A county-wide culvert inspection and inventory effort has revealed the need for increased emphasis on this critical but often hidden element of the county’s roadway infrastructure.
The Culvert Facts
A culvert is a structure, similar to a bridge, which allows water to flow beneath a road surface. The purpose of a typical culvert is to convey creeks, streams, and storm runoff, but some are installed to help animals, including livestock and wildlife, cross the road. Culverts come in a variety of shapes and sizes ranging from 8-inch plastic pipes to 12-foot concrete boxes.
Washington County’s 1,300-mile roadway system includes about 3,000 culverts, which if laid end to end would stretch about 27 miles (from Wilsonville to Banks). Recent culvert inventory and condition inspections indicate that about one-third are in need of repair or replacement.
Flooding, road failures, property damage, and erosion can occur when a culvert fails to properly convey water. These failures can create dangerous driving conditions, expensive repairs for property owners, costly detours, and damage to the drainage system and to the environment.
Most of the funding for culvert replacements comes from existing road maintenance dollars. Since Washington County’s pavement management program has resulted in reasonably good pavement conditions throughout the major roadway system, some money is being shifted from pavement overlays to fund culvert replacements. A portion of the funding is also coming from House Bill 2041 – state money from increased vehicle license and tag fees. Funds may also come from the county’s Major Streets and Transportation Improvement Program (MSTIP).
One specific culvert replacement project, on Kruger Road at Chicken Creek, was partially funded with federal dollars from the Bureau of Land Management and the U.S. Forest Service. These funds were made available through a grant from the National Fish and Wildlife Foundation in cooperation with the local environmental group, Raindrops to Refuge.
Washington County also received funds from the Oregon Watershed Enhancement Board (OWEB) to help with the replacement of a pair of undersized culverts on Greener Road. These culverts were replaced with a small bridge in 2009. (See photos of Greener project.)
The Culvert Challenge
With limited funding, the challenge is to decide which culverts to replace first. Factors that can influence a replacement include risk of failure, the actual condition of the structure, whether the road is scheduled for pavement work in the near future, detour availability and length, traffic volumes, and cost. And we look for opportunities to replace aging culverts as part of upcoming MSTIP road improvement projects.
From the time a culvert is selected for replacement, a typical project can take up to a year. Formal engineering, permitting (federal, state, and local), and right-of-way activities occupy the majority of the project development phase. Most of the larger culverts are contracted to private construction companies, requiring a formal bidding process that takes several months. Another element is the timing of the actual construction activity. Most culvert crossings have restrictions on when the work can be done. Much of the work can happen only between July 15 and September 30 to avoid fish migration periods in our rivers, streams, creeks, and waterways.
Most of the new culverts are much larger than the structures being replaced. New culverts are sized to accommodate required flow capacities, and fish and wildlife passage. Most of the time, the controlling factor when choosing the size and configuration of a new structure is based more on environmental requirements than on drainage requirements. (See: Why are the new culverts so big?)
Meeting the Challenge
Washington County plans to replace a few major culverts each year through our maintenance program. This does not include replacements that are also occurring as part of MSTIP road improvement projects or as part of Clean Water Services projects.
Washington County recognizes that a short-term inconvenience may exist during the construction of these projects. However, long-term benefits include a new structure that will last approximately 75 years, improved drainage, and improved habitat for fish and wildlife.
Culvert replacement candidates are constantly being considered, although construction dates are not yet known for every project. As projects are scheduled and construction dates become known, they will be posted on the Washington County Roads Web site at www.wc-roads.com.
Culverts on the following roads were replaced in 2010:
- 97th Avenue between McMillan Street and Canyon Road
- Cochran Road near Timber Road
- Old Cornelius Pass Road between Phillips Road and Rock Creek Road
Culverts on the following roads are being considered for future replacement pending funding availability:
- Dairy Creek Road between Meacham Road and Fern Flat Road
- David Hill Road between Thatcher Road and Antler Drive
- Jacktown Road between Hachett Lane and Rosedale Road
- Rosedale Road between 209th Avenue and 229th Avenue
- West Union Road between Jackson Quarry Road and Groveland Road
Washington County’s culvert replacement program is another example of our commitment to operating the county roadway system in a safe, cost-effective, and environmentally responsible manner.