitats, choked channels from sedimentation and vegetation, and undersized crossings. An ill-set internal gate has allowed higher stream flows to bypass the property’s tide gate and flow directly onto a neighboring property and out a separate tide gate, which has caused massive erosion between properties, further degrading water quality and potentially stranding fish. This proposed project seeks to address floodplain and habitat connectivity, fish passage, instream complexity and water quality to improve critical off-channel rearing habitat upstream of this internal tide gate to fully expand the benefits of both the primary and internal gate upgrades, while also addressing the unwanted hydrologic connection between the neighboring properties to ensure the proper function of the upgraded tidal infrastructure. CoosWA will continue to work with the established Palouse technical team and the private landowner on this uplift design to ensure it functions with the primary and internal gate upgrades.

Ecological uplift upstream of the future upgraded tidal infrastructure on the lower Palouse Slough is the critical next phase to further expand the foundation improvements made by the primary Palouse tide gate upgrade to the hydrology and fish passage to the entire Palouse basin. The goal of this project is to complete the design and permitting necessary to improve fish passage, habitat connectivity, water quality, and productivity to critical off-channel tidal rearing habitats in a 100-acre parcel in lower Palouse basin that is behind an internal tide gate. This proposed project will design the ecological uplift necessary to fully capture the benefits of the upgraded tidal infrastructure throughout lower Palouse. The proposed project area is the largest area upstream of an internal gate in Palouse with nearly 100 acres of lowland pasture and a mile of stream; however, the habitat quality is very degraded. This project seeks to improve habitat connectivity, floodplain connectivity, fish passage, instream complexity, riparian vegetation/in-stream woody debris, water quality, and productivity of critical off-channel tidal rearing habitats in the lower Palouse basin.

This project will address the degraded quality of off-channel rearing habitat and floodplain connectivity in the Palouse subbasin. Tidal floodplains are crucial for overwintering coho salmon but have been severely diminished by past land management practices that drained wetlands for agriculture. The proposed project area has roughly 50 acres below a 3-ft elevation with numerous disconnected swales and seeps with no egress back to the main channel. By restoring channel networks and floodplain connection, the project will improve instream habitat and sediment transport, reduce weed growth, and create cooler, more oxygenated water while also improving seasonal ingress and egress to critical overwintering habitat. This will greatly improve the habitat and water quality upstream of the internal tide gate as well as lower Palouse and Haynes Inlet which will benefit salmonids, oysters, eelgrass, and other aquatic species, promoting ecological and economic resilience in the Coos basin.