Terri-Jane Yuzda

The Perfect Culvert

Ecologist Calls On Engineers
To Solve Fisheries Problem


Protecting the Bull Trout
Proper fish passage is essential to meet Department of Fisheries and Oceans requirements in the Foothills Natural Region, and it may take an engineered culvert to do the job.

Senior Aquatic Ecologist

As land development in Alberta continues, new transportation corridors are being built to allow access to formerly remote areas. Where access roads dissect slopes, streams are encountered and vehicle-crossing structures required.

Among other areas in Alberta, the Foothills Natural Region, which extends north from Turner Valley along the eastern edge of the Rocky Mountains, is affected by land development projects. This article focuses on access road construction in the Foothills Natural Region. It's also an appeal for ideas to help resolve a culvert dilemma, which comes out of the region's special circumstances and the warranted need to protect a sensitive fish species.

The Foothills are characterized by rolling topography. The Upper Foothills Sub-region has a mean annual precipitation of about 540 millimetres, which ranks this region among the wettest in the province.

As a result, streams that drain the slopes are small and frequent. These small streams, typically located in the headwater areas of drainage systems, often do not possess preferred fish habitat and, therefore, are unlikely to support fish.

Land developers often choose round, metal culverts to cross such streams because culverts are relatively easy to obtain and install and, therefore, are economical. In addition, culverts are assumed to be a viable option under the circumstances described since no specific regulation states they are not.

The Trouble With Culverts
Much of the Foothills Natural Region falls within the portion of the province known as the Green Area. The Public Lands Act of Alberta regulates culverts less than or equal to 1.5 metres in diameter in the Green Area. Under this legislation, these culverts may be installed without the input of a professional engineer.

The Department of Fisheries and Oceans Habitat Management Division also does not explicitly require engineered culvert designs. However, an engineered design may help satisfy DFO's policy of "no net loss of productive capacity of fish habitat" by ensuring fish passage requirements are met.

Improperly designed and installed culverts can create fish migration barriers as a result of five common conditions:

  • excess drop at culvert outlet.
  • high velocity within culvert barrel.
  • inadequate depth within culvert barrel.
  • turbulence within the culvert.
  • debris accumulation at culvert inlet.

Migration barriers may render suitable habitat inaccessible to fish. For example, the upper watershed may be unreachable by downstream fish populations or fish above the barrier may be stranded.

Enter the Bull Trout

Coincident with a large portion of the Foothills Natural Region is the range for bull trout (Salvelinus confluentus). In Alberta this species is distributed along the Continental Divide. Compared to its relatives, the bull trout has the most extensive natural range in Alberta and is considered by many to be uniquely Albertan.

Bull trout have suffered population fragmentation and decline throughout their range as a result of over harvest, displacement by introduced species, and habitat degradation. Bull trout is a "sensitive" species, which means that it is not at risk of extinction or extirpation, but it may require special attention or protection to prevent it from becoming "at risk."

For these reasons, provincial and federal resource managers intend to protect bull trout from further decline and are taking steps to ensure its population recovery. These steps may include the prevention and removal of migration barriers.

Given the risks to fish habitat associated with culverts and the status of bull trout, resource managers are hesitant to authorize the installation of new culverts in regions frequented by this species, regardless of site conditions such as stream size and habitat quality. Clear-span structures are the favoured watercourse crossing structures from an environmental point of view.

While industry generally supports the use of clear-span structures to maintain aquatic habitat quality, it is becoming increasingly concerned that an unconditional no-culverts policy is being implemented.

Clearly, concern for bull trout and other valued species is warranted. However, the requirement for clear-span structures across every hillside trickle may undermine the growing respect between land developers and regulators.

A Practical Solution?
Clearly, round, metal culverts are not the preferred crossing structure for streams with high quality habitat and the ability to support bull trout. On the other hand, culverts are the preferred crossing structure for drainages that lack fish habitat and act as conduits for surface runoff only.

Central to the culvert dilemma are streams that have little to no potential to support fish but are located in areas with sensitive environmental issues. If land developers build culverts for small streams in sensitive areas that will pass fish, even if fish presence seems highly unlikely, will regulators be more willing to approve culverts? This question remains to be answered.

Without legislation to ensure culverts equal or less than 1.5 m in diameter to be installed in the Green Area are designed by a professional engineer, it's unlikely industry will have small culvert designs stamped by an engineer. Therefore, how can fish passage be ensured and the concerns of regulators be addressed?

Can a round, metal culvert be installed using a generic design (one that does not require a site-specific design and the stamp of a professional engineer) to minimize cost and maximize fish passage potential in streams that are not likely to support fish?

While the answer may lie in the large body of literature concerned with culverts and fish passage (see Moore et al 1999), a more practical and cost-effective solution likely will be required. If you have a possible solution, please contact me at halwask@arcinc.ab.ca.

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