Category Archives: Environment

Environment, Materials and Construction

Culvert Design Manual Provides Guidance for Accommodating Fish Passage

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Several years of research have culminated in the publication of a culvert design manual that promotes the safe passage of fish and other aquatic organisms, as well as stream connectivity, throughout the state.

“Engineers designing culverts for Minnesota’s diverse ecological regions will benefit from this document, which offers sound guidance from many practicing experts about how to design culverts that allow aquatic organism passage and preserve stream integrity,” said Petra DeWall, former Bridge Waterway Engineer, Minnesota Department of Transportation (MnDOT).

What Was the Need?

Minnesota’s 140,000 miles of roads and approximately 92,000 miles of streams and rivers meet at tens of thousands of places. Culverts are a cost-effective solution to allow traffic to cross over smaller waterways. Historically, culverts have been designed with the safe passage of vehicles in mind. Recently, a state and national appeal for the safe passage of fish and other aquatic organisms, as well as for waterway integrity and connectivity, has influenced culvert design.

A pair of Topeka shiner fish
The Topeka shiner, once found throughout the state, is one species of federally endangered fish in Minnesota that must traverse culverts to survive.

MnDOT has supported many research projects examining fish and aquatic organism passage (AOP) through culverts, and nationally, a number of published resources exist on appropriate design. Because of the variety of ecological regions in the state, the range of culvert geometries and many other factors, no single solution can accommodate AOP through culverts statewide. A comprehensive culvert design guide was needed to inform designers about solutions that can effectively facilitate the movement of fish and other aquatic organisms in Minnesota while maintaining healthy streams.

What Was Our Goal?

The objective of this project was to produce a comprehensive and accessible culvert design guide that could be used by Minnesota practitioners to design culverts for AOP and stream connectivity. The guide would provide the following benefits:

• More efficient culvert design and permitting process for AOP.
• A central definition of typical designs, which would improve contractors’ familiarity with designs and lower construction costs.
• Avoidance of designs that could be detrimental to the natural environment.
• Avoidance of designs likely to lead to roadway damage and need for repairs.
• Fishery improvement through increased stream connectivity.

What Did We Do?

To determine the scope of the guide, researchers worked with experts from the Minnesota Department of Natural Resources (DNR), the U.S. Forest Service and others with knowledge of civil engineering, AOP and stream geomorphology.

They then sought information for the guide from a wide range of authoritative resources. A literature search examined current and past research by the research team and others; guidance documents from federal agencies; guidance from other states; permit requirements from the DNR and other agencies; and databases of fish populations, stream attributes and culvert data. The literature search also sought to reveal gaps in knowledge where further research specific to Minnesota was needed.

Additionally, researchers surveyed a cross section of highway design engineers and managers from MnDOT, county and city agencies, resource agencies and engineering consultants to identify current design practices for AOP and stream connectivity, and the degree of their effectiveness.

What Did We Learn?

The project resulted in the Minnesota Guide for Stream Connectivity and Aquatic Organism Passage Through Culverts, a thorough guide for culvert designers, hydraulic engineers and others involved in culvert design and construction in Minnesota. Topics addressed in the guide include:

• The need for culvert designs that include AOP and stream connectivity, as well as the current regulatory context.
• An overview of culvert design, categories of design methods that incorporate AOP and waterway connectivity, and a list of best practices.
• Site characteristics, analysis and tools related to energy dissipation, hydraulic analysis for AOP and sediment transport.
• A design method selection chart, information on certain designs and references for further information.
• Further guidance about design issues such as multiple barrel and floodplain culverts, grade control, retrofits and other cost considerations.

What’s Next?

The culvert design guide will be made available to users online. Future considerations for this project include an associated webinar and efforts to coordinate information presented in the guide with expectations and permitting requirements of MnDOT departments charged with culvert creation and implementation. Additional research is underway to assess culverts and fish passage with respect to storm vulnerability and future hydrologic scenarios.

