Tag Archives: culverts

Using Mussel Spat Rope to Facilitate Small Fish Passage in Culverts

Low-cost, low-maintenance mussel spat rope can help small fish species navigate through culverts by reducing current velocity and providing protected areas for fish to shelter and rest.  Recent research in New Zealand demonstrated the effectiveness of mussel spat rope—rope with long, dense fibers used in mussel aquaculture— to assist small species fish passing through steep, perched or high-velocity culverts. The successful results from this research led MnDOT to investigate mussel spat rope as a  method to facilitate fish passage in Minnesota’s culverts.

“Minnesota is a headwater state, and we have a responsibility to keep our fish population healthy. Mussel spat rope will be one more effective tool in the toolbox of methods we have to assist fish passage through culverts,” said Petra DeWall, Bridge Waterway Engineer, MnDOT Bridge Office

 What Was Our Goal?

The objective of this project was to determine whether mussel spat rope was an appropriate and effective tool in helping small fish species pass through Minnesota culverts.

What Did We Do?

Investigators conducted a literature review to evaluate previous studies. Then researchers from St. Anthony Falls Laboratory conducted experiments in the laboratory and in the field to investigate the use of mussel spat rope as a fish passage aid.

Hydrodynamic performance. Hydrodynamic performance tests were performed in a 20-inch-wide by 30-foot-long flume fed by water diverted from the Mississippi River into the laboratory. Researchers measured velocity, depth and water surface slope, and sediment accumulation around arrays of ropes. They installed single- and multi-rope configurations and examined many variations of flume flow and depth, recording the rope’s effects on water velocity and turbulence.

In a second experiment, researchers released fine sand into the flume containing two- and four-rope configurations to investigate the rope’s effect on sediment transport. Because the ropes slowed local water velocity, deposits were observed on, between and under the ropes in two different depth tests after one and two hours of sediment feed.

Rope durability, performance and use by fish. Researchers installed mussel spat rope in two Minnesota box culverts: one in the northeast serving a fast current trout stream and one in the southwest serving a slow current prairie stream in critical fish habitat. Double strands of mussel spat rope were installed near a wall in each culvert and examined many times for approximately two years. Each observation included photographic and video recordings of the installations.

2018-13-p1-image
A long interior view to the open end of a large box culvert shows a double strand of mussel spat rope installed in the water along the left wall.

Small fish species’ interaction with the rope. Laboratory investigations of fish behavior with the rope were conducted in a 5-foot-wide by 32-foot-long flume with a raised section representing a box culvert. Two Plexiglas windows allowed viewing. Researchers installed two sets of double-strand ropes along a wall, similar to those in the field sites. Four video cameras tracked motion, recorded overhead views of the flume and captured fish behaviors at the midpoint and ends. Researchers used three species of small fish common to Minnesota: fathead minnow, white sucker and johnny darter. Five fish were released into the test area at a time and allowed to swim for an hour. Their progress and behavior were filmed and analyzed.

What Did We Learn?

Key observations from these investigations follow:

  • Mussel spat rope created small corridors (about 6 inches) of reduced velocity and turbulence along its length, which was sufficient to aid the passage of small fish. Sediment collected in, between and beneath the ropes. The presence of culvert floor sedimentation may assist fish passage.
  • The rope displayed wear over two years in the field, raising a concern about plastic microparticle release into streams. Sediment covered some ropes over time, suggesting a need for maintenance in some culverts. Only a few fish were observed at the field installations.
  • In the laboratory flume, test fish swam near and between doubled rope lengths, apparently taking advantage of the reduced current near and beneath the ropes. While there was variation among species, most fish that swam upstream through the simulated box culvert ended their passage on the rope side, evidence that the rope provided cover and refuge from the current.

What’s Next?

Mussel spat rope will be a low-cost, low-maintenance tool to help small fish pass through culverts. The final report for this study includes guidance for installing the rope. The low-cost method will also be included in an upcoming guide for designing culverts that allow aquatic organism passage.

This post pertains to Report 2018-13, “Use of Mussel Spat Rope for
Fish Passage in Culverts,” published March 2018.

Guidebook Reviews Enhanced Inspection Technologies for Culvert Repair

Enhanced Culvert Inspections - Best Practices Guidebook
The Enhanced Culvert Inspections – Best Practices Guidebook details various culvert inspection methods, including sophisticated technologies such as laser ring scanners and sonar scanners.

MnDOT has developed a guide that compares traditional and enhanced culvert inspection methods and tools, their limitations and costs. The guide also includes best practices for identifying when conventional inspection methods work best  and when enhanced technologies may offer good value.

“We wanted to document how far you can see into the pipe to get a good inspection and when more than an end-of-pipe inspection was needed. We found that there are some cost-effective options for doing more than end-of-pipe inspections,” said Andrea Hendrickson, State Hydraulic Engineer, MnDOT Office of Bridges and Structures.

“Inspection crews need to understand what type of data they want to gather for each situation, and then balance the quality of data required with the cost of the inspection method,” Doug Youngblood, Environmental Engineer, CDM Smith.

