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Erosion Control and Stormwater Management with ACBs

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Articulating concrete block provide an aesthetically pleasing solution to manage stormwater runoff.

CEU Learning Objectives Stormwater Management: At the end of this article, participants will be able to:

  • Describe articulating concrete block and articulating concrete block mat systems and components
  • Understand erosion at water fronts and river embankments caused by stormwater runoff and the role of ACBs in mitigating that erosion and preventing overtopping of adjacent water bodies.
  • Explain how unchecked stormwater runoff affects downstream water bodies. o Describe how ACB pavement systems can control erosion on site and maintain the integrity of the site’s environment.

With urban areas expanding, the severity of heavy rainfalls increasing, changing climates causing flooding and polluting waterways, erosion control of stormwater is a pressing concern. Runoff from heavy rains can cause severe erosion, site disruption and infrastructure damage, and also threaten the environment.

Stormwater comes from precipitation events, which most often are rainstorms but also include melting snow that makes its way into stormwater systems. Some stormwater seeps into the ground, although heavy rains in urban locales with large impervious areas such as roads, sidewalks, driveways, parking areas, building roofs, and even some lawns, are most likely to generate surface runoff. Heavy rains cause the runoff to move at a high speed and lead to erosion on building sites, along streams and river banks, and at shore lines. In addition to the physical damage inflicted by rapidly flowing stormwater, that runoff can send significant volumes of unfiltered water and pollutants picked up along the way to sewers, which discharge into and contaminate streams, lakes, and distant waterways.

The two main issues surrounding stormwater are seemingly not complex: the volume of rainwater falling and the velocity of the runoff. But as impervious surface area increases, there is less ground area available to absorb the rainwater. Less infiltration and less absorption in turn can lead to unanticipated surface erosion in natural sites as well as where landscape is maintained, along with flooding, both on the site and downstream, and also transport of soil sediments and surface pollutants to vital waterways.

Left unchecked, stormwater runoff can cause widespread erosion damage to the areas around water bodies and to communities and watersheds. As a result, local, state, and federal governments are stepping in with recommended best management practices, standards, and regulations to counter the problem. The industry is responding with innovative products, systems, and designs.

Controlling source water

One such system is a matrix of articulating concrete block (ACB), a system used for erosion control that can also be used as an interlocking pavement comprised of individual concrete blocks. When set together individual ACBs create an armor system above a stream bank or shoreline. The system is comprised of the concrete block cover layer—the armor, one or more filter sublayers, and the soil base below. The individual units offer the density, durability, strength, and impact resistance of a concrete block while at the same time providing a matrix that is flexible and allows infiltraton. For a detailed discussion of ACBs and Erosion Control, see NCMA TEK 11-09B.

The system is “articulating” because individual blocks can shift slightly, without unlocking from the matrix, and conform to changes in the subgrade. There are a number of ACB configurations and they all vary in plan, cross section, and locking mechanisms. Each of these proprietary systems offers flexibility of movement, yet is restrained by virtue of the individual block geometry, along with additional system components such as cables, or geotextile ropes. The physical interlocking feature provided by the special shapes of ACBs also allows for expansion and contraction.

Flexible ACB revetment systems are effective because they will conform to variations in subgrade soils, and as a result, subsoils should be carefully prepared. However, subsoil shifting is still possible, and so the ability of these revetments to also shift, yet still maintain contact with the filter and base, is what makes them so successful.

Waterfront areas offer recreational and commercial opportunities and access to natural environments. They also offer the potential for erosion, flooding and storm damage, and can require manmade protection to shield fragile environments, ensure personal safety, and preserve property. ACB revetments are an ideal solution under heavy water flow conditions, flash flooding and where high velocities of runoff water are expected. The individual block nature of these systems makes installation around trees possible and also around and above infrastructure such as storm drains and water pipes.

Articulating concrete blocks perform double duty as flexible revetment systems that provide effective erosion control at riverbanks and shorelines and can also incorporate plants to maintain a natural appearance, further assisting in erosion environmental benefits of permeable pavements.

One environmental benefit of ACB erosion-prevention matrices is the inclusion of vertical cores and spaces in the systems, which allow plants to grow and water to infiltrate. Properly selected plant species can be installed across the hard surface of the ACBs, to blend in with the site features and help with water purification by absorbing nutrients and breaking down other pollutants.

The overtopping at Lake LaMoure in North Dakota was undermining the water body, leading to the destruction of the soil and causing severe erosion to the lake banks and surrounding areas (see Erosion Control at Lake LaMoure Spillway). But, a massive ACB installation was able to solve that problem and control flooding. The system installed over a drainage layer maintains the inherent drainage and treatment systems of the soil, reducing water runoff and flooding risks, improving water quality, reducing pollutants, recharging aquifers, and preventing erosion. With plant matter included, ACBs can also contribute to habitat. All of these characteristics make an ACB system a great candidate for use in sustainable projects where stormwater management is of concern and erosion control is a priority.

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