Jul 10, 2020

Keeping BMPs Afloat

When a road flooded in Lake County, Illinois, the importance of maintaining BMPs arose 

excavator

Green infrastructure features, commonly referred to as Best Management Practices (BMPs), are designed by regulators and engineers to hold storm water runoff created by an increase in impervious surfaces, such as roofs, roads and sidewalks. Typically, private landowners or neighborhood homeowner’s associations (HOAs) are responsible for managing them. Regardless of whose obligation, BMPs are only effective if they are well-maintained. 

Lake County, Illinois, located approximately 35 miles northwest of Chicago, is home to nearly 30 communities and villages in addition to 250 lakes. Residents are attracted to the area because of its accessible, protected, open spaces, hiking and biking trails, and water recreation. Because it provides a unique opportunity for an outdoor lifestyle with close proximity to a major metropolitan city, Lake County experienced a population growth of nearly 10% from 1990 to 2010 (US Census).

With this growth, came the development of more homes, shopping centers and businesses with impervious roofs and lots.

In addition to development, Lake County has lost approximately 55% of the wetlands that were present before settlement. The soils left behind when the last glaciers retreated about 10,000 years ago made the area attractive for farming. Once common practice, wetlands were drained or filled to make way for agriculture, eliminating their invaluable storm water storage function from the landscape.

As a result of these two factors, Lake County experiences frequent and severe flooding. A flooded road in one of Lake County’s villages provides an example of what could happen when BMPs are not maintained.

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The Challenge: Flood Road

North Barrington, Illinois, is a small suburban village with a population of just under 3,000 residents. Most of the homes rely on wells and septic systems for their water and waste.

Green infrastructure BMPs on private properties soak up water or carry it to the nearest stream or lake during heavy precipitation. As with many small villages, local government plays a storm water support role, notifying residents of BMP functionality problems and helping to identify solutions.

grassmere project area
Most homes in North Barrington, Illinois, rely on 

wells and septic systems for their water and waste. 

In 2014, following a significant spring snow melt and heavy summer rains, a major road in the village was flooded. A blocked drainage channel running through a wetland was causing the wetland to overflow onto the road. This storm water BMP had not been maintained for more than a decade and was filled with years of accumulated cattail duff. With the flooded road causing safety concerns for motorists, the village of North Barrington stepped in to help the HOA with emergency BMP maintenance.

The Storm Water Solution

The solution to restoring flow through the wetland was to dredge the cattail material that was blocking the channel. However, the channel was in the middle of a saturated wetland where heavy dredging equipment would sink. 

U.S. Army Corps of Engineers permit requirements necessitate frozen ground or the use of construction mats to support the weight of the traditional dredging equipment. The project cost nearly $200,000. It seemed the only option to unclog the channel was to wait for freezing conditions. After two years of warm winters, the village knew it needed a different solution and turned to the County Stormwater Management Commission.

The county recommended working with Integrated Lakes Management (ILM.) The solution called for an amphibious excavator, a marsh buggy and a sled.

bmp maintenance
The solution to restoring flow in the wetland was to dredge the cattail material blocking the channel. 
grassmere south section
It took two weeks of excavation to remove about 300 cubic yards of material from the channel. 

An amphibious excavator has wide tracks and sealed pontoons that allow it to perform dredging while staying afloat in shallow waters. The excavator is self-propelled, using a hydraulic direct drive track system and can operate in demanding conditions. With ground pressure of 1.08 PSI (about half the amount exerted by a standing adult male), this vehicle can work in sensitive habitats without compacting the soils.

A marsh buggy is another amphibious unit. It serves as transportation and has a platform for running various auxiliary attachments, such as backhoes and cutters. In this case, the marsh buggy pulled a sled that carried excavated material out of the wetland and up onto dry ground.

The sled is designed with a wide, flat bottom that glides over the substrate while holding up to 3,500 pounds of material. Outfitted with a hydraulic lift, one side of the sled can be raised so that the heavy, saturated material can slide off to unload once on land. 

By using amphibious equipment, the project proposal came in at a cost of 65% below the original estimate. A member of the HOA volunteered a 5-acre vacant lot for the dredged material to dry out and decompose. The fees for hauling and recycling this material would have added an additional 20% to the total cost of the project.

It took two weeks of excavating to remove approximately 300 cubic yards of material from the channel in order to restore flow.

Lesson Learned

Old infrastructure gives rise to challenges that must be addressed in a cost effective manner. All green infrastructure BMPs require regular inspections and maintenance to ensure they continue to function properly and yield expected water quality and environmental benefits, safeguard the public and protect a community’s financial investment.

In the end, proactive periodic maintenance will be less expensive than reacting to problems caused by years of neglect. If a problem does arise, consider creative solutions to ease challenging circumstances at a reasonable cost.  

About the author

Lisa Woolford is vice president of green initiatives for ILM. Woolford can be reached at [email protected].

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