What Was the Need?

MnDOT manages more than 100,000 culverts in the state’s highway culvert system. Culverts are inspected routinely to monitor corrosion and other damage that could lead to expensive repairs and highway closures.

New culverts are inspected to confirm that construction measures up to specification. Centerline culverts, which run from one side of the road to the other under pavement, must be inspected every two to six years. MnDOT also inspects culverts in emergencies or when the public notifies the agency of potential damage or blockage.

Inspection typically begins with an end-of-pipe visual investigation, usually aided by flashlight or occasionally by a camera placed in the pipe. If pipes are large enough, inspectors enter the pipe to examine the walls and measure corrosion or other damage, take photos and conduct hands-on examinations.

But not all culverts are large enough for human access, and inspecting damaged or failing culverts can be dangerous. New, enhanced technologies may offer valuable, safer inspection options.

What Was Our Goal?

This project aimed to review common inspection technologies available for culvert and pipe inspection. The results of this review would then be used to develop guidance for choosing a cost-effective inspection strategy that was appropriate for the site and would provide the required data.

What Did We Do?

The research team began by reviewing literature related to culvert inspection best practices. The team then interviewed inspectors from various Minnesota counties and MnDOT districts, and from five other state transportation agencies to gather additional information on best practices.

Laser ring profiler
Laser ring profilers offer precise readings of how much culverts have reshaped under environmental conditions.

Next, investigators reviewed 12 videos of MnDOT inspections performed from 2011 through 2016 and then contracted with a robotics inspection firm to conduct end-of-pipe, laser ring and video inspections of 10 MnDOT culverts that represented a range of sizes, pipe materials and on-site conditions. The results from the three inspection methods were compared to identify best practices, which were incorporated along with the best practices from the literature review and interviews in the Enhanced Culvert Inspections— Best Practices Guidebook.

What Did We Learn?

The guide describes traditional and enhanced inspection technologies and methods, their limitations, costs and best uses for specific situations. Each method offers distinct advantages and disadvantages. End-of-pipe inspection costs about 7 cents per foot, and enhanced inspections cost from 23 cents to $6.50 per foot. Before using enhanced methods, inspectors should have a firm grasp on the quality of data and detail required to best optimize their choices and budget limitations.

End-of-pipe inspections are the fastest and least costly of the methods, but provide the least data. Typically, an inspector with a flashlight can investigate from 5 to 30 feet inside the culvert from the end of the pipe. These inspections work well for determining work conditions and data needs.

Measurement-based inspections include traditional and enhanced methods, including person-entry inspections, hammer sound testing and coring, mandrels and multiple- sensor units such as laser and sonar profilometers. Laser ring scanning offers precise measurement and excellent quantitative data on culvert alignment and geometry. Multiple-sensor units are the most expensive inspection method based on cost per foot and time to process the data, which often takes weeks.

Video inspection typically entails the use of closed-circuit television (CCTV) cameras or consumer-level video from a Hydraulic Inspection Vehicle Explorer (HIVE). MnDOT owns several of both units, which incur labor costs of about 23 cents per foot. CCTV is a national standard for inspection. It offers permanent records with familiar technology; however, lighting, image centering, lens clarity, cumbersome data volumes, and opera-tor training and experience present challenges.

The HIVE is a remotely operated crawler equipped with off-the-shelf cameras and accessories. Developed by MnDOT District 6, the HIVE takes lights and a video camera that is capable of panning and tilting inside a culvert and transmits data wirelessly to a tablet computer. While CCTV offers better measurement ability, a HIVE is lighter, easier to transport and easier to operate. Given that contractor-run CCTV typically costs $2 per foot, the cost of using 750 feet of CCTV would pay for a HIVE.

What’s Next?

In addition to the guidebook, researchers have developed a webinar on culvert inspection options for Minnesota inspectors and crews.

MnDOT will monitor developments among local contractors, as no Minnesota firms currently offer multiple-sensor inspection capability. MnDOT owns a sonar scanner for use on tripods and floatable platforms, and also owns a laser ring inspection unit. Pilot testing and training may make these options cost-effective. Researchers recommend further development of the MnDOT-developed HIVE, including a foam floating platform and a snap-on laser ring scanner for the camera.


This post pertains to Report 2017-16, “Enhanced Culvert Inspections — Best Practices Guidebook,” published in June 2017. 

Designing fish-friendly culverts

Roadways for humans can sometimes create roadblocks for fish, but researchers hope to establish a set of culvert design practices to help aquatic creatures get where they’re going.

Many fish depend on mobility along a river for feeding and spawning. Where roads meet rivers, however, culverts can block fish and other aquatic organisms that can’t navigate changes in current, lighting and other factors.

Waterway barriers threaten an already endangered species of minnow known as the Topeka shiner (pictured above). It can also be a big problem for economically important fish such as trout or northern pike. That’s why the Minnesota Department of Natural Resources prefers building bridges to culverts.

However, bridges are not always economically feasible, and so MnDOT is working closely with the DNR to develop culverts that protect both public safety and the environment.