This post pertains to the MnDOT and LRRB-produced Report 2019-02, “Minnesota Guide for Stream Connectivity and Aquatic Organism Passage Through Culverts,” published January 2019.

Education, Environment, Maintenance Operations, Traffic and Safety

Pilot Program Promotes Benefits of Snow Fences

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A new program piloted in western Minnesota to increase snow fence use among private landowners has been so successful that MnDOT is looking at rolling it out statewide.

The University of Minnesota’s Center for Integrated Natural Resource and Agricultural Management worked with MnDOT District 8 staff for more than a year to develop and test a snow fence outreach program that could be used by MnDOT district offices.

“After our training, we saw a 300 percent increase in the number of standing corn rows, and that was on the initiative of a few people in the maintenance group. We’d like to spread the training to other districts,” said Dean Current, Director, University of Minnesota Center for Integrated Natural Resource and Agricultural Management.

Background

Living snow fences are natural vegetative barriers that trap blowing snow, piling it up before it reaches a road, waterway, farmstead or community. It could include leaving a few rows of corn or hay bales along the road side, or even temporary fencing.

MnDOT has about 3,700 sites that are suitable for snow fences. It estimates that if 40 percent of problematic sites had snow fences, the state could save $1.3 million per year in snow management costs. Despite the cost, safety and environmental benefits, private landowners have shown limited interest in the program. An effective outreach program was needed along with strategies for identifying MnDOT personnel who could promote the practice and recruit landowners to the program.

“If we can implement our blowing snow control program more consistently, we can help reduce crash severities, improve operational efficiencies due to snow and ice control measures, and improve the mobility of the public,” said Dan Gullickson, Snow Control Program Administrative Coordinator, MnDOT Office of Environmental Stewardship.

How Did We Do It?

In January 2016, investigators surveyed MnDOT District 8 employees to gauge their understanding of snow fences as well as their approach to working with landowners to implement blowing snow control measures. The investigators studied survey responses to assess awareness of and interest in promoting the use of snow fences and grading to reshape road environments for snow and erosion control. They also examined snow fence programs from around the country, identifying types of snow fences used and characteristics of programs that successfully recruit landowner participation.

A permanent snow fence along a rural highway.
A permanent snow fence along a rural highway.

Results from these efforts were used to design an outreach program that was presented to District 8 staff. In January 2017, investigators surveyed the staff to evaluate the training and redesign the program accordingly. Finally, investigators evaluated market values of various snow fence designs.

What Was the Impact?

Initial survey results identified two relevant types of district personnel: maintenance and program delivery staff. Maintenance staff involved in plowing and road care interact more with landowners than do program delivery staff, who design or redesign roadways and may be involved in acquiring land for snow fences. Though tailored for each group, all training described the MnDOT blowing snow control program and its implementation, the role of snow fence coordinators, operational benefits and awareness of how promotion of the program fits within the scope of an employee’s duties.

Keys to the success of snow fence programs around the country include strong relationships and direct communication with local landowners, funding, landowner interest in conservation and public safety, and observable benefits.

A follow-up survey showed marked improvement in staff knowledge of the program and willingness to promote it. Landowner participation grew from four sites to 15 in the year after training, due mostly to maintenance staff participation. Survey respondents suggested potential program improvements such as more program champions; outreach in spring and summer at community and farmer gatherings as well as at local and state fairs; and a clearer understanding of how program promotion fits within job responsibilities.

The market study demonstrated that nonliving snow fences, though the most expensive option for MnDOT, offer the largest benefit per acre. Landowners seem to prefer living snow fences and standing corn rows. MnDOT may wish to raise the annual payment for all living snow fences.

What’s Next?

Considerations for MnDOT include implementing the training program in other districts, further defining central and district staff roles in snow fence promotion and implementation, incentivizing snow fence champions, developing more outreach material and maintaining relationships with landowners.

A new project currently under way aims to further expand these efforts.

