If you are dealing with conditions that are far from ideal such as erosive soils, steep, long slopes you need an alternative for sediment control and the right steps before construction begins. A construction team ran into these conditions in Sioux City, Iowa, and came up with a way to address the issues and find a solution. It included applying good planning, incorporating a great design, and selecting an impressive product. They were able to create a superb erosion control and revegetation project.
A diversified project team was put together to handle the challenges that laid ahead. They cut slopes after the construction of a store and parking lot. The slopes were approximately 100 ft long. Most of the slopes were created at a slant of 2H:1V but some were even steeper.
Jered Morris, from Olsson and Associates in Lincoln, NE, was the project engineer on the site who was given the task to design an erosion and sediment control plan. Colorado Structures out of Colorado Springs, Colorado, was the primary contractor on the project and K & L Construction, out of Bluff, Iowa, was the sub-contractor to take care of the excavating activities. While the team was made up of people from different locations, they all had the same goal to create a successful erosion control and revegetation.
The National Pollution Discharge Elimination System (NPDES) Phase II requires all sites of one acre or larger to follow the correct permitting process. Also, before the land could be disturbed, a Storm Water Pollution Prevention Plan (SWPPP) must be created for the site. The plan outlined how to successfully control soil erosion and stormwater runoff by laying out where the cut slopes would be located and how they would be protected from soil erosion.
Carrying Out The Plan
Before carrying out the plan, the project team needed all the appropriate permits in place and all needed to be approved. The excavation and stabilization of the cut slopes started in the fall of 2002. Early on in the planning stage, there were concerns about the long length of the slopes. To address the problem, Morris decided to break up the length of the slope with benches. Three paved and guttered benches were constructed on the hillside at right angles to the slope in order to collect and redirect anticipated stormwater runoff. The fourth gutter system was constructed across the base of the slope to collect and redirect runoff before it could reach the parking lot.
Erosion Control Measures
The erosion control measures were the next steps in the plan to protect the slopes. The project was designed with a mat of composite and reinforcement for TRM, integrating a long-term biodegradable matrix with permanent components.
After speaking with representatives from American Excelsior Company (AEC), Morris decided to use a different product. John Merthan, Territory Manager, and Tony Johnson, National Research Director, got together and evaluated the project conditions. Curlex® Enforcer® QuickGrass® was suggested by the team for the site. The TRM product contains dyed-green excelsior wood fibers and heavy-duty UV-stabilized polypropylene netting in the blanket-like configuration that offers a surface cover to reduce erosion and increase the establishment of vegetation. The product was chosen for the project due to the following facts:
Foreseen hydraulic forces would not need the performance degree of the original product.
The biodegradable wood fiber element improves vegetation establishment better than long-term biodegradable matrices.
The cost for erosion control materials would be reduced while providingequal or better results.
The green color of the product would provide a finished look until vegetation is established.
The project team liked the product because it offered permanent reinforcement for vegetation.
Installing Erosion Control Products
Six inches of topsoil material was spread across the graded slopes to help resist the very erosive native loess soils before the erosion control products could be installed. All disturbed land was seeded with native grass and wildflowers. On top of that, oats were included in the seed mixture to serve as a quick cover. An eight-man crew was brought in to install the erosion control products. The crew started their protection process at the top of the slope then worked their way down to the base of the slope. Almost 50,000 yds of composite TRM material was installed to protect the slopes at the project.
Nature’s Bump In The Road
The project moved along at an even clip but nature always has a way to wake us up and teach us something. The site experienced heavy rain shortly after the benches were constructed and the erosion control material was installed. The system design withstood two different heavy storms that produced approximately 3 inches of rainfall followed by two more inches. Then the third rain storm dropped almost four inches which did cause a minor problem at the site. The storm drains on the benches had been covered because excavation was still taking place on the slope. The largest storm hit before the covers could be removed from the drains. Water over-topped the bench and channeled into an erosion river. When the storm was over, only a small section of the 50,000-yard project was affected. An area approximately 24-feet wide by 20-feet long needed to be repaired. Merthan said they were all very fortunate the system held up the way it did. The conditions encountered were not planned but the design of the slopes improved the curveball nature flung at them.
A Successful Conclusion
To date, the system benches and composite TRMs are an aesthetic successful erosion control solution. The store and parking lot below the enormous slope are permanently protected thanks to the project team that devised and executed the perfect erosion and sediment control plan.