Maintenance Operations for the Drainage Districts:
The primary mission of the Columbia Corridor Drainage Districts is to manage the Columbia River Floodplain to prevent flooding of landowners from high water levels in the Columbia River and from storwater runoff. The Drainage Districts manage both external flooding, with levees along the Columbia River and from storm water runoff. The drainage Districts manage both external flooding, with a closely monitored system of pump stations and conveyance systems.
The Columbia Corridor Drainage Districts include: Peninsula Drainage District No. 1, Peninsula Drainage District No. 2, Multnomah County Drainage District No. 1 and Sandy Drainage Improvement Company.
Internal Flood Control:
For the Drainage Districts to manage a reliable flood control system, storm water must flow through a series of culverts, ditches and the Upper Columbia Slough to reach pump stations to be discharged outside the districts. Each part of the storm water conveyance system has to be engineered and maintained in order to assure the system has the capacity to convey a 100 year storm event.
Maintenance includes removing garbage, tires, appliances, beaver dams and trees that have been thrown or haven fallen into the water. Mowing the conveyance banks with tractors and controlling invasive weeds is required annually to allow the district to inspect the system during high flows. Aquatic plant growth and silt from farmlands, parking lot and street runoff accumulate in the ditches and sloughs and must be removed periodically. The Drainage District equipment and techniques are designed to dredge the conveyance systems to maintain the hydraulic capacity while preserving upland habitat.
The district inspects the conveyance system once a week and the pump station bi-weekly. Normal weekly inspections and maintenance to the pump stations includes checking pump lubrications, electrical connections, security systems and clearing debris from intake grates. Annual maintenance includes performing a vibrations analysis to the pump and motors, change lubrications fluids, inspecting the pump wet wells servicing the electrical systems and buildings.
External Flood Control:
The districts have levees on the North, keeping the Columbia River at bay, and on the South along the lower Columbia Slough protecting properties from the Willamette River.
The districts levees are a part of the Army Corps of Engineers Federal Levee Program and must be maintained to Federal levee standards. The levees are inspected by the Army Corps of Engineers annually for compliance to the standards. The district inspects the levees based on the river and seasonal conditions. The levees are inspected for erosion, loss of rip rap, burrowing animals, debris accumulation, invasive weeds, non permitted development on or adjacent to the levee, access roads and gates. If a deficiency is noted the district repairs the damage immediately. Annually the district mows the levees and controls the invasive weeds to maintain a good grass cover on the levees. As the top soil surface area on the levee start to erode the district will remove the grass cover of the levee and resurface the levee with 12 to 18 inches of new top soil and then hydro-seed the new surface.