This post pertains to Report 2017-42, “Expanding the Adoption on Private Lands: Blowing-and-Drifting Snow Control Treatments and the Cost Effectiveness of Permanent versus Non-Permanent Treatment Options.” Related research can be found by searching “snow fences” under “Projects” at MnDOT.gov/research.

 

Environment

New Project: Re-Using Water at Safety Rest Areas and Truck Stations

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Water is being drawn out of the state’s aquifers faster than it is being replenished, so public agencies like MnDOT are increasingly interested in figuring out how to reduce water usage.

A two-year research project underway at MnDOT is investigating how the agency can re-use wastewater at its safety rest areas and truck-washing stations. In addition to preserving groundwater, MnDOT hopes to reduce utility and septic system costs.

MnDOT owns and operates over 1,000 buildings, including 68 safety rest areas, 137 truck stations, 18 regional/headquarters maintenance sites and 15 weigh stations and truck scales.

These facilities either discharge their wastewater to a subsurface sewage treatment system or a wastewater treatment plant.

Truck station with vehicles in parking lot
Maplewood Bridge Truck Station

Researchers from the University Of Minnesota’s Onsite Sewage Treatment Program have been hired to investigate the potential avenues for wastewater re-use at MnDOT. They will consider when re-use makes sense from a regulatory, environmental, economic and management perspective; recommend the most appropriate applications for reuse and identify any challenges with implementation.

Potential benefits include:

  • Preserve ground and drinking water for potable drinking.
  • Reduced life-cycle costs in areas where low-producing wells could meet drinking water needs while reused wastewater could be used for toilet flushing and equipment wash-down.
  • In areas with municipal water, lower water utility costs.
  • Increased longevity of septic systems due to decreased loads.

As the state, counties, or cities construct new facilities or upgrade existing ones, this research will provide insight into what options are readily available to reduce water consumption and improve water efficiency. If these types of reuse systems are demonstrated by MnDOT, then they could lead to usage by other properties across Minnesota.

Watch for new developments on this project.  Other Minnesota research can be found at MnDOT.gov/research.

Environment, Materials and Construction

Pervious Concrete Pavement Reduces Runoff into Shoreview Lake

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The city of Shoreview, Minnesota was on the right track when it took the unusual step of paving a residential neighborhood with pervious concrete to help control stormwater and pollutant runoff into a nearby lake, according to a recently released seven-year performance study.

Typically used for parking lots and sidewalks, porous paving material allows stormwater to filter through the pavement and an aggregate base into the soil rather than run off the pavement and drain into storm sewers.

Shoreview bucked convention by using pervious concrete in a traffic application — low-volume, low-speed roads in the Woodbridge neighborhood near Lake Owasso. The city thought pervious pavement could help meet community sustainability goals and federal clean water regulations by reducing pollutants in waterways and groundwater while keeping water safely off driving surfaces.

Traditionally, pervious concrete hadn’t been used for roadways because engineers didn’t consider it strong enough for traffic (this and other projects have now demonstrated its application for low-volume roads like neighborhood streets). The impact on ride quality, tire-pavement noise and filtration was also not well understood, particularly in cold climates with freeze-thaw cycles like those in Minnesota.

Pervious concrete also presented a maintenance challenge: Organic debris, sand and other grit can clog the pavement’s pores. Periodic vacuuming is required to maintain the intended flow of water through the pavement. Concerned about how best to maintain the pavement and interested in tire-pavement noise levels and filtering performance, Shoreview, MnDOT and the Local Road Research Board monitored the Woodbridge roadways for seven years.

Installation and Evaluation

Shoreview replaced 9,000-square -feet of asphalt roads with 7 inches of pervious concrete over 18 inches of coarse aggregate base; near the lake, highly drainable sand served as the base. About twice each year for five years, researchers tested sound absorption, water infiltration and ride quality one day after the pavement had been vacuumed. In 2015, they repeated these tests without vacuuming the day before.

The pervious pavement performed well in filtering stormwater. By 2012, at least 1.3 acre-feet of water had filtered through the pavement and ground, and by 2015, nearly 2 acre-feet of water had filtered through the surface—all of which would otherwise have run directly into Lake Owasso.

