Updated Oct. 21, 2016
The U.S. Army Corps of Engineers continues performing maintenance on the Corps-managed portion of the Mill Creek Levee System. The one-mile-long levee sections segments are critical elements of the levee system which reduces flood risk along 8 miles of the flash-flood-prone creek. The system starts at the Mill Creek Dam, runs through the City of Walla Walla and ends near the Gose Street Bridge, just north of College Place, Washington. Walla Walla County’s Mill Creek Flood Control Zone District manages approximately 7 miles of the system downstream of the Mill Creek Office.
Over many years, the Corps had been trying to formulate a viable solution to address levee-maintenance issues at Mill Creek in a way that would have minimal impact on the aesthetic quality of the popular trails. Because of funding priorities and lack of staffing, we were unable to make much progress in this area. During the time that passed, the vegetation grew out of control and encroached into the levee maintenance zone.
In 2005, Hurricane Katrina changed everything. That flooding disaster shed new light on the importance of levee safety, making it a national priority. A national reprioritization of operations budgets followed to ensure our levees are properly maintained to perform as designed and reduce flood-risk to the lives and property they were built to help protect.
In the Corps’ view of things, not knowing if our levees are in good condition and ready to perform during a flood is an unacceptable risk to public safety. It is not an option to continue to allow non-compliant vegetation to potentially put lives at risk.
Work is planned to be conducted in two phases.
Phase-1 work began on Oct. 8, 2015, and was completed on Dec. 31, 2015. Problematic vegetation was removed from the surface of the levee slopes and 15-feet landward from the levee’s design toe. Non-compliant vegetation on levees blocks visibility during inspections, inhibits access for maintenance, hinders flood-fighting operations, and adds uncertainty to structural performance and reliability, which increases risk to the public. The inability to inspect, maintain and flood-fight typically delays emergency response and contributes to an increased risk of levee failure. Life safety is paramount when decisions are made regarding Corps’ operations.
Phase-2 of restoring the federally managed portion of the Mill Creek Levee System includes removing tree roots that intruded into the levee cross section from the landside slope. District Geotechnical Section engineers (levee experts) examined several test pits excavated at various points along the mile-long levee reach and determined removing problematic roots would require “grubbing” roughly two feet into the levee. In some locations, where tree roots have extended deeper into the levee cross section, more extensive excavation and repairs may be required. A contract to perform Phase-2 work was awarded to KEU Inc., of Vancouver, Washington, on Sept. 14, 2016. Because of the large scope of work and a narrow timeframe in which to accomplish it -- between nesting and flood seasons -- task-orders will be issued over multiple years to conduct work in segments.
Winter 2016-2017 Phase-2 repair work on the south levee will include an area from the division works beginning near the Mill Creek Office, progressing toward the Jones Ditch, just downstream of the wooden pedestrian bridge. Surveying is scheduled for mid-October. Repair and maintenance work involving heavy equipment is slated to begin in early December 2016 and is anticipated to take approximately 3 months to complete. For visitor safety, intermittent closures of parts of Kingfisher and Whitetail trails may be required during the contract performance period. The value of task orders to be performed during Winter 2016-2017 is about $670,000. Additional Phase 2 work will continue throughout the next few years outside of high-flow periods.
This maintenance is necessary to meet National Levee Safety Program requirements in accordance with Corps headquarters regulations and policies. After levee repairs are completed, grasses will be planted on the levees to improve the aesthetics and benefit insects and wildlife.
The Corps went to great effort to minimize the amount of woody vegetation that needed 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 originally constructed design toe in many locations.
Corps leadership, technical experts and planners actively engaged the public and special interest groups throughout the planning and environmental-compliance process. The engagement included news releases, discussions with interested groups and individuals, website and social media outreach, providing media interviews, hosting a public meeting and guiding levee tours in conjunction with the formal public comment period. The Corps considered all public comments received during its decision-making process.
Environmental-compliance documents – as well as fact sheets, videos and other information – are available for viewing or downloading in the right-side column of this webpage.
Work-progress updates and photos can also be found on the Mill Creek Project’s Facebook page www.facebook.com/millcreekdam