Rip rap is a common channel protection method because of its resistance to most flows with appropriate rock size; however, it does have significant drawbacks. Material can be expensive, not locally available, and placement requires heavy equipment. Additionally, rip rap channels are prone to regular maintenance, collection of debris and garbage, erosion at boundaries, undermining, and movement.
Naturally vegetated channels are grassed greenways that offer substantially lower maintenance and cost but are limited in their ability to resist moderate-high flows and shear forces even for short durations—unless the soils and vegetation can be stabilized.
High-Performing Vegetated Solution
The GEOWEB® Soil Confinement System offers protection to channels with continuous low flows—as well as moderate-to-high flow intermittent channels. The system’s honeycomb-like network creates check-dams that protect the soil layer from hydrological erosive forces and resulting erosion that impacts unconfined soils. Cell wall perforations lock up with the vegetative root for further stabilization.
The GEOWEB single-layer vegetated channels can withstand ~9 ft/s (2.7 m/s), more than doubling the resistance of typical unsupported vegetated channels (4 ft/s (1.2 m/s). The GEOWEB channels can withstand even higher velocities—as high as 30 ft/s (9m/s)—with an overlying Turf Reinforcement Mat (TRM) when fully vegetated. This is a significant improvement, essentially doubling performance resistance to shear stress and velocities for TRMs and Erosion Control Blankets (ECBs). Rigorous flume testing at Colorado State University (CSU) with varying shear stresses and flow rates substantiated resistance of high shear stresses up to 15.9 lbf/ft2 (77.6 kgf/m2).
Vegetated GEOWEB TRM System Compared to Rip Rap
The GEOWEB TRM System offers advantages over rip rap for vegetated channels:
- Streamlined Transition with Boundaries: Smooth integration with boundaries reduces undermining and erosion at boundary points
- Higher Permeability: Ideal for environmentally low-impact design
- Easier Integration in Landscape Plan: Less obtrusive and can be incorporated as a “soft” solution (i.e., grassed conveyances) with capabilities of some hard-armored systems
Sustainable Solution for Vegetated Conveyances
Sustainable vegetation in channels can be achieved with the GEOWEB TRM system. Applications that benefit include roadside ditches, stormwater channels, shoreline embankments, dams, spillways, and pond overflow systems. The GEOWEB/TRM system is a more sustainable—and environmentally friendly solution than rip rap for these common applications.
Presto offers full design and specification tools and a free project evaluation service to determine applicability.