Corps of Engineers finalizes Mill Creek levee maintenance plan
WALLA WALLA, Wash. – Following intensive U.S. Army Corps of Engineers review and consideration of public comments which led to a modification of its preferred alternative, the Corps’ Walla Walla District Commander Lt. Col. Timothy Vail approved a Finding of No Significant Impact (FONSI) today for its plan to perform vegetation maintenance on the Corps-managed section of the federal levee system along Mill Creek in Walla Walla.
To ensure the levees will perform as designed, the Corps will remove about 6 acres of woody vegetation from the landward side of the levees, beginning in October 2015, after bird-nesting season, and a qualified biologist inspects the trees prior to removal. The maintenance is necessary to meet National Levee Safety Program requirements in accordance with U.S. Army Corps of Engineers Headquarters regulations and policies.
Once the vegetation-free zone is cleared and levee repairs completed, grasses will be planted to improve the aesthetics and benefit insects and wildlife. Vegetation outside the zone will be allowed to develop naturally.
Additionally, based primarily on input received during the July 24 through Aug. 24 public comment period for the Environmental Assessment (EA) and draft decision document (FONSI), the preferred alternative was modified to include (during Phase II) a requirement to look for and identify, if possible, opportunities for additional plantings in overbuilt areas or outside the levee’s 15-foot vegetation-free zone, where existing real estate interests will allow. If identified, such additional plantings will be added to the Mill Creek Project planting strategy.
“I thank all who took the time to provide thoughtful, substantive comments on the Environmental Assessment, which led to this change in the Corps’ plan,” said Vail. “Walla Walla can look forward to the Mill Creek Project continuing to provide vegetation for aesthetics, recreational enjoyment and wildlife benefits, while also having a well-maintained levee that reduces flood risk to lives and property.”
Corps levee vegetation standards require removal of woody vegetation from the levee crown, and to a distance of 15 feet from the levee toe on both sides of the levee or to the project right-of-way, whichever is closer. Roots growing into the cross section provide a path for water to flow through the levee, increasing the potential for seepage problems to occur, putting the integrity of the embankment at risk of failure.
The Corps has gone to great effort to minimize the amount of woody vegetation that needs to be removed on the Mill Creek levees. The levees were surveyed, measuring the maintenance zone from the base of the original design slope (called the toe) instead of the actual physical slope, which extends far beyond the design toe in many locations.
Corps leadership, technical experts and planners actively engaged the public and special interest groups throughout the planning and EA/FONSI process, including news releases, discussions with interested groups and individuals, website and social media outreach, providing media interviews, and a public meeting and levee tour on Aug. 12 in conjunction with the formal public comment period. The Corps considered all public comments received during its decision-making process.
Final FONSI and EA documents – as well as fact sheets, videos and other information – are available on the Walla Walla District website at www.nww.usace.army.mil/Missions/Projects/MillCreekLeveeMaintenance.aspx