Controlling scour at storm water pipe outlets can be difficult based on the turbulent nature of the discharging storm water. Take into account the often odd-shaped outlet dimensions, and product selection and installation can be difficult.
Until recently, rock was used as the main source of scour control at pipe outfalls, but rock can be limiting in that it cannot offer a vegetated design and is often difficult to maintain. North American Green’s ShoreMax™ soft revetment scour protection mat was introduced recently with the intended use of providing high-performance supplemental scour protection–in conjunction with turf reinforcement mats (TRMs), geotextiles or sod–against turbulent flows and wave attacks. The mat was designed as mechanical protection over highly erosive areas, while allowing for vegetation to establish through it.
Scour Solution
A recent site installed the mat at the mouth of an 18-in. storm water drainage pipe that discharges storm water runoff from approximately 4 acres of industrial property. Under heavy rain conditions, the pipe can run at a 6- to 12-in. capacity. With loamy soils, the site experienced past scour erosion even with lightweight erosion control blankets and vegetation established at the mouth of the outlet.
The scoured area in front of the pipe outlet was regraded and seeded, and a lightweight TRM was installed. The ShoreMax™ mat was then installed over the TRM. The mat is a unique, highly flexible UV-stabilized rubber solution; it is designed with voids to allow vegetation establishment through the mat, or natural infilling of sediment. The flexible nature of the product allows for easy installation in curved channels and uneven soil beds. It also has an integrated panel interlock system that lets adjoining panels connect to form a single united mat. Unlike rock riprap, poured concrete or articulating blocks, the installation of the ShoreMax™ does not require heavy equipment or excavating soils.
In this project, the mat was installed with 12-in. pins and washer heads. Typical installations can be conducted with fasteners ranging from 8-in. wire staples to earth anchors, depending on the soil type and application. Unlike rigid transition mats made from polyethylene that specifically require earth anchors to “buckle” the mat down and force conformance with the underlying surface, ShoreMax™ mats are highly flexible and self-conforming to even minor inconsistencies in the soil. Furthermore, the mats have a specific gravity of 1.45, so they will not float or tend to uplift in submerged, turbulent conditions like polyethylene mats, which are inherently lighter than water.
The Grass Is Greener
The ShoreMax™ mat system vegetated within one month of installation, leaving a scour protection area that is an easily maintained, “green” soft armored system. Once vegetated, riding equipment can mow over the product without worry. Since its installation, the mat and the established vegetation have withstood several large storm events with no visible erosion or scour occurring.
Learn more about the ShoreMax™ approach in the brochure (PDF).
Jill Pack works for North American Green. She can be reached at jpack@nagreen.com, website www.nagreen.com.
