Otak Completes ODOT Project to Repair and Upgrade Bad Banks Culvert
Lying beneath fifty-feet of fill and one of Oregon’s major recreational highways, was an ailing 75-year old concrete culvert with a history of operation and maintenance problems. The culvert in question funnels the Bad Banks Creek underneath Oregon State Route 22 about four miles east of Gates, Oregon. Working with the Oregon Department of Transportation, Otak’s hydraulics engineering team led a design and construction project to repair damage to the 300 foot-long culvert, improve stream flow and provide safer access for ODOT inspection and maintenance crews and equipment.
The Bad Banks Creek culvert at HWY 22 was subject to abrasion from sediment flowing in the stream channel, which over time, had worn down the concrete culvert and exposed the rebar reinforcement. The culvert also presented various safety issues for ODOT inspection and maintenance crews as it was difficult to access either end of the culvert due to steep slopes and lack of space to operate. While extending the life of the culvert was a priority, the other significant part of the project was to improve access for long-term maintenance.
Otak was hired by ODOT in May of 2019 to provide design services for repairs to the culvert to extend its service life and to modify the culvert entrance to improve access for long-term operation and maintenance of the culvert. Otak was then hired to provide construction administration, engineering, and inspection services during construction, which began in June 2020.
Extending the life of the culvert made sense—the typical life-span of concrete reinforced culverts is 75-100 years and it would have been very expensive to replace. As Otak Project Manager and Principal Kevin Timmins, states, “if the culvert ever does get replaced it will likely be with a bridge.” Rather than a costly bridge project with major disruptions to traffic along HWY 22, ODOT was able to get money and permits to make repairs and modifications and chose to work with Otak on a design to prolong the life of the culvert while also addressing the safety and access issues.
To mitigate the effects of streamflow and sediment abrasion, the culvert was lined with six inches of new concrete. The upstream end of the culvert was also extended, a more gradual transition into the culvert was added for better streamflow, and debris fins were installed at the upstream end to catch large debris so it doesn’t enter the culvert. The modifications had the added benefit of allowing the maintenance access road to come further down. As Kevin explains, “previously the access road just stopped at a steep vertical drop off into the culvert. By extending the culvert we were able to bring the road down and across the top of the culvert to the other side where we were able to create a level area where ODOT will be able to park an excavator and reach upstream of the debris fins in the event they need to be able to clear debris in front of the culvert.”
Ten days before substantial completion in September of 2020, the Beechie Creek fire burned through the construction site, scorching the forest vegetation, melting the stream bypass system, and causing damage to a portion of the freshly poured concrete. Otak has been working with the ODOT to manage the response at this site, including project closeout and plans for additional site stabilization and concrete repairs to be constructed in 2021.
“One of the reasons we were excited to work on this project was the fact that we were already familiar with the site,” Kevin stated, “and that our water resource team has a lot of experience in working in streams. They understand the hydraulic conditions, how to manage streamflow during construction, how to accommodate construction access.” This project was an opportunity for Otak’s hydraulics team, who possess deep knowledge and capacity for hydraulic engineering, to work in tandem with Otak’s structural team. Additionally, Otak has experience working on projects in environmentally sensitive areas, and mitigating the environmental impact during construction was a priority and requirement of the state.
In the end, the culvert repairs have staved off a costly bridge replacement by extending the life of the culvert and ODOT inspection and maintenance staff now have better and safer access to the culvert.