NZ627708B - A fish trapping and relocating system - Google Patents

Abstract

Fish, typically eels, are directed along the oblique section of screen 12 located in an obstacle, typically a dam, between two walls 5 and 6 of the obstacle to a portion of the screen that allows them to pass through larger apertures so as to enter one or more traps 11 which can be lifted out by mechanism 13 so as to be transferred to a downstream location hanism 13 so as to be transferred to a downstream location

Description

James & Wells ref: 702954/62 A FISH TRAPPING AND RELOCATING SYSTEM TECHNICAL FIELD The invention relates to a system and method of trapping fish. The invention particularly relates to trapping migratory fresh water fish in situations where there is a man-made obstruction, such as a dam.

BACKGROUND ART It is not uncommon in New Zealand and elsewhere around the world for a waterway to be partially or totally blocked by an obstacle. Man-made obstacles in waterways range from a simple weir through to a large dam. A dam is usually built to create a reservoir of water, often in the form of a lake, upstream of the dam. The reservoir may be used to store water for drinking or irrigation, for example. Many of the larger dams are part of a hydroelectric power scheme, where water from the top of the dam flows down chutes to a power station at the base of the dam. Turbines in the power station are driven by the high pressure water flow from the chute. In many rivers there can be several hydroelectric power schemes (and dams) between the source of the waterway and the ocean.

We will refer throughout this specification to an obstacle being a dam. However, this is for clarity only and it should be remembered that other forms of obstacle exist, creating similar problems to a dam.

One problem that dams create is that they provide a barrier to fish swimming upstream and/or downstream. This is a particular issue for fish that migrate for breeding or other reasons.

Until recent times the fate of such fish was not a major concern for those designing, constructing or operating a dam. However, this has changed for a couple of reasons (at least).

The first issue is practical in nature. Fish can and do get caught up in water flow over a spillway (when open) or by being sucked into an intake, often referred to as a turbine bay, through which water flows from the reservoir into the chute to the powerhouse. Some fish get caught on the penstock screen, which commonly results in severe injury or death of the fish.

Any fish that do enter the chute encounter huge pressure and turbulence and are probably dead by the time they hit the bottom of the chute. The fish bodies then end up in the turbines where what’s left of the bodies is pulverized. Over time the pulverized fish remains can build up and affect the performance of the turbines. This can lead to increased maintenance of the turbines, resulting in costly down time and/or loss of generating capacity of the power station.

James & Wells ref: 702954/62 The second issue is environmental in nature. Many people are increasingly concerned about the impact of human activities on the environment, especially how those activities affect the flora and fauna of the region. This concern is heightened when there is concern for endangered native species.

New Zealand lakes and reservoirs include fish such as eels that have grown into adults upstream of the dam. Eels, like most New Zealand indigenous freshwater fish species are diadromous and, when mature, require access to the sea to complete their life cycle.

There are dominant species of indigenous eels in New Zealand waters: the shortfin eel Anguilla australis and the longfin eel A. diefenbachii.

A recent small survey of eels found in the penstock area (i.e. in the flow channel upstream of the penstock screen through which water flows into the turbine chutes) indicated that the average age, length and weight of longfin eels and shortfin eels were: 44 years and 20 years; 1.325 m and 0.93 m; and 4.66 kg and 1.47 kg respectively. While this is only a small sample it does indicate the age and size of the eels found in the vicinity of the penstock. Importantly, these eels would have lived most of their lives (certainly since the dam was built) in the lake behind the dam and are now at a mature stage where migration to the ocean may be expected.

The fate of eels passing over the dam (via the open spillway) is either severe injury, or in the majority of cases, death.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

Throughout this specification, the word "comprise", or variations thereof such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

James & Wells ref: 702954/62 DISCLOSURE OF THE INVENTION The present invention relates to a method and apparatus designed to trap target fish upstream of an obstacle in a water flow, the obstacle being of a nature that the target fish are unable to or restricted from, navigate past the obstacle without risk of serious injury or fatality. The target fish are those fish that would in their natural habitat migrate downstream from above the obstacle to a location below. In New Zealand such fish include adult eels that have grown into adults upstream of the obstacle. Eels, like most New Zealand indigenous freshwater fish species are diadromous and require access to the sea to complete their life cycle. It is well known that eels migrate during the hours of darkness.

The water flow is typically a fresh water lake or river, and the obstacle may be a dam.

However, those skilled in the art will readily appreciate that the method and system of the present invention may be used for many types of fish and many types of obstacle, so limitation to migratory fish caught upstream of a dam should not be seen as limiting.

One feature of dams is that they commonly have an intake through which water flows from upstream of the dam over or through the dam.

