Ninety-nine percent of counties in the United States have experienced at least one significant flooding event in the last 25 years, and there have been 33 flood events costing a billion dollars in the U.S. since 1980 according to the American Flood Coalition. Similarly, the EPA estimates that the average 100-year floodplain will increase 45 percent by the year 2100.

Due to this anticipated surge, engineers and agencies are taking a more proactive approach to mitigating flood hazards rather that addressing damage after it has occurred.  For example, FEMA is preparing to launch the Building Resilient Infrastructure and Communities (BRIC) program that will shift funds from reactive disaster spending toward investment in community resilience. With this proactive approach, sustainability and resiliency are becoming more important in flood mitigation project design. Particularly, an emphasis on solutions that provide low environmental impact while also achieving long-term performance and overall project success.

For more than two decades, Propex GeoSolutions has been engineering erosion control solutions that help improve water quality, support environmentally sensitive areas, and have lower environmental impact than traditional hard-armoring solutions. ARMORMAX®, its flagship solution, consists of High Performance Turf Reinforcement Mat (HPTRM) in combination with Engineered Earth Anchors to lock soil in place and provide immediate and permanent erosion protection for up to 75 year design life.

 

Tested and approved

The ARMORMAX system is not a new technology for the USACE. In 2005, following the aftermath of Hurrian Katrina, it was used for erosion protection of earthen levees against storm surge and wave overtopping.  Prior to installation, The USACE partnered with Colorado State University (CSU) to build a full scale wave overtopping simulator that tested erosion resistance of armoring materials for a 500-year resiliency based on HSDRRS design overtopping conditions. Testing showed that ARMORMAX increased resilience and durability of the levees, reinforced vegetation, and reduced the risk of breaching caused by storm surge and wave overtopping conditions.

Over two million square yards of ARMORMAX was installed on levees in the New Orleans area including Penn Levee, which later withstood wave overtopping conditions from both Hurricanes Isaac and Ike. Today, the USACE continues to use ARMORMAX to protect levees in New Orleans, but has also used the system on river levees and canals both for erosion control and slope stability.

 

Carbon footprint

Last year Propex became the only HPTRM manufacturer to have the carbon footprint of its product verified by an independent third-party organization.  One square meter of its HPTRM has a cradle-to-grave carbon footprint of 2.7 kgCO2e. Comparatively, the carbon footprint of concrete-based alternatives are up to 10 times higher, and rock riprap is up to 30 times higher.  

Transportation requirements are a main factor contributing to the difference in carbon footprint. By making a few assumptions, we can determine how much rock riprap and concrete would be required for a project with a coverage area of 20,000 SY, and the logistics involved in transporting those materials. We can then compare the shipping miles needed to supply the HPTRM to the miles needed to supply rock riprap and concrete. The comparison and assumptions made for the comparison can be found in

Table 1.

 

While rock is a natural material, the strip mining and crushing it for use in engineering projects is often done without regard for environmental impact.  ARMORMAX is manufactured in a facility that is ISO 14001 certified.  This international certification recognizes companies that are actively measuring environmental impact and continuously looking for way to reduce their carbon footprint.

 

Vegetation and Water Quality Improvement

Sediment from soil erosion is among the top pollutants found in waterways of the United States. Erosion can occur naturally, but it’s often caused by construction and land-development activities. Other pollutants such as heavy metals and nutrients are introduced into channels and streams via runoff water, which then transports the pollutants to large bodies of water such as oceans and lakes. This polluted water can affect the well-being of wildlife that drink the water as well as aquatic life that inhabit the waterways. According to the Environmental Protection Agency (EPA), the presence of vegetation in channels and streams acts to slow water velocities, increasing filtration of heavy metals as well as encouraging groundwater infiltration.

