Pearl Builds an Open Top Culvert
At the Missisquoi River Basin Association, we are constantly looking for ways to meet the needs of our community and stay on top of the new and best practices coming out of the Vermont Department of Environmental Conservation.
Over the summer, MRBA Project Manager Ellen Fox attended a training about open top culverts and their implementation. During this training, Ellen got hands on practice installing them. After bringing what she learned back to the rest of the MRBA team, a workday was set up so that everyone else got that same hands on practice.
An open top culvert is a shallow, surface level trough. They are frequently made of wood, metal, or concrete and set flush with a road or trail. Open top culverts are installed across unpaved roads, camp roads, or driveways to manage stormwater runoff and protect the road surface from damage.
According to the Vermont Department of Environmental Conservation Watershed Management Division, “Open-top culverts can be constructed of pressure treated lumber or cedar timbers. Using pressure treated lumber will considerably extend the life of the structure. Spacers placed in the open-top culverts will hold the shape of the culvert and strengthen the structure.
Open-top culverts will vary in length, depending on the width of your road. When sizing an open-top culvert, remember that it should be installed at an approximately 30° angle down slope. Take this added length into consideration when purchasing materials.
Install the culvert flush with the surface of the road. If placed too high, storm water will not enter the structure; if placed too low, it may quickly fill with road material and sediment loosened during installation. The outlet of the open-top culvert should extend beyond the edge of the road. Remove any plowing berms or other debris that could interfere with water flowing from the outlet. Diverted water should flow into a stable area away from the road or open water to allow for infiltration. A stone lined outlet or vegetated area is an acceptable way of reducing erosion at the culvert outlet.”
On a sunny fall morning, the MRBA staff (Pearl in tow) arrived at the project site in Troy to build and install two open top culverts. Luckily for the team, a machine had been on site earlier to dig out the trenches.
The first step was to measure the locations where each culvert would be placed. Once those measurements were taken, the team got to work building the culverts, one box at a time. As always, Pearl proved to be a great project supervisor and was enjoying the sunshine.
After the wood was cut to the appropriate size and screwed together, a layer of epoxy was added at the seams to help hold everything together. The spacers were installed next. The team let the epoxy dry in the sun while they repeated the process with the next box. Pearl was busy standing guard (at a safe distance) while the power tools were in use.
Now that both boxes were built, they were carried down to the implementation locations one at a time. Those open top culverts are heavy! Time and care was spent leveling the box to the driveway to ensure it was flush. The team filled any space between the bottom of the trench and the bottom of the box with sediment.
The next step and perhaps the most labor intensive was to fill in the trench. The dirt that the machine had removed earlier that morning to create the trench was used to fill it back in. It is important to have one to two people going behind the fillers and stamping the sediment down to create a packed down surface. This was Pearl’s favorite part of the day as her friends were using shovels to dig and move dirt around. Medium and large rocks were taken out of the sediment and placed on either end of the culvert, acting as splash pads.
Once the first open top culvert was successfully installed, the team moved on to installing the second one, repeating the process above. It was a satisfying feeling to complete both and have put in a hard day's work, all while learning something new.
Open top culverts need to be cleaned regularly to remove sediments, gravel, leaves, and twigs. It is recommended to check after storm events for accumulated sediment.
Winter snowplowing could easily destroy this type of culvert and result in even greater erosion problems in the spring. However, some people have had success with open-top culverts if the road is not plowed until the ground is frozen and have an attentive plow driver. If you choose to plow a road with an open top culvert, you may want to consider flagging both ends of the culvert to alert the snow plow drivers.
Thank you to Ellen for sharing your knowledge with the team and giving Pearl the chance to be around shovels again!
Contact info@mrbavt.com if you would like to learn more about open top culverts.
