Tag Archives: sediment

Sediment Control Log Guidance for Field Applications

Researchers tested sediment control logs in the lab and in the field to determine the relative filtration capabilities of these devices. They also developed design guidelines for correct selection and contributed to ongoing educational efforts. 

What Was the Need?

Whenever MnDOT or its contractors engage in construction, maintenance or other projects that substantially disturb the soil at a project site, they are required to use practices that reduce sediment discharge from the site when it rains. Sediment control methods are used as perimeter barriers around stockpiles, for inlet protection, as check dams in small drainage ditches and also along natural waterways such as streams, ponds or wetlands. 

A commonly used method is the sediment control log (SCL)—a linear roll constructed with an outer sleeve of varying permeability that is filled with natural biodegradable infiltration materials such as straw, coconut fiber (also known as coir), compost or rocks. MnDOT’s SCLs range from 6 to 9 inches in diameter and up to 30 feet in length.

While MnDOT has used SCLs extensively for many years, these devices often fail because their performance is not well-defined or understood. SCLs are also frequently installed incorrectly or in inappropriate locations. Because SCL use represents a substantial cost to the agency, MnDOT sought to learn actual performance parameters as well as optimum locations and installation methods. 

What Was Our Goal?

The goal of this project was to improve practitioners’ ability to select the appropriate SCL for a specific purpose and location. To achieve this goal, researchers sought to:

  • Determine the hydraulic characteristics of SCLs—how SCLs constructed from different encasement fabrics and internal media allow the passage of water. 
  • Evaluate the sediment removal efficiency of these SCLs and the effect of trapped sediment on their hydraulic characteristics.
  • Develop design guidelines for selecting SCLs based on log materials and the characteristics of the watershed where they will be installed. 
  • Organize the selection guidelines into a format that can be used by field practitioners for amending or upgrading the device. 

“This study compared the sediment filtration capabilities and effective life cycles of a range of sediment control logs. This new knowledge will allow us to reduce costs in all areas of sediment control log use and more effectively protect the environment.”

—Dwayne Stenlund, Erosion Control Specialist, MnDOT Office of Erosion Control and Stormwater Management 

What Did We Do?

First, researchers conducted a literature review of studies published from 1995 to 2013 that examined a variety of sediment control methods. 

Next, they determined the physical characteristics of 12 SCLs filled with diverse biodegradable media, ranging from straw; coconut fiber; wood fiber; wood chips; light, medium and heavy compost; and rock. Then they investigated the hydraulic characteristics of the SCLs, most importantly the volumetric flow rate through logs of various media, using the flume at the University of Minnesota’s Biosystems and Agricultural Engineering Laboratory. 

A sediment flume was constructed at this laboratory that researchers used to evaluate the sediment removal efficiencies and failure rates of a subset of five logs. The subset was selected to capture the range of hydraulic response representing a variety of log materials.

Researchers also examined field installations of SCLs in locations across the state to learn how SCLs were installed and, if failing, how they had failed.

A long, black sediment control log. Dried sediment is on top of a section of the log that traverses a shallow, eroded ditch. The log is held in place with two wooden stakes on the downslope side.
Overtopping occurred at this failed SCL installation, indicated by the dried sediment on the log. 

Finally, they produced two SCL selection tools and developed training materials about SCL use. 

What Did We Learn?

From the literature review, researchers reviewed seven laboratory studies and nine field studies examining a wide range of sediment control methods. They found no studies similar to this project that compared different kinds of SCLs for their sediment removal efficiency, life cycles and appropriate siting. 

Researchers investigated the physical characteristics of 12 SCLs, including diameter, density and percent volumetric pore space. They conducted material size analysis and other tests to determine saturated moisture content, capillary moisture content, saturated conductivity and other relevant hydraulic measures. Using results from the laboratory flume, they documented the flow rates of water through the SCLs. 

The physical characteristics of the 12 SCLs varied substantially. For example, densities ranged from 2.18 pounds to 18.5 pounds per cubic foot. Hydraulic characteristics, such as the amount of water retained and the rate of fluid flow through the medium, also varied widely. 

The subset of five logs tested for sediment removal efficiency showed how much sediment each log could filter at three flow rates and how much sediment buildup would cause log failure. These results combined with earlier hydraulic data allowed researchers to extrapolate the relative comparative longevity of different SCL media and to develop two SCL selection tools: one for ditch checks and one for perimeter control. The tools will guide practitioners to select the correct SCLs using watershed area, basin and ditch slope. Researchers also adapted the results of the investigations into a set of training materials for erosion control and stormwater management.

What’s Next?

The two decision tools will guide the selection of correct SCLs for particular locations. SCL training materials have already been implemented in the erosion control and stormwater management certification workshops. 

“Sediment control log failure is a worldwide problem. This research takes a substantial step toward a better understanding of the parameters within which SCLs can be effective, clarifying with data their capabilities as well as their limitations.”