According to one aspect of the present invention there is provided a method of trapping fish upstream of an obstacle, the obstacle including an intake having a first wall and a second wall, the intake being part of a flow path over or through the obstacle, the method including the steps a) placing a screen in the intake, the screen having a first portion through which the target fish can swim and a second portion through which the target fish cannot swim; b) placing a fish trap in the intake downstream of the screen, the fish trap being placed in proximity to or against the first portion of the screen, the fish trap having a fish trap entrance which is placed facing the first portion of the screen; c) allowing the target fish to swim through the first section of the screen and into the fish trap entrance; d) retaining the target fish inside the fish trap; e) removing the target fish trap from the intake; f) transporting the retained target fish to a location downstream of the obstacle; g) releasing the retained target fish at the new location.

James & Wells ref: 702954/62 The method uses a screen to guide the target fish into the fish trap entrance. The screen may allow water to flow through it so as not to create a barrier to the flow path through the intake any more than necessary.

In a preferred embodiment the screen extends from the base of the intake to at least the water surface, and across the intake from the first wall to the second wall. This is necessary to ensure that all of the target fish in the intake encounter the screen.

In a preferred embodiment the screen includes a rigid screen frame extending at least around the perimeter of the screen.

In a preferred embodiment the screen includes a screen surface which spans the entire screen frame.

In a preferred embodiment the screen surface includes a plurality of apertures. Preferably the screen surface is in the form of a mesh.

In all embodiments the apertures in the screen surface of the first portion of the screen are sufficiently large to enable the target fish to swim through.

In all embodiments the apertures in the screen surface of the second portion of the screen are too small to allow the fish to swim through the apertures.

In a preferred embodiment the second portion of the screen is inclined at an angle to the first portion.

With this arrangement the target fish may swim through the apertures in the first portion and into the fish trap entrance. The second portion, in which the apertures are too small for the target fish to swim through, is inclined with respect to the first portion to guide the target fish toward the first portion.

In a preferred embodiment a top of the frame of the screen includes a walking platform.

An advantage of including a walking platform on top of the screen is that it may aid inspection and maintenance of the screen, including removal of debris caught in the screen.

In a preferred embodiment the first portion of the screen is releasably attached to the first wall.

In a preferred embodiment the second portion of the screen is attached to the second wall.

In a preferred embodiment the attachment of the second portion of the screen to the second wall allows the screen to rotate about an axis parallel to the second side of the screen.

In a preferred embodiment the attachment of the first portion of the screen to the first wall is downstream from the attachment of the second portion of the screen to the second wall.

James & Wells ref: 702954/62 In a preferred embodiment the fish trap is placed adjacent to the first wall and the first portion of the screen.

An advantage of placing the fish trap adjacent to a wall is that it may enable an operator to access the fish trap, to lift the fish trap into and out of the water to check for any retained target fish as well as to inspect and maintain the fish trap.

In a preferred embodiment the fish trap extends from the base of the intake to at least the level of the water surface. This extension is required to ensure that the target fish may enter the fish trap independently of their depth in the water.

In a preferred embodiment the fish trap includes a plurality of fish traps which in use are vertically staggered with respect to each other.

In many instances the water in the intake of the dam may be quite deep and use of a single fish trap to cover the full depth may be unwieldy or impractical. An advantage of using a plurality of fish traps stacked one on top of the other from the base of the intake up to the surface of the water in the intake, is that each fish trap can be of a size and construction suitable for trapping the target fish. The individual fish traps from the stack may also be easier to handle and manage that one large fish tank.

In a preferred embodiment the fish trap is removable from the water in the intake. Typically this will involve a lifting mechanism which may be located adjacent to the fish trap on a top of the first wall. The lifting mechanism may be operated to lift the fish trap, or a stack of fish traps, out of the water onto the top of the first wall, and to lower the fish trap back into the intake when necessary.

According to another aspect of the present invention there is a method substantially as described above wherein the step of removing the fish trap from the intake is followed by the steps of: h) releasing the first side of the screen from the first wall; and i) rotating the screen about the attachment of the screen to the second wall until the screen is adjacent the second wall of the intake.

An advantage of this arrangement may be that, when not in use, the screen may be rotated about the axis at the second side of the screen to move the screen into a position adjacent the second wall, leaving the remainder of the intake free for water to flow through.

In a preferred embodiment the obstacle is a dam.

It is common for a dam to have an intake which is part of the dam, the intake used to take water through or over the dam. However, it will be appreciated that any obstacle may have an intake; for example where the obstacle is a naturally caused blockage across a river the intake James & Wells ref: 702954/62 could be the river upstream of the obstacle, with the walls of the intake corresponding with the banks of the river and the base of the intake being the river bed.

In a preferred embodiment the dam is part of a hydroelectric power station.

In a preferred embodiment the intake is a turbine bay of a hydroelectric power station located upstream of a penstock screen.

