Featured Reports - Fishways

Background

Migration is integral to the lifecycles of salmonoids. Most people think of spawning but all stages in the life of a salmon are marked by migration:

• Alevin - swim down into gravel of redds
• Fry/Parr - seasonal movement throughout stream and off-channel habitat
• Smolt - downstream to ocean and throughout the estuarine areas
• Adult - coastal and open ocean movement
• Spawner - back to spawning redds
  
  

Impairing or preventing any of these migrations will contribute to lower survival rates for the stock and may threaten the long term survival of it.


Barriers to migration can be caused by:

• physical blockage - screens, debris, sediments
• water volume - insufficient depth
• water speed - rapids, falls, culverts
• water temperature - high or low
  
  

Fishways are structures that allow fish to overcome the barriers of blockage, volume or speed by moderating flow extremes or providing a detour that bypasses these barriers.



Assessment

Questions to ask:

• Is there a barrier to fish migration?
• What stages of life are affected?
• What is the temporal / spatial nature of the barrier?
• What would be the effects of overcoming the barrier?
  
  

To answer these questions, a survey of fish populations and habitat above and below the barrier must be conducted. The severity of the barrier is indicted by the degree of habitat underutilization. In cases of a partial barrier, the population may be skewed by species, size, age or season.

Historical records are often useful for assessing the effects of recent barriers.

The potential barrier itself can be assessed by measuring water depth, velocity and drop heights(s) over the range of possible flows. Remember that a pole with a depth at least 1.25 times the height of jump is required.

Sustained swimming speeds are the swimming velocities that can be maintained for extended periods of time. Prolonged speeds are swimming velocities that can be maintained for passage through difficult areas. Burst speeds are for escape and feeding. In addition to a species' maximum jump height, the ability to jump a vertical obstacle is also related to the depth of water from which a fish can leap.




Designs


Fishway designs should be chosen based on:

• Site geometry
• Flow conditions
• Hazards
• Species and size of fish
• Cost
• Site accessibility
• Maintenance
• Jurisdiction / regulations
  
  

Fishways can vary in size from a single pool and weir to a huge structure such as that at Hell's Gate. They can make use of baffles, slots, orifices and weirs. Construction materials include concrete, steel, aluminum and wood.



Small Stream Applications


The best design for most small streams is the pool and weir. This design will function over a wide range of flows, resist plugging with debris and can be built with relative ease from a range of materials.


The jump height varies with species and age of fish. Generally speaking, it is better to have a few jumps of maximum height than many of minimum. However, if chum and pink spawners are to use the fishway, it should be designed such that the fish do not have to jump clear but can swim up a "column" of water.


Material & Methods

Pool and weir fishways can be constructed (on-site or prefabricated) from a variety of materials.

Logs and rocks

Cost: very low
Durability: moderate
Site Access: foot (assuming sufficient materials at site)
Installation: skilled

Plywood and studs (pressure treated)

Cost: low
Durability: moderate / good
Site Access: foot
Installation: easy (if prefab)

Laminated timber (cedar or pressure treated)

Cost: low
Durability: good
Site Access: improved foot
Installation: skilled

Concrete (precast boxes)

Cost: high
Durability: good / excellent
Site Access: road
Installation: very skilled

Concrete (cast in place)

Cost: moderate / high
Durability: excellent
Site Access: improved foot
Installation: very skilled




Rules & Regulations


Any fishway work requires the appropriate approvals and licenses from MoELP and DFO. Municipalities may also have regulations governing this type of work. Consult with your community advisor.