Culverts are hidden watershed wonders

Several weeks ago, the Carlton 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 forests, streams, farms, and culverts.

What do culverts have to do with a watershed? Quite a lot, actually.

Culverts are something that most of us seldom think about or even notice in our surroundings. 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.

Made from plastic pipe or metal or concrete, culverts 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 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 dimensions, that culvert could instead help the water cause a lot of damage.

According to SWCD water resource technician Melanie Bomier, 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. Properly sized culverts help us keep road materials where it's supposed to be: on the road!"

Second, culverts that fail during storms present a safety hazard. Many flood deaths result from drivers attempting to cross flooded roadways, unaware of washed-out roads 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.

Third, if a larger culvert is the correct size it may have a higher price tag initially, but there will be a savings in the long run, she added.

"The cost of replacing a culvert or lost roadbed materials can be very expensive," Bomeir said. 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.

Because of the role culverts play in water quality - especially in the more-challenging red clay areas - the SWCD applied for a Enbridge Ecofootprint grant in 2016 to fund a culvert inventory and also engineer designs for four high-priority culvert replacements.

"Past inventories, although useful in many ways, were flawed because they were immediately out-of-date as soon as they were completed," Bomeir said. "We wanted an inventory that would stay relevant and we needed the support and buy-in of the road authority" (the Carlton County Transportation Department).

The transportation department was very interested in the project, according to the department's Will Bomier(who, coincidentally, is also Melanie's husband). Thus, an SWCD-County partnership was launched in 2017 with the goal to evaluate the location, condition, and biological- and water quality impact of every culvert on all county-maintained roads.

June 2017 to December 2018, more than 2,000 culverts in Carlton County were located and assessed. The inventory was conducted by Carlton SWCD staff, SWCD interns from the Conservation Corps of Minnesota, transportation department staff and summer interns.

One result of the culvert inventory was the 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 to allow adequate passage of aquatic organisms, including fish.

In 2018, the 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 with FEMA funding, and the remaining upstream perched culverts will also be replaced using regular maintenance funds. By next year, more than 2 miles of Stony Brook should be reconnected and restored 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 for several reasons.

1. The culvert inventory is always up-to-date because maintenance crews update the inventory when they replace culverts in the field now.

2. It helps to know where these culverts are and what shape they're in so that county workers can replace them before they fail and/or have to close a road for costly emergency repairs.

"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," Will Bomier said.

3. It has also saved the county money and time.

During the 2018 flood, the transportation department was able to quickly look at the inventory to determine the existing culverts and the sizes needed for replacement culverts. That meant they could 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," he said, pointing to a 30-inch pipe on CSAH 13 that was replaced with a 72-inch pipe arch culvert with a natural bottom.

"It was noted that culverts sized to the stream survived the flood with little damage and prevented waters from overtopping the road," Melanie Bomier added. "This saved money in costly repairs and allowed county residents to continue using the roads after the flood."

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 SWCD'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 them out on their website at http://www.carltonswcd.org.