Corps Report Recommends Removing 550-Foot Yakima River Delta Causeway Creating Warm Water, Increased Predation On ESA-Listed Salmon
The U.S. Army Corps of Engineers, Walla Walla District has released the results of its Yakima Delta ecological restoration feasibility report, recommending the removal of a causeway to improve conditions for salmon in the Yakima River Delta.
The delta’s Bateman Island — located in Richland, Washington at the confluence of the Yakima and Columbia river — is only accessible via the causeway on its south side. The causeway completely blocks water flows south of the island, leading to very warm water temperatures west of the island.
The warm water provides ideal conditions for non-native fish to prey on out-migrating young salmon in the spring and makes it difficult for adult salmon to swim upstream in the summer. Elevated water temperatures also encourage algal blooms and mosquitoes, degrading water quality.
“The Recommended Plan is Alternative 3a, full removal of causeway without additional riparian habitat restoration,” says the report. https://www.nww.usace.army.mil/Portals/28/YD1135_Main%20Report_Final_2024-10-11.pdf “This plan provides the combined improved habitat net benefit of 53.6 Average Annual Habitat Units for the 50-year annualized cost of $455,000. Removal of the causeway would improve the flows around the island and allow for cooler water to improve habitat for salmonids.
“The total project first cost for the Recommended Plan (not including the feasibility study) is estimated to be $12.4 million.”
The report says: “The purpose and need for the project are to improve ecosystem structure, function, and processes of the Yakima River Delta (Delta) near Richland, Washington, which was degraded by construction of the McNary Dam and Reservoir Project and the Tri-Cities Levees on the Columbia River, including an approximately 550-foot-long and 40-foot-wide earthen causeway connecting the southside of Bateman Island to the mainland. The intended goal of any preferred action, or the Recommended Plan, is to restore riparian and aquatic habitat and ecosystem functions for the benefit of ESA-listed salmonids and other fish, birds, and wildlife in the study area at the Yakima River Delta and, where possible, provide education and recreation access.”
The feasibility report is one piece of a broader environmental review process under the Water Resources Development Act, which mandates the Corps to address degraded ecological conditions in areas under their control. At the request of local partners, the Walla Walla District studied various solutions to improve the ecological health of the Yakima River Delta for fish, wildlife, and people.
The public process began October 2019 with the draft report released for public comment in January 2023.
“USACE is excited to finalize this feasibility report and we look forward to the next phase of the project: design and construction,” said Kat Herzog, Walla Walla District Planner and Project Manager. “This project is very important for improving habitat for salmon, as well as advancing the partnership between the USACE, the State of Washington, and the Yakama Nation.”
“The Yakama Nation is extremely supportive of the Yakima River Delta enhancement project,” said Jeremy Takala of the Yakama Nation Tribal Council. “Over the years of its existence, the causeway at the river delta has caused numerous harms to tribal people through losses to the tribe’s reserved treaty natural and cultural resources. Accordingly, causeway removal is a crucial action for meaningful and effective restoration of salmon and steelhead runs of the Yakima and Columbia river basins and restoration of our tribal practices of Treaty Reserved Rights. The removal of the causeway by the U.S. Army Corps of Engineers would further its performance of its trust obligation to the Yakama Nation to protect Treaty Resources.”
“WDFW is excited to have reached this point in the process of removing the causeway that has negatively affected fish survival and water quality for decades,” said Mike Livingston, WDFW South Central Region Director. “Since release of the U.S. Army Corps of Engineers’ draft of the feasibility study report last year, we have worked with USACE and our partners to answer questions from the public and agencies. I look forward to beginning the next phase of this project to improve the environment for the fish, wildlife, and people who depend on a healthy Yakima River delta.”
The report says the proposed action “is needed because the construction and ongoing O&M of McNary Lock and Dam and the Tri-Cities Levees on the Columbia River have contributed to the degradation of the ecosystem within the Yakima River Delta including poor habitat conditions for native fish and reduced biodiversity. Impoundment of the McNary Dam reservoir (Lake Wallula) inundated the lower 2 miles of the Yakima River, eliminating riparian and aquatic habitat, and changing the hydraulic conditions within the Delta, impacting juvenile and adult salmonid migration through the Yakima River’s confluence with the Columbia River. This inundation turned the southern side of the Delta into a backwater that became ideal habitat for non-native predatory fish and invasive plants. This backwater effect has reduced the ability of the Yakima River to carve and maintain shallow side channels and has promoted excess sediment deposition.
“These changes to the ecosystem have caused delays to upstream migration and contribute to increased straying (diverting from normal migration pathway), diminished health, and lower reproductive success in adult salmonids and the possible increase in predation on smolts.
“Sedimentation from inundation, in combination with blocked flows south of Bateman Island, created a large stagnant, shallow backwater environment with higher water temperatures that supports large monotypic stands of stargrass and algal mats which cause extreme daily fluctuations of dissolved oxygen (hyperoxic to anoxic). Dissolved oxygen levels are crucial for the respiration of aquatic organisms. Coldwater fish species, such as salmonids (salmon, steelhead, and trout), are especially sensitive to fluctuations in dissolved oxygen because their threshold for oxygen concentration is greater and narrower than other warm water fish species. In addition to the direct impacts on juvenile salmon and steelhead health, the backwater conditions support multiple species of predatory fish, which prey on juvenile salmon during their outmigration.”
More information, including the feasibility report, is available on the Walla Walla District website. https://www.nww.usace.army.mil/missions/projects/yakima-river-delta-ecological-restoration/
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