A fish ladder is also known as a fishway, fish pass, or fish steps is a structure on or around artificial and natural barriers (such as dams, locks, and waterfalls) to facilitate diadromous fishes the natural migration as well as movements of potamodromous species.
Generally, it is provided beside the baffle wall for the movement of fish whereas rivers are an essential source for fish and there are numerous varieties of fish within the river.
The nature of the fish varies by its types and the fish tend to move upstream in winter and upstream to downstream in monsoon, this movement is necessary for their survival.
Due to the construction of a weir or barrage, this movement is disrupted and it is harmful for fishes.
A fish ladders are necessary for the movement of fish along the way of the river, while baffle walls are constructed in a zigzag manner so that the movement velocity throughout the ladder doesn’t exceed 3 m / s.
The width, size and height of the fish ladders depend on the character of the river and the kind of weir or barrage.
Properties of Fish Ladder:
- It is usually located between the wall of the weir and the divider.
- This is favorable near the wall of the divider because there is always some water in the river section.
- It consists of an inclined trough with holes, with holes in it.
- For effective control, grooves gates are provided on the top and bottom walls.
- This fish ladders must have a velocity of 3 m / s or less in the trough.
Types of Fish Ladder:
1.Pool and Weir Fish Ladder:
This fish ladder is an extensively fish movement structure consisting of a sequence of small overflow writs and pools of normal size.
In this case, the fish need to leap from one pool to a different to migrate upward.
Pool and weir fish ladders are suitable for all types of structures, either small scale or large scale, however, they require a large space construction.
2.Pool and Orifice Fish Ladder:
This fish ladder is almost similar to pool and wear fish ladders and the only difference is the overflowed wear provided with a submerged hole inside its body.
Therefore, the fish can travel upwards passing through each hole instead of just jumping upwards.
3.Vertical Slot Fish Ladder:
This fish ladders is a ladder pool and another variety of weir fish.
In this case, the walls are replaced with vertical slots so that the fish can simply move through these slots from pool to pool and upstream.
In some cases, multiple vertical slots are also provided.
4.Baffle Fish ladder:
This fish ladder is in the form of a rectangular channel with a series of seeds still emerging in the same direction.
Typically, in the ease of dodging fishing, water flows continuously without resting unlike a pool-type fish ladders but still, pools can be provided between the baffle walls if necessary.
Denil Fish ladders are classic baffle fish ladders, where baffles are provided on the sides and floor of rectangular pass whereas in the ease of the Larinier Fish ladders and the Chevron Fish ladders baffles are provided on the nearby floor.
Alaskan Fish ladders are recommended for steeper slopes.
5.Rock ramp Fish ladder:
This fish ladder is built using large size rucks and wooden logs.
This fish ladders are rock ramp is prepared directly over the barrier in its width with some slope.
Pools and tails are made by these massive rocks in such a way that the fish can simply cross over them.
Fish elevators also called as fish lift is another type of fish in which the fish is lifted from the bottom to the top by a chamber filled with water.
The Fish lifts are well suited for long barriers such as arch dam, high weir, etc.
In this type, fish passes through fish elevator in larger quantities over a given time.
Some larger sized species cannot travel upstream nearby due to smaller size openings, poor swimming capabilities.
7.Siphon Fish ladder:
The fish siphon or siphon fish ladders are closed fish pass that is provided between two watercourses.
The fish enters the siphon tube which is partially filled with water and the flow rate in this tube is controlled by the siphon effect.
This fish siphon allows all kinds of species through it and is kept with small gradients, it is best suited for the migration of fish during the flood period.
Also read: Weep Holes, River Training Works & Curb and Gutter
Fish ladder is actually an artificial passage designed for fishes, which allows them to remove obstruction or barrier in their journey.