Upstream Fish Passage Design
As mentioned under Fish Passage Feasibility Studies, there are numerous options for designing upstream fish passage solutions depending upon individual site requirements and the species of fish. These options may include: Baffle-Type, Vertical Slot, Pool-and-Weir, Fish Lift or Elevator, Nature-Like, Trap/Truck or Dam Modification. Our Fish Passage Design Team has extensive experience with all of the fishways mentioned.
In North America, the typical fishways that can be found at hydroelectric and other dam sites include the following:
The Denil is a Baffle-Type Fishway that was developed in the early 1900s in Belgium. Its design consists mainly of a canal with a slope in the range of 1:5 to 1:10, in which baffles are installed at a 45° angle with the bottom slope of the canal. The use of baffles allows for excellent energy dissipation and thus reduces energy requirements for fish to migrate through the system.
The Alaska Steeppass is also a Baffle-Type Fishway that was designed to be constructed out of aluminium sheets, so that it can be prefabricated and transported into remote sites.
The Vertical Slot fishway is composed of a canal in which baffles are placed with single or double vertical slots. This type of fishway is commonly used where high variations in water levels are observed. One of the advantage of the vertical slot design is that ascent of the fishway is possible at any depth the fish chooses. There can be considerable variation on depth selection by fish, depending on the fish species, time of day, light conditions, turbidity of the water, etc.
The pool and weir fishway consists of, a canal into which vertical baffles are installed, similar to a vertical slot fishway. However, these baffles act as weirs and thus control the hydraulic conditions within each pool. The pool and weir fishway is more sensitive to water level fluctuations than the Denil or vertical slot fishways.
The use of orifices in the baffles is frequently seen in this design. Such orifices allow for passage of certain fish species that show less swimming and jumping capacity than salmonids. The presence of an orifice (usually at the bottom of the baffles) allows fish to migrate from one pool to another without having to jump.
Fish Elevators are used to pass fish over high-head dams where the length of conventional fishways would result in excessive stress on the fish or excessive cost to construct. Fish elevators may also be considered for medium-head dams when considering fish species such as sturgeon and shad that have difficulties in conventional fishways. In a fish elevator attraction flow is used to draw fish into a holding chamber where they are lifted with a hopper directly to the headpond level. The main advantages of such systems are initial costs which are somewhat independent of the height of the dams, and tolerance to upstream water levels.
An alternative to the other conventional technical fishways is to put in place an artificial nature-like channel. These channels provide an environmentally friendly design that allows not only for fish passage (both upstream and downstream), it also creates fish habitat. However, their low gradient from less than 2% to a maximum of 5% to surmount a given dam height means that they will be very long compared to other systems. Additionally, nature-like channels require more space than other fish passage designs, so they would not be appropriate if space is limited, unless an in-channel configuration is possible.
A rock ramp is another type of nature-like fishway that can be installed within the extents of the existing stream channel. Instead of going around the barrier with a bypass channel a rock ramp can be constructed to allow fish to pass directly over the barrier. Rock ramps also typically have a gradient of 2-5%.
A modification to the Fish Elevator is the trapping system where instead of lifting the fish with a hopper to the headpond elevation, fish are moved from the hopper into a truck and then transported upstream to a release point. This system is used fairly frequently on rivers that have multiple barriers, especially if the upstream barriers do not yet have means to allow fish passage. Trap and truck systems give river managers flexibility for optimal distribution of the fishery resource on the river reach.
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