Several weeks ago, the Carlton County Soil and Water Conservation District (SWCD) sponsored a tour of the Nemadji Watershed to highlight the parts of a watershed and how they work together. Stops included looking at forests, streams, farms and culverts.
I can hear you asking, "What do culverts have to do with a watershed?" And the answer is, "Quite a lot, actually."
Culverts are something that most of us seldom think about or even notice in our surroundings. Most culverts are just there, not doing anything, and at this time of year, many culverts are hidden by tall grasses.
Culverts are barely given a glance by people unless they are plugged by debris or blocked by ice. When that happens, everyone notices that there is a culvert with a problem and it affects everyone trying to pass through that area.
Culverts can be made from plastic pipe or metal or concrete. They can range from just a few inches to over 10 feet in diameter. But all culverts do the same thing — they transport water from one side of a barrier to the other side. The barrier is usually a road or a driveway, and if culverts didn't transport it, the water would definitely move over the barrier and likely take quite a bit of the gravel or dirt with it.
Culverts are a very important in keeping water from streams or wetlands or fields moving on down to its final destination in rivers or lakes or oceans. However, if a culvert is in the wrong place, facing the wrong direction, or of the wrong dimension, that culvert could instead help the water cause a lot of damage.
“From June 2017 to December 2018, over 2,000 culverts in Carlton County were located and assessed. ”
First, according to Melanie Bomier, Carlton SWCD's water resource technician, when a culvert fails to do its job and a stream or river washes out a road, several tons of road material can be washed downstream.
"This material not only adds more sediment into the watershed, but also covers up stream and wetland plants," Bomier said. "Valuable wetlands and wildlife habitat may be lost."
Second, culverts that fail during storms present a safety hazard. Many flood deaths occur because drivers attempt to cross a flooded roadway and may be unaware of the washed out road hidden by the water. In addition, when roads are closed due to flooding, "it can take much longer for emergency personnel to assist with medical and fire emergencies," Bomier said.
Third, if a larger culvert is the correct size needed, it may have a higher price tag initially, but "there will be a savings in the long run," Bomier said. "The cost of replacing a culvert or lost road bed materials can be very expensive."
In addition, we also "must consider consider the financial and time impact to local residents and businesses when a road has to be closed until repairs are completed," she said.
Because of the role culverts play in water quality, especially in the more challenging red clay areas, the SWCD applied for a grant in 2016 to fund a culvert inventory.
"Past inventories, although useful in many ways, were flawed because they were immediately out of date as soon as they were completed," Bomier said. "We wanted an inventory that would stay relevant and we needed the support and buy-in of the road authority," which in this case was the Carlton County Transportation Department.
The Transportation Department was very interested in the project, according to Will Bomier of the Transportation Department (who, coincidentally, is also Melanie's husband). Thus, an SWCD-Carlton County partnership was launched in 2017 to conduct a culvert inventory on all county-maintained roads. The goal was to evaluate the location, condition and biological and water quality impact of every culvert.
An Enbridge Ecofootprint grant was received to fund not only the culvert project, but also engineered designs of four high-priority culvert replacements. The inventory was conducted by Carlton SWCD staff, as well as SWCD interns from the Conservation Corps of Minnesota and by Carlton County Transportation Department staff and summer interns.
From June 2017 to December 2018, over 2,000 culverts in Carlton County were located and assessed.
One result of the culvert inventory was discovery of a series of undersized and perched culverts on Stony Brook, a tributary of the South Fork Nemadji River. Because of these particular culverts, Stony Brook did not have trout living in it like the neighboring Anderson Creek did even though they had similar habitat with cold water and adequate flow.
The Transportation Department replaced the furthest downstream culvert in 2017 and the Enbridge grant funded the design for the remaining upstream undersized and perched culverts.
One specific culvert had a history of repeated maintenance, and during the 2018 flood, the culvert washed out completely. This culvert's history of road washouts, according to Bomier, "led to approximately 200 cubic yards of road gravel (equal to 20 dump truck loads) washing into the stream."
This gravel "enlarged the stream channel so that during low water flows, the stream was too shallow for adequate aquatic organism (including fish) passage," she said.
In 2018, the Carlton Transportation Department removed the gravel from the stream and restored the channel. The culvert is due to be replaced by the Transportation Department this year using FEMA funding, and the remaining upstream perched culverts will also be replaced using regular maintenance funds.
Thus, by next year, over 2 miles of Stony Brook should be reconnected and restored, based on data collected through the inventory, and hopes are high for the natural return of trout within the next five years.
The culvert inventory project has been a huge success and a very valuable and essential tool for everyone in Carlton County, especially the Transportation Department, for three main reasons:
First, the culvert inventory is "always up-to-date and actually reflects the culvert at that (particular) site. Our maintenance crews update the inventory when they replace culverts in the field," stated Will.
Secondly, as Will Bomier noted, "it helps to know where these culverts are and what shape they're in so that we can replace them before they fail and we have to close a road for costly emergency repairs. We can quickly run reports, identify potential problems, and then prioritize to get them addressed."
In addition, he added that tracking information with the inventory provides for "better planning and cost savings."
"We can input information about how many times we've repaired a culvert or other costs associated with the site, which helps us track how much an undersized or poorly-placed culvert is actually costing us and if it makes sense to get that culvert replaced sooner rather than later," he said.
Lastly, the culvert inventory is an essential tool for emergency response.
"During the 2018 flood," Will Bomier explained, "we were able to quickly look at the inventory to determine the existing and the needed sizes for replacement culverts. This saved the department a lot of time and allowed us to get these culverts replaced right the first time. Thus, we didn't have to go back and replace any of the culverts that were emergency replacements after the flood because we got them replaced correctly the first time."
As an example, a culvert on County State-Aid Highway 13 has washed out three of the last five years.
"After the 2018 flood, the 30-inch pipe was replaced with a 72-inch pipe arch culvert with a natural bottom. At the same time, five truck loads of road material and gravel were removed from the stream and the adjacent wetland," Melanie Bomier said. "The cost of replacing the undersized culvert with an appropriately-sized culvert cost $3,800 less than repairing the damage from the flood."
Due to the hard work of the staff of the Carlton SWCD and the Carlton County Transportation Department, the newly created culvert inventory will continue to be an updated and valuable resource to help the county in its goal to responsibly use taxpayer funds to keep our county roads in good shape.
Side benefits will be safer driving during high water events as well as less sediment washed into our rivers and watersheds. By seriously looking at culverts that are hidden in plain view, that's a win for all of us — people and nature included.
Kim Samuelson is Carlton Soil and Water Conservation District's elected supervisor for District 4. For more information about the culvert inventory project or the importance of culverts, contact Melanie Bomier at the SWCD at 218-384-3891. You can also check out Carlton SWCD on Facebook and at carltonswcd.org.