While many focus on improving the more than 100 miles of classified trout streams and habitats in Jackson County, a perched culvert is often an overlooked aspect that can ruin a perfectly good habitat with one poor decision.
A perched culvert is when the water flowing through a culvert doesn’t flow through at an even level, often times with the downstream end of the culvert higher than the water level.
“We can do a lot of habitat improvement, but if these culverts are installed wrong, you have just cut off all of that habitat work that you have done upstream,” Jackson County conservationist Gaylord Olson said.
A perched culvert can create issues that can affect several different aquatic species including trout.
“Part of the problem is connectivity for the habitat. When fish are spawning and moving within the aquatic corridor and they need to get past a culvert, if it is above the stream bed, a lot of the smaller fish in particular can’t get upstream to where they need to go for fish spawning,” Maureen Millmann, DNR municipal transportation policy coordinator, said.
A severely perched culvert where water pours out of the downstream part of the culvert can prove especially troublesome.
“It can cut fish off from migrating to various areas that the fish might use during their life stages. Different parts of streams act to support different life stages of fish,” DNR fisheries biologist Dan Hatleli, who works with Jackson, Trempealeau and Buffalo counties, said. “It is a travel barrier that they can’t physically make it upstream from where that culvert sits.”
Hatleli said that having a perched culvert can drastically change the biology of a stream, which can vary anywhere from being less than a mile to more than 30 miles.
“If all of the road crossings were placed correctly, you may have a very vibrant self-replicating trout stream there, whereas if you have even one improperly placed culvert in that particular system it might actually reduce the quality or prevent the establishment of a self-replicating trout population,” Hatleli said.
A perched culvert can also cause the upstream and downstream water to pool, which the sun then warms up.
“Trout and a lot of species that live in trout streams are there because of the conditions in the stream, and one of those that is especially important for trout is cold water,” Hatleli said. “Anytime you expand a water’s surface, you are expanding how much sunlight hits that water.”
In general the temperature of the water needs to be below 70 degrees otherwise the trout can be subjected to thermal stress.
What’s bad for fish is often bad for the road
Having a perched culvert can also lead to several issues with the road itself.
“If it is too high, there could be turbulence where the water could start undermining the base of the road of the culvert itself,” Olson said. “In some cases where culverts are perched, the road bank is steep as well.”
Since perched culverts tend to be too short, the banks of the road also tend to be steeper, making for unsafe driving conditions.
Flood conditions have also encouraged some municipalities to go with larger culverts to increase the volume of water the culvert can handle, which can inadvertently help the fish population. Drought and flood conditions can also change whether a culvert is perched, which provides additional hurdles for discovering a perched culvert.
“We really see all degrees of it all over Wisconsin,” Millmann said. “Some culverts have perched over time because when they were placed maybe they were placed at the stream bed, and then the nature of the stream is that the stream begins to down-cut.”
While some culverts have perched over time, the problem may not be resolved when a new culvert is put in 30 to 50 years after it was originally installed.
“The next thing is when they come back to replace them, if people are not checking to make sure they are done right the first time, they may install it the same way the previous one had been done,” Olson said. “Some of these water bodies could have a long time that those head waters may be cut off from trout spawning.”
Steps when putting in a culvert
Before a municipality puts in a culvert, they should be talking to the DNR to see if they need to get a permit. The permit would stipulate how the municipality would need to put in the culvert.
“If you are doing any kind of work within the waterway, you probably do need permits from the Department of Natural Resources,” Millmann said.
The DNR tries to encourage municipalities to take a look at the stream both upstream and down and figure out where they could place the culvert at an elevation that would allow the stream to act as if the culvert wasn’t even there.
Millmann admits the DNR often finds out about perched culverts through road projects because the municipality feels like the culvert has failed.
“Sometimes it is failing because of that perched aspect that this stream is trying to do something at that road that it is not really able to do because of the perched culvert,” Millmann said.
If a municipality would like to correct a culvert that is placed incorrectly, they can work with Olson who coordinates applications for municipalities to find funding to fix perched culverts.
“I help if there is money available to help defray the costs of installing them properly to make sure that those fish or other aquatic species can go upstream from that area that they can’t now,” Olson said adding that the federal government and Trout Unlimited sometimes provide funding.
Olson also reached out to the Jackson County Highway Department to see if there was anything they could do when a town requests culvert aid from the county.
The Highway Department discussed the options during their December meeting and decided to have a conversation with the towns prior to construction about perched culverts instead of just inspecting the culvert afterwards.
“Maybe it is a point where we need to make contact with them,” Randy Anderson, previous Jackson County highway commissioner, said during the December meeting. “The county would be willing to pay the additional cost for lengthening out that culvert so you can get it down to the stream bed.”
The Highway Department already requires all culverts applying for culvert aid to be at least 48 inches wide.
Millmann also said that the DNR has a Road/Stream Crossing Workshop. If you are interested in attending, please contact the DNR.