Flexi Baffle Installation at Bon Accord Creek – Surrey, BC

In August 2023, an innovative and ground-breaking restoration project was completed within Bon Accord Creek in the City of Surrey (City) to restore historic fish passage through a segment of channel where a concrete flume structure had been installed. The project represents a significant achievement in local fish habitat restoration, being the largest Flexi Baffle installation project in North America, with 62 flexi baffles installed along the creek’s 150 m concrete flume structure.

Flexi Baffles are a flexible polymer rubber baffle or weir used to improve fish passage and connectivity through water flow modification and regulation. Completion of this innovative fish habitat restoration project successfully resulted in the return of Coho salmon to the upper reaches of Bon Accord Creek, a tributary to the Fraser River, for the first time in over 70 years!

Collaboration was key to the success of the project and represented a partnership between the City of Surrey, Resilient Waters, Watershed Watch Society, Surrey’s Salmon Habitat Restoration Program (SHaRP), Dillon Consulting Limited, and the local landowner. Installation of the baffles was zompleted by SHaRP, a City program managed by Dillon from SSA Environmental. SHaRP employs local university and high school students in completing fish habitat restoration and environmental education. SHaRP’s involvement in the project served as an integral career building opportunity, providing hands-on experience in environmental management and community stewardship.

History of Bon Accord Creek

Bon Accord Creek, a small creek located in north Surrey once provided spawning and rearing habitat to anadromous salmon species. In the 1950s, land development resulted in a railyard adjacent to the Fraser River and the creek was relocated from its original alignment and channelized into the present-day concrete flume. When the creek was redirected through the flume, a section became impassable for salmon to move upstream, resulting in the loss of access to approximately 2.5 km of critical upstream spawning and rearing habitat.

In 2017, the City began restoration of Bon Accord Creek through the removal of a historic timber dam structure and a large culvert that impacted fish habitat quality and passage. In 2023, Dillon used eDNA sampling to confirm the concrete flume within Bon Accord acted as a barrier to passage for Coho salmon. Sampling confirmed Coho presence below the concrete flume and none upstream. The findings solidified that the remaining piece to restore fish passage within Bon Accord was the modification of the flow conditions within the flume structure to support fish passage requirements.

Innovative Solution to Fish Habitat Restoration

Fish barriers across the Lower Mainland, such as hanging culverts, floodgates, and dams, prevent fish from accessing well-needed spawning and overwintering areas. In the City of Surrey, and other municipalities, efforts to improve fish passage are often impeded by the cost of instream works (e.g., construction design and implementation costs), permitting process limitations (i.e., requirement for Water Sustainability Act Approvals), and access constraints (e.g., steep ravines, private property). These impediments were present at Bon Accord Creek when considering fish habitat restoration options. Should the concrete flume have been removed in its entirety, established understory vegetation and trees, and the risk of future flooding, would have caused significant disturbance to the area.

Given these challenges across the Lower Mainland, and at Bon Accord Creek in particular, solutions to improve fish passage needed to be quick and easy to implement, cost effective, low risk, and effective. These factors are why the potential use of Flexi Baffles sparked the City’s interest – a new, efficient, economical, and proven solution to improve fish passage. The Flexi Baffle, developed by ATS Environmental in New Zealand and supplied by North American distributor SSA Environmental, is a flexible polymer rubber weir that is bolted to a channel bottom to modify and regulate flow through a structure. The design reduces the need for “hard” solutions (e.g., solid weirs), which can often affect the hydraulic capacity of a culvert or capture debris which can increase flooding risk. Given the flexible nature of the Flexi Baffle, it allows for water and debris to bend the baffle and pass over it during higher flow events, preventing build up from damaging a structure. In shallower water conditions, the baffle returns to a vertical position and supports the pooling of water, increasing water depth, and slowing water velocity to improve fish passage potential. The goal of Flexi Baffle installation at Bon Accord was to use a “fish friendly solution” to improve water flow within the concrete flume and create more desirable conditions for fish to migrate upstream to their historical and rearing spawning area, while also protecting the established ravine slopes and surrounding riparian vegetation.

The ease of installation associated with Flexi Baffle technology meant it was a perfect fit for the SHaRP team to complete in August 2023. SHaRP members installed 62 Flexi Baffles along the 150 m Bon Accord Creek flume, with the guidance and training of Dillon and support from SSA Environmental. Eighteen SHaRP students participated in the installation, many of which expressed this project was their favourite of the season – a testimony to the success of fish habitat restoration and education of restoration methods!

Success! Coho Salmon Return!

In the fall of 2023, approximately three months after the Flexi Baffles were installed, Coho salmon were observed within the flume of Bon Accord Creek, moving upstream to areas they have not inhabited in over 70 years! The Flexi Baffles installed by SHaRP successfully reduced the water velocity of the creek and increased dry weather water depth, creating favourable conditions for fish movement. Flow conditions created by the baffles also allowed for important fish habitat features to develop. Where once the flume invert was bare of any gravel substrate there is now development of more naturalized features at each baffle location as observed by the aggregation of gravel, fines, and small woody debris. These features also protect the concrete structure from scour and provide habitat for benthic macroinvertebrates.

The City’s trailblazing application of Flexi Baffles at Bon Accord Creek represents the successful implementation of a newer innovative technology in North America and provides a prime demonstration site to other municipalities struggling with similar infrastructure challenges. The City, SHaRP, and Dillon are exploring installation at six sites in 2024. This technology is transferable to many other sites across the Lower Mainland to restore habitat for important tributaries to the Fraser River, one of the most prolific salmon rivers in the world. The restoration of Bon Accord Creek is just a first step! This project shows how the collaboration of a wide range of Lower Mainland partners can lead to the successful restoration of salmon habitat using creative, effective, and efficient methods that can easily be applied to problematic structures across the region. As the largest Flexi Baffle restoration project in North America, the accomplishments of this project are far-reaching in the application of new and innovative technologies to solve long-standing fish habitat restoration challenges.

Awards

• Environmental Managers Association of British Columbia, Technical Innovation Award, 2024

Project Details

Project Partner: City of Surrey
Business Unit: Environmental Management
Service Offering: Environmental Compliance and Risk