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Culverts: critical freshwater infrastructure

British Columbia is a province of natural abundance. One of our sometimes-overlooked bounties is clean fresh water. Home to nearly 300,000 kilometres of streams and rivers, over 20,000 freshwater lakes, and thousands of glaciers, BC’s abundant water resources enable large-scale hydroelectric power generation and extensive farming that helps feed Canada and the world at large.

Protecting our precious water resources is paramount to the continued environmental, social, and economic stability of our province. One overlooked way to protect our waterways is through sustainable infrastructure management.

Culverts are structures used to channel water through obstacles like roads. There are many types and sizes of culverts, ranging from small diameter plastic piping beneath a residential driveway to massive concrete or steel channels under highways.

Culverts may be used for drainage to avoid pooling and flooding along roads and highways, or to allow natural streams to flow beneath roads unimpeded.

Like all infrastructure, culverts have a lifespan, requiring replacement or repair after anywhere from 20 to 100 years. The precise mechanism of failure varies by culvert type, but may include factors such as:

• Rust, corrosion, and physical damage to the culvert causing structural integrity loss
• Formation of blockages due to debris accumulation
• Changes in water flow necessitating a different culvert size or type
• Erosion of surrounding bedding and backfill
• Seasonal freeze-thaw cycles warping or damaging the culvert
• Vandalism/human interference with the culvert

Extreme weather events like the historic 2021 floods can result in widespread damage to culverts and drainage systems, necessitating widespread repair and replacement.

The ecological cost of conventional culvert replacement

Conventional construction methods for culvert replacement can result in a number of undesirable environmental outcomes.

When compared to trenchless solutions, a conventional replacement process is a blunt instrument. Conventional culvert replacement involves complete excavation of the existing culvert, a process that can take days or even weeks.

During this process, road closures are necessary. Disruptions to road traffic can result in higher vehicle emissions due to detours or delays, not to mention a loss in human capital caused by longer commute times.

Disrupting a large volume of soil through excavation poses a number of ecological concerns. Excavation is a carbon-intensive process that can contaminate waterways. Disrupting the soil around a culvert can damage local habitats and even change the flow pattern of the stream, potentially impacting fish and other wildlife.

During excavation, the stream’s flow may be significantly disrupted, which can impact fish—particularly during spawning season. Heavy equipment poses risks to water quality, as fuel and oil leaks can contaminate the site.

Trenchless solutions for culvert repair

Trenchless technology enables a less disruptive method for culvert repair and replacement. A typical trenchless culvert replacement requires little or no excavation, greatly reducing contamination and damage to the surrounding site. Nearly any type of culvert may be remediated or replaced with trenchless technology through one of several applicable methods.

Trenchless technology is proven to be a less carbon intensive method for construction. Its reduced excavation requirements mean far less disruption for drivers while better protecting vulnerable ecosystems from harm.

Trenchless culvert replacement techniques

CIPP (Cured-in-place-pipe)

Cured-in-place pipe is an ideal solution for small to mid-sized diameter culverts. CIPP uses the existing run of the culvert, inserting a length of resin-saturated felt lining into the pipe. Using UV light, heat, or a combination of both, operators cure the resin in the felt lining, producing a durable new culvert without requiring any excavation.

This is an ideal solution for leaky culverts. The process does result in a narrower culvert than the original, so this technique is not suited to high flow rate applications where sacrificing pipe diameter is unacceptable.

Slip lining

Somewhat similar to CIPP, slip lining involves inserting a new pipe within the existing run of the culvert. Once the pipe is in place, it’s grouted or cemented to ensure stability. Like CIPP, the diameter of the culvert will be reduced, making this technique unsuitable to certain situations.

Pipe bursting

If maintaining culvert inside diameter is crucial, pipe bursting may be a good solution. Using a variety of mechanical methods, the existing pipe is destroyed as a new pipe gets pulled through the cavity of the previous culvert. This technique can be used to maintain or expand the diameter of a culvert, and is suited for scenarios where the culvert is severely damaged or even collapsed.

Panel lining

Not all culverts are simple pipes. Many culverts are concrete or metal tunnels more akin to a bridge than a pipe. In these cases, trenchless repair may involve panel lining. Durable panels get installed and secured to the inside of the existing culvert. Steps are taken to reinforce the panels, ensuring durability and effectiveness for decades to come. This carries the same risk of reducing the inner dimensions of the culvert, affecting flow rate accordingly.

Scenario: fish-friendly rural culvert replacement

Let’s explore a possible scenario where trenchless technology might be employed for a culvert replacement.

Imagine a rural road with a culvert running beneath it. The stream flowing through the culvert is an important route for spawning rainbow trout.

The culvert is in dire need of repair. Decades of exposure to the elements have eroded the corrugated metal pipe, threatening the structural integrity of the culvert and risking an eventual cave-in that would damage the road and block the stream.

PW Trenchless is often engaged and provides advice on potential solutions to rehabilitate culvert while minimizing impact to local fish populations.

Before beginning any construction work, a proper assessment of required permitting and all environmental constraints is necessary. In addition, hydrological analysis of the site helps inform the ideal process for replacement. Engagement with local stakeholders such as environmental groups and indigenous communities informs an action plan that suits the needs of the community.

After evaluating the scenario and understanding the constraints and requirements, slip lining is deemed to be the best method for replacement. The stream’s flow is deemed low enough that reducing the interior dimensions of the culvert will not cause issues.

With the project awarded, PW Trenchless proceed with sourcing suitable liner pipe and confirmation that appropriate permitting is obtained for this sensitive environment works. They perform a typical slip liner installation process over the span of two weeks, including site preparation, diversion, pipe inspection, cleaning, installing the liner and filling the annular space.

Once the new pipe is installed, flows are reinstated and site remediation is completed, returning the area to its natural state.

A post-installation inspection is conducted to ensure compliance and satisfactory completion, ensuring no issues occur for the future performance of the culvert.

Conclusion: trenchless technology enables sustainable water management practices

From carbon emissions to habitat protection, trenchless technology marks an improvement over conventional replacement methods for culverts. Whether it’s reducing traffic impact when working in urban environments or protecting sensitive spawning grounds in rural areas, consider the benefits of trenchless technology for your next culvert replacement.

Do you have questions about trenchless culvert management? Get in touch with our sales and estimation team today to request an estimate!