Highway 8 Hydrotechnical Emergency Response

Project Highlights

In just two days, the November 2021 atmospheric river dropped months’ worth of rain across southern British Columbia, causing widespread flooding and damaging critical infrastructure, including Highway 8. Highway 8 traverses the adjacent Nicola River and provides vital access to several communities between Merritt and Spences Bridge.  There were 25 damaged sites, with 7km+ of highway lost and 60km+ of river channel devastated.  Communities lost access to their homes, electricity service, and emergency services.  In addition, a few secondary roads connecting the Highway 8 corridor were not accessible by heavy construction traffic, requiring construction to progress linearly through the corridor.

The Nicola River experienced a record flood, estimated at 750 m³/s, almost double the previous flood.  The lateral migration of the river channel and bank erosion changed the river alignment.  They exposed Highway 8 to increased slope stability issues, rockfall and landslide hazards (geohazards), and river-related hazards (hydrotechnical).  Where possible, MoTI reinstated the highway along the pre-flood highway alignment.  However, this was only sometimes feasible due to pre-existing geohazards caused by forest fires exacerbated by the flood.  The flood also devastated fish habitats and riparian vegetation throughout the river system.

The highway was rapidly reconstructed using the non-traditional approach of Construct-Design-Construct-Plan (CDCP).  In addition, KWL developed a typical cross-section for the corridor based on previous KWL knowledge of the Nicola River valley, intending to have erosion protection in the ultimate location, minimizing future instream works in the recovery phase.  With this approach, KWL eliminated design delays as subsequent isolated sites were accessed.

Restoring connectivity to the cut-off communities required immediate reconstruction of the highway.  A balance between public safety and nature was essential with the existing and new flood-induced hazards.  The highway needed to be pushed further into the newly defined river channel to a safe offset distance to avoid geohazards.  Still, river encroachment needed to be minimal to maintain river capacity and fish habitat.

Crews began construction immediately, starting at both ends of the damaged highway.  KWL developed a cross-section template, utilized available riprap gradations, minimized encroachment into the river, and protected the public from geohazards.  As the updated design parameters were unavailable at the time, the design had to allow flexibility for raising the road without additional instream works and for implementing other erosion protection measures (e.g. groynes, spurs, etc.) if required in the future.  The design cross-section was refined as work progressed through the corridor, and new sites were accessed.  In addition, habitat enhancement features of live willow staking, boulder clusters, and habitat groynes were installed at select locations to initiate habitat recovery.

Highway 8 was reopened to the public 360 days after the catastrophic flood.  The 25 repaired sections of the highway are now more resilient to future floods through the placement of riprap, road fills of less erodible materials and incorporation of geohazard experience.  The CDCP approach allowed the response works to be initiated and completed before identifying and accepting updated design parameters.  This resulted in the faster reconnection of communities and getting families back into their homes.