District progressing on removing Mill Creek levee vegetation

Story by Gina Baltrusch The paved trail on the north side of the federally managed section of the Mill Creek Levee System and pedestrian access to Rooks Park reopened to visitors Nov. 20, following the completion of levee maintenance to […]

Story by Gina Baltrusch

The paved trail on the north side of the federally managed section of the Mill Creek Levee System and pedestrian access to Rooks Park reopened to visitors Nov. 20, following the completion of levee maintenance to remove overgrown vegetation which encroached into the levee’s maintenance-access zone. This levee maintenance, conducted in phases during the past three years, was necessary to meet National Levee Safety Program requirements in accordance with Corps headquarters regulations and policies.

Contractors remove roots and stumps that were intruding into the Mill Creek levee. The U.S. Army Corps of Engineers manages the first mile of the Mill Creek Levee System, Mill Creek Dam and Bennington Lake, located east of Walla Walla, Washington, city limits.

Contractors remove roots and stumps that were intruding into the Mill Creek levee. The U.S. Army Corps of Engineers manages the first mile of the Mill Creek Levee System, Mill Creek Dam and Bennington Lake, located east of Walla Walla, Washington, city limits.

Phase-1 work occurred during October-December 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 for inspections, access for maintenance, hinders flood fighting, and adds uncertainty to structural performance and reliability, which increases risk to the public.

The inability to inspect, maintain or flood fight could delay emergency response or contribute to risk of levee failure. Life safety is paramount for the Corps’ operations.
Phase-2 of restoring the federally managed portion of the Mill Creek Levee System included removing tree roots that intruded into the levee cross section from the landside slope and replacing levee material in accordance with geo-technical and design criteria. District Geotechnical Section engineers (levee experts) examined several test pits excavated at various points along the mile-long levee 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 were required.

Because of the large scope of work and the narrow timeframe to accomplish it — between bird-nesting and flood seasons – phase-2 work was conduct during the late-autumn seasons of 2016 and 2017. Native grasses will be planted on the levees in the spring to improve the aesthetics and benefit insects and wildlife.

Work-progress photographs, environmental-compliance documents, videos, news releases and other information about this levee-maintenance project are available on the Corps’ website at www.nww.usace.army.mil/Missions/Projects/MillCreekLeveeMaintenance.aspx.

About wallawalla