Extreme slopes over waterways call for permanent stability
Positioned on the banks above the Mississippi River, the charming city of Vicksburg, Miss., also is situated among the Big Black and Yazoo rivers and numerous pristine lakes. The region’s remarkable waterways qualify it as one of 41 destinations in the nation to host the U.S. Army Corps of Engineers, which strives to regulate waterways and protect aquatic resources and ecosystems. While the region’s blend of unspoiled waters and soaring bluffs form a landscape brimming with outdoor adventure, it also sets the stage for widespread erosion and sediment control challenges.
These issues became evident in Spring 2010, when the Vicksburg Parks and Recreation Department (VPRD) was tasked with developing a new 22-acre baseball park in time to accommodate the community’s active summer season. The site featured long, steep 2:1 and 1:1 slopes situated over several U.S. Army Corps-protected environmental areas—from small creeks to the Mississippi River—creating a need for permanent stabilization to prevent sediment leakage. The approaching rainy season added an element of urgency to establish vegetation and stabilize the slopes before the onset of heavy rains.
No Blanket Solution
The VPRD selected Clear River Construction as the general contractor to spearhead the project. The site’s initial evaluation called for straw erosion control blankets, designed to provide immediate erosion protection and vegetation establishment assistance. Further slope assessment, however, revealed that blankets alone would not provide suitable, long-term stabilization for the site’s extreme conditions, with the 1:1 and 2:1 slopes measuring 100 and 200 ft long.
Added analysis ruled out blankets entirely, and the project team ultimately decided to apply an erosion control product that was capable of establishing dense vegetation in a quick and cost-effective manner. The site’s engineering firm opted for a spray-on high-performance hydraulic erosion control product (HECP), selecting Tensar Intl. Corp.’s straw and reclaimed cotton plant material-based North American Green HydraCX2 Extreme Slope Matrix.
Clear River Construction consulted with Terry Jones, vice president of Geo-Products and distributor of erosion control products in Madison, Miss., to determine the most efficient application techniques to successfully complete the job.
“Since efforts to stabilize the site’s slopes were taking place at the height of Vicksburg’s rainy season, we knew we’d only have one real shot to apply the HydraCX2 HECP fast and heavy,” Jones said. “The site’s extreme slopes were challenging enough. The last thing we needed was the added obstacle of rainfall.”
Jones worked closely with the Clear River Construction team to administer a one-time application of the HECP to the slopes, using a 550-gal Turfmaker at a rate of 3,000 lb per acre.
Developed by Mulch & Seed Innovations LLC, Centre, Ala., a part of Tensar Intl. Corp., and Cotton Inc., the HydraCX2 Extreme Slope Matrix is an HECP made with mechanically processed straw fibers and reclaimed cotton plant material. The product contains proprietary performance-enhancing tackifiers that form a protective layer to help hold the soil in place and increase vegetation establishment.
“[It] contains beneficial nitrogen, hosphorus and potassium nutrients which, when made available to the soil, are important for plant growth. The high-performance HECP has been designed for water retention in the seedbed and to allow rainfall to trickle down into the soil through the porous interlocking matrix so that water and nutrients can be taken up by the roots of emerging vegetation,” said Wae Ellis, commercialization product leader for Tensar Intl. “It is our intention to avoid excessive water retention within the mulch layer, thereby encouraging the roots to become well established in the soil. It is also important that the material does not wick moisture away from the root zone during drought conditions.”
Featuring post-industrial waste from the cotton ginning process, the cotton plant material is a new reclaimed option that has proven to be an effective and sustainable alternative to virgin wood and recycled paper, which previously dominated the erosion control industry.
In spite of the installation crew’s best efforts to avoid challenges from Mother Nature, the site received 1 in. of rainfall during the brink of treatment. Jones and the contractor said they anticipated major glitches.
“We were pretty worried about how the slopes would turn out, given the amount of rain the site endured,” Jones said. “However, to say we were pleasantly surprised would be an understatement. The [HECP] demonstrated incredible staying power and held the slope with virtually no soil loss. In our opinion, the unexpected rainfall helped to ‘seal the deal’ and set a positive tone for the remainder of the application process.”
Twenty-one days after application, the treated slopes held up with no erosion rills and demonstrated excellent seed germination, with many portions of the site ready to be mowed.
“When restoring soil and protecting against erosion in such extreme conditions, you can’t afford to apply the product more than once,” Jones said.
As the site matured, the slopes protected with the product established healthy vegetation that further increased the erosion control performance of the site. In contrast, untreated areas sprouted limited vegetation and demonstrated growth problems.