—Bruce Wilson, Professor, University of Minnesota College of Science and Engineering

This post pertains to Report 2019-23, “Sediment Control Log Performance, Design and Decision Matrix for Field Applications,” published May 2019. Visit the MnDOT research project page for more information.

Tailgate Test Kit Speeds Up Flocculant Choice to Reduce Sediment in Runoff

The Tailgate Test Kit quickly and easily identifies flocculants that reduce turbidity in construction stormwater discharge. The mobile test setup efficiently determines which of the many available products works best for a particular construction site. In this study, 13 product combinations were tested. A short list of five tests was developed, as well as worksheets to aid in calculating the amount of flocculant needed and developing scale-up procedures.

“The Tailgate Test Kit is a cost-effective innovation that will help us determine the flocculant and quantity of product to use in the field and in real time,” said Dwayne Stenlund, Natural Resources Program Coordinator, MnDOT Environmental Stewardship.

“It’s important to add to the body of knowledge in this area,” said Joel Toso,
Senior Water Resources Engineer, Wenck Associates, Inc. “The Tailgate Test Kit is already being used in the field to help both contractors and maintenance workers make decisions.”

What Was the Need?

Stormwater runoff from construction sites often carries sediment from soil erosion, causing the water to become cloudy or turbid. Federal, state and local stormwater regulations prohibit construction sites from discharging water that is too turbid into the environment. Instead, the runoff must be sent to ponds to allow the sediment to settle to the bottom of the pond. The remaining clear effluent may then be discharged from the site.

A worker collects a sample of construction site stormwater runoff in a plastic-lined settling pond while another looks on.
Testing stormwater sediment levels at the construction site allows field crews to begin treating turbid water quickly.

The chemicals in flocculants speed up the sediment settling process by causing the sediment particles to clump together and fall to the bottom more rapidly. A number of flocculating agents are commercially available. The most effective agent for a specific situation is generally deter-mined by testing various flocculants with water samples in a lab. This selection process usually takes one or two days. Only after the appropriate flocculant is selected can the entire pond be treated.

To speed up this process, MnDOT has developed the Tailgate Test Kit, a series of tests that can be conducted in the field to determine the most effective flocculant, as well as the correct amount, for a specific construction site and soil type. What used to take a day or two to process in the lab now can be accomplished by field crews in an hour or two on the tailgate of a truck, enabling workers to begin treating the ponded turbid water much more quickly.

What Was Our Goal?

The overall goal of this study was to build upon the findings of several recent research projects, including “Flocculation Treatment BMPs for Construction Water Discharges” (2014-25), by developing and improving field methods to reduce total suspended sediment from construction stormwater runoff. A specific aim was to create a method for work crews to test water samples in the field using a mobile test toolkit that contains flocculants identified in previous research. Other goals included determining the most effective amount of the flocculant needed, developing the calculations needed for scale-up once the best product is identified and implementing a test for residual unreacted product.

What Did We Do?

To identify a variety of flocculant product types to evaluate with the Tailgate Test Kit, the research team summarized stormwater best management practices from the literature and from other departments of transportation. Since the effectiveness of product types varies depending upon soil and sediment types and environmental conditions, researchers conducted 13 tests of nine flocculant products (alone and in combination) taken from five distinct product classifications: mineral, polyacrylamide, chitosan, bio-polymer and anionic polyacrylamide. They also tested water samples from eight locations in Minnesota to ensure a cross section of representative samples.

What Did We Learn?

Using the results from these tests, the research team developed a short list of five tests that could be conducted in the field and incorporated in the Tailgate Test Kit. The five tests represent a range of flocculant product classifications and reduce the time required to complete the tests.

The team also prepared worksheets with mixing and dosing guidance to help users identify the most effective amount of product to achieve the target turbidity goal. Finally, the team developed scale-up procedures to aid in using test results to determine full-scale dosing rates on-site and procedures for testing new flocculant products.

The researchers investigated four methods for testing residual flocculant to detect any unreacted product in a sample. A preferred method was not identified during the course of this research but would still be a desirable research outcome.

What’s Next?

Next steps for this research effort include field implementation and new product evaluation.

First, investigators recommend developing a training module and field guide for using the Tailgate Test Kit to encourage implementation of the mobile kit throughout the state. If users understand how it works and how to use the test results for scale-up calculations, they will be more likely to use it.

Second, the product list should be kept current by testing additional flocculant products. It may also be beneficial to create a category for flocculants on the MnDOT Approved/Qualified Products List.

Finally, methods to identify residual and unreacted flocculant product need to be developed. If excess flocculant product is used in field tests, the residues will eventually have to be collected and removed for disposal. Minimizing the excess flocculant used at construction sites is desirable.


This post pertains to Report 2017-32, “Tailgate Test Kit for Determining Appropriate Sediment Reducing Chemicals and Dose Rates,” published July 2017.