New systems monitor stormwater runoff from road construction sites

With higher turbidities, water temperature increases, the amount of available oxygen decreases, less light reaches aquatic plants, and sediment accumulation reduces water storage capacity—degrading the quality of our waters.

With higher turbidities, water temperature increases, the amount of available oxygen decreases, less light reaches aquatic plants, and sediment accumulation reduces water storage capacity—degrading the quality of our waters.

Transportation practitioners have new tools to help keep road construction runoff out of our waters, thanks to research from the University of Minnesota.

During a rainfall, eroded sediment from a site can be quickly transported to nearby lakes or rivers. Because of these negative impacts, the Minnesota Pollution Control Agency requires that the owner and operator create a stormwater pollution prevention plan explaining the practices to be used to limit sediment discharge from their sites.

The amount of eroded sediment in construction runoff is typically gauged using turbidity values, which measure the cloudiness of a fluid. However, the usefulness of measured turbidities rests upon how representative the data are of runoff at construction sites and the reliability of the relationship between turbidity and sediment concentration.

“There is extensive variability in the soils, slopes, compactions, and erosion control methods among construction sites, which increases the difficulty of calibrating turbidity probes and selecting sites for data collection,” says Bruce Wilson, a professor in the Department of Bioproducts and Biosystems Engineering and the principal investigator of the research. “In addition, the rapidly changing conditions of a construction site mean the long-term monitoring of turbidity from a single location throughout the construction project is rarely possible.” Along with these logistical challenges, turbidity monitoring also has the potential to be expensive.

The research project, sponsored by the Minnesota Department of Transportation, gives insight into overcoming the challenges and reducing the costs of turbidity monitoring at construction sites.The project had two main goals: investigating turbidity relationships for the conditions found at Minnesota construction projects, and developing protocols for the design and installation of cost-effective turbidity monitoring systems.

Researchers conducted lab tests to determine how the measure of turbidity relates to the actual sediment concentration in the runoff. In addition, they evaluated five different turbidity sensors on five different soil textures to determine how soil texture and probe configuration affected turbidity readings.The team them measured the turbidity of runoff at two construction sites. These field studies were used to develop two different turbidity monitoring systems.

“In the future, the two turbidity monitoring systems developed for this study can be used to help transportation agencies cost-effectively monitor the turbidity of construction site runoff,” says John Gulliver, a professor in the Department of Civil, Environmental, and Geo- Engineering and the project’s co-investigator.

Read more in the December 2014 issue of CTS Catalyst.

Posted in Construction, Environment, Transportation research

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