Naches – Cowiche Flood Risk Reduction and Floodplain Restoration

Project Summary

The Naches – Cowiche Flood Risk Reduction and Floodplain Restoration project transforms the confluence of the Naches River and Cowiche Creek by creating active riverine habitat and improving floodplain connectivity, while providing improved fish passage, water use efficiency and improved sustainable and resilient infrastructure, public safety for both flood hazard and transportation, and other public needs such as recreation and open space retention. In the Naches-Cowiche confluence, the lynch pin to achieving the ability to implement measures that meet the above goals at a transformative scale is the retirement and removal of the outdated irrigation canals, bypasses and fish ladders that litter the confluence, and installing new delivery pipes outside of this valuable confluence.

This Project will catalyze transformative actions by first constructing a new pipeline from the recently completed fish, boat, and sediment friendly Nelson Diversion on the Naches River to the City of Yakima where it will connect to 3 existing surface water irrigation delivery systems. The Nelson Diversion completed in 2023 has been designed and sited to avoid impact to existing and future habitats and allow the retirement of two fish passage limiting irrigation diversions in the Naches-Cowiche confluence. This initial action will allow for implementation of the remaining restoration-oriented project measures in this proposal to directly transform the Cowiche Confluence habitat and access to miles of upstream habitat.

Benefits

1. Improved instream habitat conditions - this project directly improves habitat conditions by removal of the existing diversion systems, reconfiguring lower Cowiche Creek to a more natural vertical and horizontal alignment, restoring and maintaining riparian zones and other native plant communities. These attributes can be directly measured by as-built conditions.
2. Persistence and improvement of the above conditions over time - The FCZD will continue to contract with the North Yakima Conservation District to monitor and maintain the vegetative communities established by this project. The FCZD will conduct inspections of Cowiche Creek after flood events or other events such as fire or invasive species occupation of the site to determine if corrective action is needed. When the majority of this site was acquired, it was subject to conservation easements which the FCZD is required to maintain over time.
3. Restoration and movement of sediment Transport into and through the Reach – FCZD is cooperating with American Rivers and Central Washington University to monitor sediment transport and hydraulic parameters through the project area for the next 5 years. FCZD is responsible for periodically update the Flood Insurance Rate Maps if hydraulic conditions show significant change which is expected at this location. FCZD will monitor channel conditions with LIDAR or Structure from Motion surveys in conformance with FEMA’s data standards to meet these requirements from the National Flood Insurance Program.
4. Compliance with Riparian Restoration Programs - FZCD will seek to ensure that these properties are in compliance with the recently enacted programs for protection of riparian zones for water quality improvement and carbon sequestration throughout the project area.
5. Conversion of large portions of the project area to an open space public park - Current easements on the property also require that it be either in agricultural production or in open space status and available for access to the general public. FCZD will continue to cooperate with the City of Yakima Parks and Recreation Department and the Yakima Greenway Foundation to allow and improve public access to this project location.
6. Improve Streamflow and Fish Passage – after project completion, FCZD will work with Trout Unlimited and the other water rights holders to dedicate the current water rights to instream flow in lower Cowiche Creek, and to remove the existing Ingham/Garretson Diversion on Cowiche Creek. The existing stream gage on Cowiche Creek is expected to continue to document the streamflow improvement. The Yakama Nation monitors the Coho spawning population in the creek, with associated pit tagging and juvenile survival monitoring to determine if fish survival, especially egg to fry survival in the new creek channel, improves over time.