GB2299920A

GB2299920A - Floating fish pass

Info

Publication number: GB2299920A
Application number: GB9508381A
Authority: GB
Inventors: George Baillie
Original assignee: WATER POWER DEV Ltd
Current assignee: WATER POWER DEV Ltd
Priority date: 1995-04-20
Filing date: 1995-04-20
Publication date: 1996-10-23
Also published as: GB9508381D0

Abstract

A floating fish pass pivots at the downstream end and buoyancy devices maintain the entrance to the pass at a fixed depth below the water level. The pass included removable wooden baffles mounted in the rectangular channel of the pass. The pass allows the free movement of fish while losing only the necessary amount of water for the movement of the fish.

Description

FLOATING FISH PASS This patent application relates to a floating fish pass.

Fish passes are constructed in rivers where man made structures impede the progress of migrating fish to their spawning grounds. The passes are designed in such a way that the velocity of the water in the channel does not exceed the swimming capacity of the fish, there is sufficient physical and visual clearance to accommodate the expected size of fish, and to have sufficient flow and a well located entrance to attract the fish.

Previous fish pass designs for large dams use fixed structures which will allow flows in the pass to vary with changes in reservoir water levels. When considering a small hydroelectric scheme, where size of the dam or weir is much smaller, it is important that the loss of water through a fish pass is kept to a minimum, within design guidelines for required depths of flow for fish movement, at all reservoir levels to maximise the reservoir storage available for electricity generation.

In this design for a fish pass, the structure pivots at the downstream end located at or below the existing river bed level. The entrance level of the pass will be maintained at the required depth below the reservoir water level using floats allowing the necessary flow through the pass.

The pass consists of a rectangular section channel with V shaped baffles closely spaced along its length and set at an angle to the axis of the channel. The energy of the water is dissipated by the transfer of momentum to the flow in the open sections of the pass from the relatively narrow baffles. This causes a greater depth of water at low flows and velocities within the capabilities of the fish.

Enclosed with this application is the proposed design of the pass : The Baffle Section shows the dimension of the channel constriction (proportions as recommended in Ministry of Agriculture, Fisheries and Food Fisheries Research Technical Report No. 78, ISSN 0308-5589 (1984)).

The Longinedinal Section illustrates the location of the fish pass relative to the weir, the angle and spacing of the baffles and the reservoir water level.

Sect'on A-A is taken through the upstream end of the pass and shows the floating devices and vertical restraints to ensure that the pass does not move horizontally.

The length of the pass is dependent on the maximum difference in water level between the reservoir and the river to ensure that the maximum gradient for this type of pass of 1:5 is not exceeded.

Due to the location of the fish pass in the reservoir, when the water level is at a maximum, the structure will need to be weighted to compensate for the water pressure causing upwards force. The self weight of the structure will be sufficient for this purpose. The floats will not have any buoyant effect being located at the water level as the water level drops but will maintain the level of the structure as the pressure reduces. As the water level rises from the minimum level the buoyancy will cause the structure to rise. The amount of buoyancy must therefore be sufficient to lift the self weight of the structure and the amount of water contained in it.

To avoid injuring the migrating fish as they use the pass, the surface of the baffles must be smooth and edges rounded. For this reason the baffles will be made of wood and connected to the channel in such a way that they can be removed and replaced easily should damage occur.

Claims

1 A floating fish pass comprising of a rectangular channel, removable wooden baffles, buoyant devices, vertical supports founded on river bed, maintenance free pivot bearings and flexible rubber membranes.

2 A floating fish pass as claimed in Claim 1 whereby the structure is free to raise and lower about the pivot point.

3 A floating fish pass as claimed in any preceding claim where the pivot is created using maintenance free bearings allowing vertical rotation

4 A floating fish pass as claimed in any preceding claim wherein floats ensure the fish entrance/exit bell mouth is maintained at a fixed level below the reservoir water level to provide a sufficient flow of water for fish to travel.

5 A floating fish pass as claimed in any preceding claim wherein bed founded columns provide lateral support while allowing free vertical movement of the structure.

6 A floating fish pass as claimed in any preceding claim wherein fish pools are created with wooden baffles placed at equal centres in the channel.

7 A floating fish pass as claimed in any proceeding claim wherein all exposed faces are smooth and edges rounded to avoid injury to fish.

8 A floating fish pass as claimed in any previous claim wherein rubber meinbranes located between the weir and the fish pass to ensure water is not lost other than through the pass.

9 A floating fish pass substantially as described herein with reference to the accompanying drawings.