Water infiltration and sound absorption rates were higher than traditional concrete, although rates declined over time because organic material continued to clog pavement pores despite vacuuming twice a year.

Conclusions

Initial construction of the pervious concrete streets and stormwater filtration system was slightly more costly than construction of comparable asphalt pavement with culverts. Life-cycle costs, including projections of maintenance costs over 15 years, however, showed somewhat lower costs for pervious pavement. While the pervious concrete pavement may require diamond grinding after 10 years, monthly vacuuming could make this unnecessary. Asphalt pavement would typically require a mill-and-overlay at year 15, and culverts would require periodic cleaning.

Additional benefits of the pervious pavement system that were not included in cost calculations—but were clearly significant—included complying with the federal Clean Water Act, recharging groundwater and avoiding direct pollution of Lake Owasso. Shoreview’s investment in pervious concrete has paid off economically and environmentally.

For additional information about this line of research, see these resources:

 

 

 

Environment, Maintenance Operations

Carver County Evaluates Pickle Brine for Ice Control

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Like many snow- and ice-control professionals, Carver County Public Works maintenance operations staff are searching for new options to reduce the amount of chloride that reaches our waters from road salt operations. Using food production byproducts such as pickle brine are among the alternatives maintenance staff have been exploring.

Carver County regularly uses salt brine as part of their winter maintenance operations, which has become a widely accepted practice for controlling snow and ice. In the right situation, salt brine can be a more effective alternative to traditional road salt. An opportunity to obtain a free supply of sodium-rich pickle juice from a nearby canning facility seemed like a natural candidate worthy of consideration as a source of brine for county anti-icing and de-icing operations. In addition, recycling the pickle brine could reduce the amount of the waste byproduct.

The Carver County Public Works Department began testing samples of the pickle juice in 2016 with some encouraging results. But further testing showed the brine from the pickle cannery had variable salinity and pH levels that could damage maintenance equipment. Given the variables involved, staff determined it would be difficult to manually control the manufacture of the brine into a usable liquid. VariTech Industries recommended purchase of the Brine Boss, an automated brine blending system to manufacture the 23.3 percent brine solution needed for effective ice control operations. In addition, staff found adding potassium hydroxide to pickle brine neutralizes the pH level.

Carver County staff received a grant through the Local Road Research Board‘s Local Operational Research Assistance Program (OPERA) to help purchase the brine making system and support further research into the viability of using pickle brine in winter maintenance operations. Staff also restored an old VariTech 600 brine maker obtained from MnDOT for the project.

After extensive testing and analysis, VariTech engineers and Carver County staff concluded that pickle brine acquired from the cannery had to be exactly the same (salinity, vinegar content, and sugar content) for each and every batch or the system sensors would fail. But it turned out that the pickle brine supplier could not provide chemically consistent batches, and the VariTech system was unable to produce a consistent blend of 23.3 percent brine solution using pickle brine. As a result, Carver County staff determined they were unable to continue using pickle brine for snow and ice control.

Nevertheless, this project benefits other agencies considering the use of food production byproducts. The Carver County project demonstrates that there can be an alternative anti-icing product. As technology continues to advance, Carver County may revisit the use of pickle brine as a viable snow- and ice-control option.

For additional information about the project, check out these resources:

Environment, Materials and Construction

Managing Stormwater Runoff with Recycled Peat and Taconite Tailings

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Researchers have found that peat has high potential to replace commercial compost in MnDOT’s standard bioslope and bioswale design for roadside ditches, and that taconite tailings performed comparably to the sand currently specified in MnDOT designs, with the additional benefit of removing phosphates.

Finding alternatives to commercial compost and sand for use in bioswales will help MnDOT meet regulatory requirements for stormwater runoff, while reducing the costs and environmental effects of transporting and storing these materials.

