When wildfire removed the vegetation from a 116 square mile forested watershed in Eastern Oregon, the estimated increase in runoff was over 8 times the pre-fire runoff for a 2-year storm event. The existing 5' diameter culvert under US 395 was not only undersized for the new 50-year design storm, but was predicted to become blocked entirely by sediment and debris. Sudden loss of the highway would cause extensive damage to property and homes downstream as well as sever a critical transportation route. For these reasons, an emergency replacement structure was needed to cross Vance Creek.
"Oregon Department of Transportation (ODOT) received emergency orders to replace this and another culvert prior to the first snow fall," stated Caroline Barnes, P.E., Hydraulics Engineer with ODOT.
The presence of ESA-listed steelhead became critical to the design of a replacement crossing and a new structure with a minimum 20' span was recommended to handle the increased runoff and debris and provide fish passage. Since US 395 was the only major road in the remote area, the traffic volume and lack of potential detour routes (due to the surrounding mountainous terrain) limited road closure time to a maximum of ten days.
After deliberation, a 5 gage, 20' diameter round MULTI-PLATE® with square cut ends was selected as the best solution for its quick installation and the technical and installation support provided by Contech Engineered Solutions. While the road was being excavated, the 144' long MULTI-PLATE was assembled off site in 30' segments, allowing the structure to be installed more quickly and efficiently upon delivery.
"ODOT evaluated several options for replacement structures," added Scott Hayes, P.E., Bridge Engineer with ODOT. "The immediate response of Contech engineers to work toward finding a product that could arrive in time and be placed rapidly was invaluable to meeting the governor’s deadline and reopening this critical highway."
The product was selected and designed in less than three weeks and installed in 10 days resulting in a successful project. The new structure met all performance expectations.