Recovery from the 2021 Atmospheric River Event in BC provided an opportunity to rethink traditional approaches to mitigating scour and erosion of road embankments adjacent to watercourses, with a focus on integrating environmental benefits into project development life cycles. 
The Coquihalla River eroded 550m of its right bank, shifting its course 125m north and adjacent to Othello Road, leaving this section exposed to further risk of erosion.   

McElhanney Ltd and BGC Engineering Inc were retained by BC Ministry of Transportation & Transit to provide engineering and environmental design to stabilize the road embankment and improve the long-term resiliency of the road against future flooding events.  
Moving beyond traditional riprap protection, through a collaborative effort between civil, hydrotechnical, and environmental disciplines, we implemented an alternative approach involving constructing groynes that protrude into the wetted width of the river. These groynes achieve multiple design goals: 

• Redirect high-velocity flows away from the embankment, reducing quantity of riprap needed. 
  
• Create opportunities for additional and improved fish habitat.  
  
• Support revegetation with a larger footprint than traditional methods. The project planted 5,000+ native trees and shrubs over 0.4ha, delivering a net environmental gain.  
  
• Reduce the in-stream work required, facilitating regulatory authorization / approval and improving the construction schedule. 
  

Key challenges included:   

• Securing federal and provincial authorization / approval permits through early and ongoing engagement, demonstrating net environmental benefits.   
  
• An aggressive design, tender, and construction schedule, required to complete a temporary river diversion to allow construction activities within the active riverbed during the short 6-week regional window of least risk for fish and wildlife.    
  
• Selecting a soil mix that resists washout while supporting revegetation.

Our approach to stabilizing the Othello Road embankment involved innovative engineering solutions and continuous engagement of the regulatory agencies. 

A 2D hydraulic model was developed to simulate hydraulic conditions, assess mitigation concepts, and to estimate parameters for detailed design. A multiple-accounts evaluation was conducted leading to the selection of the preferred solution. This consisted of four groynes protruding approximately 25m into the Coquihalla River to deflect high-velocity river flows away from the embankment.

These groynes contribute to the creation of low velocity zones on the backside of the groynes by integrating anchored large woody debris with root wads, boulder clusters, and log jams, providing valuable rearing and potential spawning habitat for the aquatic wildlife. 

Additionally, the voids in the riprap were filled with excavated channel substrate, a structural soil and topsoil to support revegetation efforts. This innovative use of soil within the groynes enabled the establishment of vegetation, which included native planting, live staking, and seeding. The soil mix was designed to resist washout during high-flow periods, providing a stable environment for plant growth, aid in bank stabilization, and water quality for fish. 

A temporary diversion channel was used to divert the river for 500m, allowing construction activities to be completed in the dry during the limited fish timing window to minimize disruption to local wildlife.

The project, marked by its cost and time-effectiveness, environmental benefits, and use of novel techniques, not only protects the road embankment, but also supports fish habitat and the revegetation of the riverbank, offering a resilient and sustainable solution. Additionally, a more robust Othello Road, which serves as a critical transport route for residents, local businesses, and tourists, provides social and economic benefits to the region.