“The results of this project will very much facilitate the development of green infrastructure by reducing its cost to MnDOT and Minnesota local agencies, helping them to do more with less,” said Dwayne Stenlund, Erosion Control Specialist, MnDOT Erosion Control and Stormwater Management.

What Was Our Goal?

The objective of this project was to evaluate peat and muck excavated from construction activities, taconite tailings from area mining operations, and other stormwater quality filter media for use in bioswales and bioslopes along Minnesota highways. Laboratory and field tests of these products would examine their capacity to absorb water, retain pollutants and support plant growth to determine if they are beneficial and practicable in these designs.

What Did We Do?

2017-46-p1-image
For field tests, researchers created small plots using either peat or  compost mixed with native soil.

Researchers began by conducting a comprehensive literature review on the use of bioslopes and bioswales as stormwater treatment best management practices. Then they collected peat and muck near a highway construction project, as well as locally sourced sand, compost, taconite tailings and commercial peat.

These materials, as well as various combinations of materials, were used in laboratory experiments to determine how well they:

  • Absorbed water, using a falling head test to measure saturated hydraulic conductivity, which indicates the rate at which water infiltrates a material.
  • Retained pollutants, using leaching experiments to quantify how well they removed copper, lead, zinc, nitrate and phosphate.
  • Sustained plant growth, using bioassays and greenhouse studies.

Finally, researchers conducted pilot field tests on three plots containing a 50/50 percent peat and sand mixture, and another three plots with a 50/50 percent compost and sand mixture. Between April and August of 2017, they monitored water infiltration, discharge water quality and vegetation establishment for these sites.

What Did We Learn?

“Ultimately, a combination of peat and taconite tailings will compare favorably with current MnDOT specifications for bioslope and bioswale design,” said Kurt Johnson, Research Fellow, University of Minnesota Duluth Natural Resources Research Institute.

Researchers found that peat has a strong potential for replacing commercial compost in MnDOT’s standard bioslope and bioswale designs, and that taconite tailings also performed comparably to the sand currently specified in these designs. However, muck has little potential to replace commercial compost or peat due to its low permeability, poor infiltration and filtration properties, and lack of support for plant growth.
Results for the three properties of interest follow:

  • Infiltration rate: While muck had an unacceptably low hydraulic conductivity, peat performed at least as well as compost, and taconite tailings as well as sand. Pilot tests showed that a 50/50 mix of peat and taconite tailings had a similar water storage capacity to a 50/50 mix of compost and sand.
  • Pollution retention: Muck absorbed only 50 percent of metals; salvaged peat, commercial peat and compost performed well, absorbing more than 80 percent. However, only taconite tailings showed the potential to remove phosphate. None of  the materials removed nitrate.
  • Plant growth: Mixtures of compost or peat with sand or taconite tailings all performed well in providing a viable substrate for plant growth. Mixes containing compost performed the best in plant growth trials. Muck was difficult to mix with any other material, and its value for plant growth was minimal. Greenhouse study results showed no difference between sand and taconite tailings in their effect on plant growth response.

What’s Next?

In a second phase of this project, “Development and Regionalization of In Situ Bioslopes and Bioswales,” MnDOT will conduct further laboratory tests on alternative materials for bioslopes and bioswales, and expand field tests to several sites in Minnesota that have been constructed using these materials. Researchers also recommend the development of specifications and detail drawings for the use of these materials.

This blog pertains to Report 2017-46, “Comparing Properties of Water Absorbing/Filtering Media for Bioslope/Bioswale Design,” published November 2017.

Bridges and Structures, Environment

Using Mussel Spat Rope to Facilitate Small Fish Passage in Culverts

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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.

Environment, Maintenance Operations

Research Provides Foundation for Chloride Mitigation Efforts

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The accumulation of chloride in our waters has become a widespread concern. In a recent study sponsored by MnDOT and the Local Road Research Board, researchers measured the transport and accumulation of chloride from road deicers in a metro-area watershed. The findings revealed a greater infiltration of chlorides into soil and subsurface waters than previously assumed.

