Four culvert replacements improving stream stability, fish passage, and sediment transport

I-89 Culvert Replacements

In addition to supporting the roadways above them, culverts are crucial to the surrounding aquatic ecosystem, providing usable passageways for animals and ensuring steady water flow. In South Burlington, four culverts under Interstate 89 had been deteriorating since their last maintenance in 1984, earning them a poor overall condition rating in recent inspection reports. With the goal of restoring a high-quality aquatic channel under this roadway, Stantec teamed with the Vermont Agency of Transportation to replace the existing culverts completely.

We first evaluated the stream’s geomorphic characteristics to determine our approach for the replacement structures. In addition to applying standard engineering methods in our designs, we also developed and used the US Army Corps of Engineers Hydrologic Engineering Center’s River Analysis System (HECRAS) models at each culvert site. To keep construction costs low, we used an open cut excavation technique which kept the existing culverts in place, forgoing the temporary need for a diversion pipe.

Now in place under the roadway, the new culverts offer substantial improvements in scour resiliency as well as animal and sediment transport.