Environmentally responsible stormwater pond with geosynthetics in Comox

Overview 

In Comox, British Columbia, a residential developer was required to construct a stormwater pond to support a new hillside community. The city mandated the inclusion of this infrastructure to manage runoff from the elevated development. Initially, the design called for a traditional, hard armoring solution, but the developer sought a more cost-effective and environmentally responsible alternative. Solmax was brought in to provide a solution that would meet the technical demands of the site while aligning sustainability goals and offering a more natural aesthetic. 

Challenge 

The stormwater pond was planned to be built in a former gravel pit at the base of a steep, 26% grade slope composed of highly erodible sandy soils. Stabilization of the narrow-sloped drainage channel, approximately 492 ft (150 m) long, and the dissipation pool at the entrance of the pond was critical to the design. Comox typically receives 47 in. (1,200 mm) of rain per year, and nearly 70% of it falls between the months of October and March, making it imperative to find a solution with high shear strength and flow velocity. Previous stabilization efforts were made using rock riprap, but the solution failed within two years.    

Initially, the design called for articulated concrete blocks (ACB) to stabilize the channel.  In addition to the high cost of this solution, the steep terrain and limited access made the use of heavy equipment needed to place the ACB impractical. The developer insisted on a more cost-effective and environmentally sustainable alternative. The challenge lay in delivering a robust, long-term erosion control solution that could be installed safely and effectively under these conditions.  

Solution 

First, PROPEX® Pyramattress® was selected to provide erosion control and scour protection within the channel. This engineered mattress system is designed for installations that experience constant flow of water or high hydraulic stresses. The system utilizes the durability and erosion resistance of a high-performance turf reinforcement mat (HPTRM) to construct a geosynthetic/soil/rock composite to resist scour and erosion. Approximately 9,225 ft² of PROPEX Pyramattress was installed along the bottom and side slopes of the channel. 

To provide additional protection to the slopes of the channel, 1,580 yd² of PROPEX Pyramat® 25 turf reinforcement mat (TRM) was installed. PROPEX Pyramat 25 is ideal for erosion control on moderate slopes, offering reinforcement where vegetation alone is not sufficient. This technology has been recognized by the Environmental Protection Agency as a Best Management Practice (BPM) to improve water quality.  

To ensure separation between the subgrade and the Pyramattress system, 1,120 yd² of MIRAFI® 160N nonwoven geotextile was installed. MIRAFI nonwoven geotextiles combine high water flow rates with high soil interaction and durability while providing excellent soil particle retention.  

For a secondary layer of containment, 2,800 yd² BENTOLINER® Geosynthetic Clay Liner (GCL) was installed under the Pyramattress and Pyramat 25. BENTOLINER GCL combines the dimensional stability and internal shear strength of a reinforced geotextile with the high swelling capacity and low permeability of sodium bentonite. It is commonly used as part of a barrier system in containment applications or pond closures and capping. In this application, BENTOLINER’s hydraulic conductivity and sealing effect helps contain moisture that migrates outside of the channel. 

The installation was completed manually by a crew of ten laborers, ensuring precision and safety in an area where machinery could not operate. This hands-on approach was critical given the steep slope and the fragile nature of the sandy substrate. The combination of products created a layered system that not only stabilized the slope but also improved water quality and reduced the environmental footprint of the project. 

By leveraging its diverse product offerings, Solmax was able to deliver a comprehensive solution that addressed the developer’s concerns about cost, sustainability, and long-term performance. The result was a 50% reduction in project costs compared to the original concrete design, a 90% reduction in carbon footprint, and a vegetated finish that blended seamlessly into the surrounding landscape. By replacing concrete with geosynthetics, the developer achieved significant environmental and economic benefits while delivering a resilient and visually appealing stormwater solution. The success of this installation has positioned Solmax as a trusted partner for future developments in the region.