“The results of this research provide us with knowledge we did not
have before,” says William Herb,a research associate with the University of Minnesota’s St. Anthony Falls Laboratory and the study’s principal investigator. “It will help investigators and policymakers explore ways to capture chlorides and mitigate their damaging environmental effects.”

Road salt (sodium chloride) is used in most states that experience snow and ice, with growing impact. For example, chloride levels in some lakes and streams in the Minneapolis–Saint Paul metro area exceed state and federal water quality
standards, and a recent study showed that levels in more than one-quarter of shallow groundwater wells in the metro were above drinking-water taste standards.

“This is a real concern because even in low concentrations, chloride can be lethal to sensitive plants and some aquatic species, and many of our lakes, wetlands, and streams show acute or chronic levels of chloride,” Herb says.

To learn how chlorides from road salt deicers are transported in urban watersheds, researchers installed field instruments at eight sites in a Roseville watershed. They monitored water and chloride levels nearly continuously over three winter seasons; this included runoff directly from sources (roads and parking lots), transport in ditches and sewer networks, and retention in and release from detention ponds and wetlands. Computer modeling was used to generalize results.

2017-50-p1-image
This drain along State Highway 36 was one of the roadway runoff discharge sources used in the study.

Overall, the team observed substantial chloride retention via infiltration to soils and groundwater. For example, monitoring the runoff from a vegetated highway ditch showed that more than 95 percent of the chloride applied to the highway infiltrated
from the ditch into the soil, and less than 5 percent was exported from the site in surface runoff. “Interestingly, substantial chloride export from the ditch was observed in November rainfall runoff prior to application of any new road salt for the upcoming winter, suggesting long-term storage in soils and groundwater in and near the ditch,” Herb says.

Researchers also found that winter rain-on-snow events and the first major
prolonged thaw each season moved surface chlorides most effectively into the watershed.

The research team then used the data and modeling to examine potential strategies for reducing or mitigating the spread of chloride, including capturing low flows, seasonal runoff capture, and capture based on salinity.

Wayne Sandberg, deputy director of the Washington County Department of Public Works, chaired the study’s technical advisory panel. “Based on this research, we now know that deicer chemicals are staying in the soil and moving in the watersheds, and this should change how we manage ice and snow control,” he says. “The next questions are what can we do with that knowledge and what changes can we make.”

This article originally appeared in CTSs Catalyst Newsletter, March 2018 and pertains to Technical Summary 2017-50TS. The full report, “Study of De-icing Salt Accumulation and Transport Through a Watershed” 2017-50, published December 2017 can be accessed at mndot.gov/research/reports/2017/201750.pdf.

Bridges and Structures, Environment

Darkness in Box Culverts Not a Likely Barrier to Topeka Shiner

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Darkness box culverts does not present a complete barrier for southwestern Minnesota fish species, according to a new MnDOT study. The findings will reduce the cost and  delay of future box culvert replacement projects.

“This research will allow MnDOT to save both time and money when replacing other box culverts in southwestern Minnesota by eliminating the need for a fish passage study for each one,” said Scott Morgan, Principal Hydraulics Engineer, MnDOT District 7.

The research project is one of several undertaken by MnDOT and the Local Road Research Board to better understand fish passage (more at mndot.gov/research), and ultimately develop a Minnesota culvert design manual for accommodating aquatic species.

What Was Our Goal?

In this study, researchers developed several objectives in their efforts to assess the effect of low light levels on fish passage through replacement box culverts. As part of this effort, they wanted to determine typical light levels in the replacement culvert and other box culverts in the region. They also sought to determine if the Topeka shiner and other fish move through culverts in the same numbers they pass through control areas in the same stream, and whether light levels affect frequency of movement. Finally, if a barrier is determined, researchers sought to design or recommend a method for mitigating light in the culvert.

What Did We Do?

In the field, researchers characterized light in long box culverts (at least 8 feet by 8 feet) by collecting many light levels with a light meter at the water surface within the three culverts and at control reaches. They also measured light levels within the water column to characterize the light conditions a fish would experience.

