Working With Nature to Solve Eroded Creek Bank
By: Matt Welch, CPESC, CESSWI and Adam Dibble, CPESC-IT, CESSWI
Successful erosion control projects require a balance between reigning in Mother Nature and letting her be. When trying to deliver a solution that is efficient, timely and effective, it can be tempting to only focus on one side of the balancing act—reigning her in. In 2016, heavy rains ripped out erosion control blankets and left a creek bed severely eroded on a development site in Texas. The U.S. Army Corps of Engineers (USACE), Texas Commission on Environmental Quality (TCEQ), local Municipal Utility District (MUD) and developer, KB Homes, all had ideas on how to remediate the failed site. Many of the proposed solutions, while viable, focused on taming Mother Nature, rather than working with her to prevent future issues. As too many projects have experienced in the past, she can wreak havoc when told what to do.
Instead, the team selected a balanced solution that allowed the site to return to more natural conditions. Stuckey’s LLC partnered with Profile Products to employ the GreenArmor™ System—a green alternative to hard armor that offers a means of protecting high-discharge waterways and steep slopes. This solution allowed nature to punch through the creek at the levy break and reinforced the drainage path for inevitable heavy rain events. It combined nature’s intended path with man’s solutions.
Nestled on a floodplain in a wetland forest preserve, you’ll find the Houston suburb of Conroe, Texas. If you look at a map, you can easily carve the concrete city out from the nature that surrounds it. From 2015 to 2016, the U.S. Census Bureau named Conroe the fastest-growing city in the United States, expanding from 76,000 to 82,000 people in just one year—a 7.8 percent growth nearly 11 times higher than the national average. This influx of people also brought a flurry of construction to the temperamental ecosystem.
Conroe is prone to flooding if rainfall exceeds more than 9 inches in 48 hours. According to a 2008 flood insurance study by Montgomery County, Conroe has a 10 percent chance of receiving that much rainfall in any given year. But urban development is exacerbating that risk. A study by Texas A&M University found the entire Houston area lost almost 30 percent of its wetlands from 1992 to 2010—land that at one time could detain more than 4 billion gallons of stormwater. When Montgomery County experienced three consecutive 500-year floods from 2015-17, the increase in impervious surfaces made the flooding even worse.
In April 2016, more than 12 inches of rain fell in the Conroe area. In May, another 11 inches fell. It was one of the wettest springs on record for the Houston area. At the time, KB Homes was working on the Cayden Creek subdivision. As the name implies, the subdivision has a small creek running through it that eventually meets up with the San Jacinto River. As development in the subdivision began to increase, so did the amount of water that was being diverted into the creek.
In an attempt to stabilize the site and decrease runoff, contractors worked on vegetating 11 acres of the site with erosion control blankets for over a year. Despite several attempts, they couldn’t get vegetation to properly establish on more than two-thirds of the site, allowing sediment and runoff to flow into the creek.
When the 2016 spring storms hit, the strong water flow and lack of vegetation was too much for the creek to handle. The velocity of the water, and the swirling action it created, ripped out the blankets, washed away soil and blew out a 30-foot embankment on the creek. The resulting overflow moved into the amenity ponds and the channel. Sedimentation in the channel led to aggradation and decreased capacity, ultimately exposing the channel to a higher risk of flooding. Leaders on the development site weighed their options.
“All the time engineers are out here trying to reign in Mother Nature and we usually never win—Mother Nature is going to win,” said Matthew Skinner, a Market Development Manager at Profile Products. “I like this idea of trying to work with nature.”
Realizing that rebuilding the crumbled section of the creek would only lead to a failure in another spot, project leaders chose to reinforce the eroded bank, let the water flow at the break point into the creek, divert the water to a retention pond and then allow it to flow back into the creek downstream.
Using this plan, workers tried to reinforce the new break point with riprap and erosion control blankets. However, the concentrated flow during storm events was just too strong. The flowing water easily pushed the large rocks out of the way and deposited them more than 100 yards downstream.
After that initial failure, the project consultants contacted Stuckey Contractor Services, L.P. who partnered with Profile Products to create a solution that would establish sustainable vegetation and prevent erosion. The developers asked for results that would be stronger than the previously specified riprap and meet the standards of KB Homes, USACE and TCEQ. Each had their own requirements and guidelines that had to be met.