ARMORMAX is engineered with a patented tri-lobal design that locks seeds and soil in place to promote rapid root development and provide long-term reinforced vegetation. This helps to decrease sedimentation and pollutants and encourages infiltration of water back into the ground water table. systems that utilize HPTRMs as a Best Management Practice (BMP) for improving water quality.  Conversely, rock does not promote vegetation and offers poor filtering and pollutant remove capabilities.

Vegetated outcomes also support a living shoreline, whereas hard armoring can decrease streamside vegetation and adversely impact fish populations.  A vegetated shoreline helps to maintain cooler water temperatures, while traditional hard armoring can perpetuate thermal pollution.  This factor is important for projects in environmentally sensitive locations.

Environmentally Sensitive Applications

Murrieta Creek is an example of an environmentally sensitive project where the USACE successfully installed ARMORMAX to stabilize the channel banks. The creek, which traverses the cities of Temecula and Murrieta, California in a densely populated area, has a history of devastating flooding and environmental impacts.  More than 600 homes and commercial structures, the nearby Pendleton Marine Corps Base, and local infrastructure such as roads and sewage treatment facilities were vulnerable to flood damage. The purpose of this project was to prevent such flooding by conveying the 100-year design flow within Murrieta Creek.

In additional to maintaining the water quality of Murrieta Creek, preserving the natural habitat and minimizing impact on wildlife was also a main concern.  This section of Murrieta Creek is home to 500 plants and more than 300 bird, mammal, reptile and fish species.  The U.S. Fish and Wildlife Service and EPA, have stipulated that Murrieta Creek is one of the last high quality minimally disturbed riverine environments in Southern California.

Older Turf Reinforcement Mat (TRM) technologies have been problematic for entrapment of smaller animals and reptiles. These technologies use a stitch-bonded with netting configurations that creates larger opening sizes in the material that typically ranges between 0.2 – 0.39 in2.  ARMORMAX uses a woven configuration with a tight, three-dimensional matrix that produces openings smaller than 5mm2.  In areas with a sensitivity to wildlife, a very small opening size of < 5 mm2 (0.01 in2) is recommended to decrease the likelihood of the entrapment.  Additionally, woven HPTRMS have a higher tensile strength than stitch-bonded TRMS, making it much more resistant to damage from animals and construction traffic.

After ARMORMAX was installed along the channel slopes, vegetation quickly established providing a solution that that supports the riparian habitat surrounding Murrieta Creek. Today the reinforced slopes remain free from erosion and ecosystem is thriving. 

 

Innovations for Green Infrastructure

Commonly, green solutions cost more than traditional options; however, the average installed cost of rock riprap is more than twice the installed cost of ARMORMAX.  Plus, ARMORMAX has a design life of up to 75 years with little to no maintenance, reducing the cost of upkeep and replacement.

Propex has continued to build on the success of ARMORMAX, designing systems for a range of flood mitigation applications.  SCOURLOK®, an engineered bank stabilization system is one new technology designed to resist hydraulic stresses and protect shorelines from scour forces while promoting vegetation. It was developed for applications that need scour protection underwater in addition to slope stabilization and erosion control above water, but has also been successfully used to stabilize roadside shoulders.

The system’s design features rigid and interlocking cells armored with superior erosion control protection utilizing PYRAMAT® 75 HPTRM and the separation capabilities of GEOTEX® nonwoven geotextile. Each cell assembly can be articulated to accommodate a variety landscapes.  

PYRAWALL® is another innovative technology for resilient flood mitigation.  The system combines a robust HPTRM with fiber-composite internal bracing to create a vegetated solution for constructing reinforced soil walls.

Like ARMORMAX, both SCOURLOK and PYRAWALL offer long-term performance that is more environmentally friendly and more cost effective than traditional hard armoring solutions.

To learn more about our environmentally friendly flood mitigation solutions or read full case studies on any of the mentioned projects, visit www.PropexGlobal.com or contact Propex GeoSolutions Engineering Services Team at 423-553-2465 or email GeoEngineering@propexglobal.com