To determine whether Topeka shiners passed through culverts in similar numbers as through control reaches of the same stream, and whether light levels affected their passage, researchers employed a mark-and-recapture process. They caught fish upstream and downstream from the culverts or control reaches, marked them with an identifier indicating where they were caught and released, and then resampled to see where fish moved. They also noted other culvert features that could affect passage, such as water depth and velocity.

Image of fish tank.
In light manipulation experiments at the St. Anthony Falls Laboratory, Topeka shiners and fathead minnows were allowed to choose channels to swim along. The degree of shade in one channel was adjusted from light to deep shade.

To control for confounding variables that could affect fish movement, a laboratory study measured Topeka shiner preference for light or dark channels. Researchers used a 25-foot-long double channel box with water diverted from the Mississippi River. Fish could choose to swim along light or shaded lanes as they preferred in this light manipulation experiment.

What Did We Learn?

Although there has been increasing concern over the potential for culverts to create behavioral barriers for fish and other organisms, this was the first study that quantified these behavioral effects for fish passage. Light levels in large box culverts were not identified as a potential barrier to the fish communities present in southwestern Minnesota. Two out of the three culverts monitored showed reduced fish passage compared to the control reaches; however, fish—including Topeka shiners—were able to pass through all three.

The longest and darkest culvert had the greatest difference in movement between the culvert and the control, but this variation could not be attributed solely to light levels. This finding was supported by experiments at the St. Anthony Falls Laboratory, where fish that could select either a shaded or lighted channel showed no avoidance of the shaded channel regardless of the shading level.

The light measurements in three culverts yielded an extensive data set that can be used to model light levels through culvert barrels. Light levels at the water surface depended on the culvert entrance, dimensions, construction material, orientation and elbows, while light levels in the water column were also affected by turbidity.

What’s Next?

The conclusions of this study apply only to Topeka shiners and other small warm water fish species, and to large box culverts like those studied. Additional research is required to investigate possible barriers created by smaller, darker culverts to light-sensitive fish species and the interactions between light and other variables such as velocity.

This post pertains to Report 2017-44, “Culvert Length and Interior Lighting Impacts to Topeka Shiner Passage,” published November 2017. The full report can be accessed at mndot.gov/research/reports/2017/201744.pdf.

Environment

Establishment and Care of Salt-Tolerant Grass on Roadsides

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Kentucky bluegrass, the grass species that MnDOT typically uses for roadsides, was sensitive to salt; many installations could not tolerate winter deicing salts and died. Research on salt-tolerant grasses begun in 2009 resulted in MNST-12, a grass mix of fine fescues (with 20 percent Kentucky bluegrass for sod cutting, transport and installation stability) that is more salt-tolerant. MNST-12 was installed at many roadsides sites but by 2013, many MNST-12 installations were not thriving. Research into the reasons for these failures and the ways to best establish and care for MNST-12 revealed that this salt-tolerant grass mix requires a different planting and irrigation regimen than the standard MnDOT protocols that had been used for decades on Kentucky bluegrass. When installed as seed, MNST-12 should be planted in August or September; when installed as sod, it can be laid between May and November if sufficient irrigation is available. MNST-12 roots slowly and needs a particular irrigation regimen in early stages. Moisture replacement of 60 percent of its evapotranspiration rate is sufficient to promote establishment.

“The [highway] construction critical path for program delivery rarely includes a biological requirement for establishing vegetation. For salt-tolerant fescue grasses, planting dates and irrigation regimens matter,” said Dwayne Stenlund, Erosion Control Specialist, MnDOT Office of Environmental Stewardship.

“Basing irrigation approaches on evapotranspiration could reduce water consumption and, ultimately, the cost of establishing areas by sod,” said Eric Watkins, Professor, University of Minnesota Department of Horticultural Science.

Failed Kentucky bluegrass along a roadway
Because of its poor salt tolerance, Kentucky bluegrass has failed at many roadside sites in Minnesota.