The USACE proposed pouring concrete in the area to bypass the eroded bank and create a pathway for storm water. While concrete could have satisfactorily completed the job, it was not the green solution the team was looking for and would have been expensive to construct. KB Homes was over budget and needed an affordable, aesthetically-pleasing solution that would solve their troubles and also satisfy their home owners. Meanwhile, the TCEQ looked at the project from an environmental standpoint. Stuckey’s LLC worked with Profile Products to show USACE and TCEQ how their environmentally friendly, hydraulically infilled Turf Reinforcement Mats stood up to the test of time on previous projects. With all agencies in agreement, the team got to work.
The Environmentally Friendly Solution
To start, Stuckey’s LLC conducted a soil test to determine why the site wasn’t growing vegetation. The analysis revealed that the soils had a high sand content, with less than 1 percent organic matter and a pH level higher than 8.5. The poor soil quality was likely the reason vegetation wasn’t establishing in earlier applications. The team knew they’d have to amend the soil to balance pH and increase the organic matter.
Stuckey’s LLC recommended using Profile’s ProGanics® Biotic Soil Media™ across the site in order to provide the organic matter and biological constituents that would help sustainably establish the vegetation the site needed. ProGanics is a topsoil alternative that accelerates the development of depleted soils and substrates with low organic matter, nutrient levels and biological activity. By working with regional seed and plant experts, the team developed a one-of-a-kind blend specific to the project site that would thrive in the amended soil.
With the soil amendment ready, Stuckey’s LLC then had to address the variety of erosion issues on the site. Starting with the area where the bank collapsed from the high hydraulic shear forces, Stuckey’s LLC selected Profile’s GreenArmor™ System 7010. The system works with a Futerra® 7010 Turf Reinforcement Mat (TRM) to provide a permanent, lofty and open matrix. This TRM consists of 95 percent open space and encourages growth. It is then hydraulically infilled with Flexterra® High Performance-Flexible Growth Medium®. Flexterra is designed with Thermally Refined® wood fibers and biodegradable interlocking fibers that firmly anchor seed to soil. When combined with the Futerra TRM, Flexterra provides resistance to shear force when the vegetation is establishing. It also incorporates micro-pore particles and biopolymers to optimize water and nutrient retention for enhanced establishment of vegetation. The GreenArmor System 7010 is designed to withstand shear stresses of up to 8 pounds per square foot and velocities of up to 14 feet per second.
“These were the most impactful parts of the project,” said Shane Stuckey, the Director of Business Development at Stuckey’s LLC “Getting ProGanics to establish vegetation on the high sand-content soil, then using GreenArmor to ensure the waters mixing and turning didn’t erode away that high velocity spot. The GreenArmor was constantly building sediment every time it would rain and prevented further erosion loss underneath it.”
Downstream, where the flow wasn’t as strong, Stuckey’s LLC used Flexterra on the floor of the drainage path. Above the peak-flow water line in the areas with the least extreme erosion issues, the team applied Profile’s ProMatrix™ Engineered Fiber Matrix™.
Mother Nature’s Approval
Within two months of application, the site was already establishing vegetation for the first time. Over time, silt moved through the GreenArmor System and became trapped in the grass, building a new natural shoreline for the creek nearly 6 inches thick. This eliminated the water quality issues the site had experienced downstream.
The real test came in 2017 when Conroe experienced one of the wettest years on record. The Cayden Creek subdivision saw more than 94 inches of rain, including a 60-inch deluge during Hurricane Harvey. After those rains, the developers worried the vegetation washed away and the banks had collapsed. But thanks to the thick vegetation reinforced by the Futerra TRM, the site held up. A large amount of silt built up in the ponds, rather than downstream in the creek. Stuckey’s LLC, who holds the maintenance contract on the site, was able to go in and dig out the silt without disturbing the natural creek or impairing water quality.
“The vegetation is thick and uniform and prospering,” Stuckey said. “Everything we did on that project was not what was originally planned. It was a major effort to get everyone involved, but using those methods is now the norm instead of coming in and fixing something that failed. I have engineers specify these products into the job now because of the results we got from this one project.”
Matt Welch is the technical and business development manager for Profile Products. He can be reached at firstname.lastname@example.org. Adam Dibble is the senior marketing and erosion control brand manager. He can be reached at email@example.com.
A version of this article first appeared in Storm Water Solutions.