Photo of boxed culvert
Culverts allow water to pass under roads. Occasionally, they can harm a stream’s fish habitat by inadvertently acting as a barrier to fish passage or migration. There are nearly 11,000 culverts in Minnesota.
Sediment Content 

Recent research suggests that installing boxed culverts differently could greatly improve fish passage.

Culverts are typically placed a little below the streambed with the expectation that the stream flow will naturally fill them with sediment. Researchers tested that assumption and found it to not always be accurate.

“We found that pre-filling the culvert with sediment that replicates the streambed as part of the installation process helped prevent upstream erosion and the development of vertical drops that can become barriers to aquatic movement,” said Jessica Kozarek, a University of Minnesota research associate. “In addition, pre-filling the culvert helped ensure the sediment remained inside the culvert flows were high and water moved quickly during rainstorms.”

MnDOT has been working with the DNR to identify the conditions that determine whether a newly installed culvert will naturally fill with sediment, replicating surrounding streambed conditions, or whether a stream’s water flow will transport sediment out of a culvert.

Using an experimental flume at the University of Minnesota’s St. Anthony Falls Laboratory, researchers tested MnDOT’s standard box culvert design under a variety of stream conditions.

Laboratory simulations suggest that filling a culvert with sediment at installation, rather than allowing it to fill over time is, with some exceptions, generally the best ap­proach for low- and moderate-grade streams. Additionally, steep, fast-moving waters require a filled culvert with structures such as larger rocks to keep sediment in place. These structures also create steps, pools and riffles that enable fish to rest as they move upstream.

MnDOT will use this latest research, along with conclusions from other recent studies, to create a guide for fish-friendly culvert designs.

“Of all the things we’ve studied, there are maybe three or four research projects. This manual will pull it all together,” said Petra DeWall, state waterway engineer at the Minnesota Department of Transportation.

Further research is underway to determine whether aquatic organisms are deterred by low light conditions in long, dark culverts. Researchers are also looking into whether mussel spat rope could be used to create a rough bottom to reduce water speed in culverts with no sediment.

Related Resources

Winter seminars highlight research on work-zone safety, culvert design, and more

Join us in person on the U of M campus or tune in online to the CTS winter research seminars. The seminars will highlight a sampling of the latest transportation research at the U of M.

Here’s this year’s seminar schedule:

Each seminar will be held in Room 50B at the Humphrey School of Public Affairs. Or, if you can’t make it in person, you can watch the seminars live online or view recordings posted after the events. For details about the live broadcasts, see the individual seminar web pages.

There’s no cost to attend, and each seminar qualifies for one Professional Development Hour.

Hope to see you there!

Culvert research aims to protect endangered small fish

The Topeka shiner
The Topeka shiner, a small minnow that inhabits slow-moving prairie streams, was once widespread and abundant in portions of Iowa, Kansas, Minnesota, Missouri, Nebraska and South Dakota. It now inhabits less than 10 percent of its original geographic range.
(Photo courtesy of the Minnesota Department of Natural Resources)

In a new study funded by the Minnesota Department of Transportation, engineers are trying to ensure that new culverts do not degrade the habitat of an endangered fish in southern Minnesota.

The state has already researched how to better accommodate fish passage at river and stream crossings. Now it is looking at design guidelines for culverts that specifically impact the Topeka shiner, a small endangered fish found in five Midwestern states.

In Minnesota, the Topeka shiner is known to live in at least 57 streams, totaling 605 miles, within the Big Sioux and Rock River watersheds.

“The Topeka shiner is reported to have been erased from about 50 percent of its historic range in Iowa and much of its range in Minnesota, which is why Minnesota is so intent on doing what it can to help this fish thrive here,” said Alan Rindels, MnDOT’s project coordinator for the research.

The Topeka shiner is endangered due to the degradation of stream habitat, stream channelization, non-native predatory fishes and construction within waterways.

Culverts might impede the passage of this small minnow for a number of reasons, including that they might be too long, lack sufficient depth or carry water too fast.

Culverts allow water to pass under roads.
Culverts (also called small bridges) allow water to pass under roads. Occasionally, they can harm a stream’s fish habitat by inadvertently acting as a barrier to fish passage or migration. On the West Coast, large-scale efforts are under way to protect migratory salmon, and in Minnesota, culvert designers are concerned about fresh water species.

In addition, long culverts block sunlight, which possibly discourages fish from swimming through. Typically, older culverts are replaced with longer culverts to improve road safety and minimize maintenance costs. To eliminate or minimize impacts to the Topeka shiner, the state is trying to determine if light mitigation strategies are necessary.

Researchers from the University of Minnesota’s St. Anthony Falls Research Laboratory will monitor a newly installed culvert (110 feet in length) and a few other culverts in critical Topeka shiner habitat streams during spawning and fall movement.

Additionally, a laboratory-based light manipulation experiment will examine the behavior of the warm-water fish when presented with a dark culvert.

Guidelines for culvert design in Topeka shiner habitat will be developed based on these results, as well as examples from neighboring states. The state is also collaborating with the U.S. Fish and Wildlife Service and affected Minnesota counties.