What Was the Need?

Minnesota has more than 24,000 acres of green, grassy roadsides, ranging from street terraces to Interstate high-way medians. These roadside environments have many stressors, including heat, drought, insects, weeds, traffic and salt.

MnDOT has traditionally used Kentucky bluegrass for turfgrass, but its poor salt tolerance has resulted in many failed installations. Seed and sod research begun in 2009 produced MNST-12, a salt-tolerant grass mix of mostly fine fescues. By 2013, however, many roadside installations of MNST planted under MnDOT’s standard turf care protocols had failed and the reasons were unclear.

Replacing an acre of failed sod costs up to $25,000. MnDOT needed to learn why the turf failed and find the right methods to establish and care for salt-tolerant grass.

What Was Our Goal?

Researchers sought to assess installations of MNST seed and sod across the state to determine the planting and care practices that resulted in successful establishment or in failure. They also wanted to identify best practices for salt-tolerant turf establishment and care.

What Did We Do?

The study had two phases. In the first phase, researchers identified 16 roadside sites located throughout the state with salt-tolerant turf that had failed or performed poorly. They assessed these sites from July 2013 through 2014, and gathered detailed information about the sites from MnDOT, landscape contractors, sod producers and weather data sites. Information included date and time of installation, sod or seed used, temperature and precipitation at installation, and irrigation and mowing protocols. At each site, researchers also took measurements of ground cover, salinity, temperature, moisture content, surface hardness and depth of soil to top of curb. Soil samples were tested for pH, available phosphorus and organic matter.

Beyond variations in soil moisture, it was unclear whether any other soil aspect promoted the success or failure of site turf. Homeowners at various locations suggested that installation date and supplemental irrigation might have influenced a site’s success.

In the second phase of the study, investigators identified the best management practices for MNST by examining three factors that could influence turf performance:

  • Use of soil amendments during establishment. Researchers examined the effects on MNST performance of seven types of soil amendments, from slow-release fertilizers to various composts, used in trial plots.
  • Timing of seed and sod installations. Subsections of large trial plots at St. Paul and Blaine, Minnesota, were seeded or sodded monthly starting May 1 through Nov. 1. The watering regimens followed MnDOT’s 2014 specifications.
  • Post-installation watering regimens. Researchers planted sod plots of MNST and Kentucky bluegrass in a controlled outdoor area using an automatic sheltering system that protected the test areas when it rained. Irrigation was carefully controlled to test seven watering regimens. Researchers studied turf cover, root growth and shear strength of grasses at the sites.

What Did We Learn?

Soil amendment treatments had little effect on turfgrass performance, whether the plots were seeded or sodded.

MNST planted as seed cannot tolerate the heat and frequent drought conditions of Minnesota’s summers during establishment. Seeding should therefore only occur in August and September. Sod may be laid between May and November, provided there is adequate irrigation.

MNST differs biologically from Kentucky bluegrass and has different watering needs. Root development occurs more slowly and requires a longer period of irrigation during establishment, thriving with moisture replacement between 60 and 100 percent of the evapotranspiration rate. With adequate water, MNST establishes well.

MNST should not be mown until roots are established several inches into the soil profile. Drought-stressed turf should not be mown.

What’s Next?

Revisions to MnDOT’s specifications and guidelines are needed. In addition, MnDOT will need to adjust its previous recommendations for watering MNST-12 sod to ensure a successful installation. Further, guidelines for designers and inspectors must be updated. MNST is a different grass community than Kentucky bluegrass–dominated sods: The perception of what “success” looks like must be changed, and this change can be best accomplished through images. New methods of irrigation will need to be devised and implemented. Providing water only as the plant needs it could result in considerable savings in water and labor over time. Additional studies related to best management practices are pending.

This post pertains to the LRRB-produced Report 2017-31, “Best Management Practices for Establishment of Salt-Tolerant Grasses on Roadsides,” published July 2017.