According to another aspect of the invention there is provided a system for trapping and transporting target fish around an obstacle, the obstacle including an intake having a first wall and a second wall connected by a base, the intake being part of a flow path over or through the obstacle, the system including:  a fish trap including a fish trap entrance having a width, and wherein a side or sides of the fish trap include(s) a plurality of apertures which are too small for the target fish to swim through;  a screen having a first portion through which the target fish can swim and a second portion through which the target fish cannot swim, the first portion having a width comparable to the width of the fish trap entrance; and  a lifting mechanism to raise and/or lower the fish trap from/into the intake.

In a preferred embodiment the fish trap includes a plurality of fish traps configured to stack one on top of another.

In a preferred embodiment the system includes a releasable connector configured to releasably attach a side of the first portion of the screen to the first wall of the intake.

In a preferred embodiment the system includes a second connector configured to attach a side of the second portion of the screen to the second wall of the intake, wherein the second connector is configured to allow the screen to rotate about an axis parallel to the side of the second portion of the screen.

It will be apparent to a skilled reader that a similar system may be used downstream of an obstacle, such as a dam, to trap target fish migrating upstream for subsequent transport and release into the water above the obstruction.

BRIEF DESCRIPTION OF THE DRAWINGS Further aspects of the present invention will become apparent from the ensuing description which is given by way of example only and with reference to the accompanying drawings in which: James & Wells ref: 702954/62 Figure 1 shows a schematic plan view of the system according to one embodiment of the invention; Figure 2 shows another plan view of the embodiment of Fig. 1; Figure 3 shows a schematic front view of the embodiment of Fig. 1; Figure 4 shows another front view of the embodiment of Fig.1; Figure 5 shows a schematic side view of the embodiment of Fig.1; and Figure 6 shows a schematic plan view of a position of a screen according to the embodiment shown in Fig. 1.

BEST MODES FOR CARRYING OUT THE INVENTION A system for trapping and transporting fish around an obstacle is generally indicated by arrow 1 in Figures 1 to 5. The obstacle is a dam of a hydroelectric power scheme, the dam generally indicated by arrow 2. The dam includes a spillway 3 (shown closed in Fig.1) for spilling excess water, and an intake in the form of a turbine bay 4. The turbine bay includes a first wall, 5 and a second wall 6 connected together by a base 7 (shown in Fig.3).

A penstock screen 8 is located at the end of the turbine bay adjacent the dam. The penstock screen is used to filter floating debris from entering the turbine chute (not shown). With the spillway closed and the turbine chute open, water from the lake behind the dam is drawn into the turbine bay, as indicated by arrows 9 and 10.

The components of the trapping system are shown in plan view in Fig. 2, and include a fish trap 11, a screen 12 and a lifting mechanism 13.

The fish trap 11 is lowered into the water adjacent the first wall 5 and extends from the base 7 of the turbine bay to the water surface. The fish trap consists of a plurality of fish traps stacked one on top of another as shown in Fig.3. Each trap is typical of the type of trap normally used to catch the target fish. In the present embodiment the traps are eel cages 14. The eel cage 14 has a rigid metal frame onto which mesh is fixed to enclose the eel cage apart from a cage entrance 15. The aperture size of the mesh is too small for the adult eels to swim through.

The cage entrance 15 has a conical shape which tapers away from the front of the cage entrance into the interior of the cage 16. The eels enter through the cage entrance, swim through the conical section and out into the main chamber 17 of the eel cage where they are retained.

James & Wells ref: 702954/62 The fish trap is lowered into and out of the water by a lifting mechanism in the form of a winch 13. While a winch is a convenient mechanism for this purpose it will be apparent that any type of lifting mechanism able to lift the fish trap will suffice (e.g. a crane or derrick). The stack of eel cages may be lowered or lifted together, with individual cages added or removed from the stack as the stack passes above the top of the first wall.

A screen 12 is located in the turbine bay upstream of the fish trap. A frontal view of the system (looking towards the fish trap), is shown schematically in Fig.4. The screen extends from the base 7 of the intake to at least the water surface, and across the intake from the first wall 5 to the second wall 6. The screen includes a screen frame 18 including a dividing strut 19 which separates the screen into a first portion 20 and a second portion 21.

The first portion has a first screen surface 22 and the second portion has a second screen surface 23. The first screen surface 22 is a wire mesh where the apertures of the mesh are sufficiently large to enable an adult eel to swim through the mesh. The second screen surface 23 is also a wire mesh where the apertures of the mesh are too small to enable an adult eel to swim through the mesh. The size of the apertures in each case are determined by the size of the target fish, with the apertures in the first screen surface being large enough so the target fish can swim through the mesh without injury.

The second portion of the screen is inclined with respect to the first portion by approximately 45°. This angle is not critical so reference to an inclination of approximately 45° should not be seen as limiting. In use in the intake the second portion 21 of the screen is upstream from the first portion 20. The purpose of the inclination between the two portions of the screen is to guide the target fish along the (impenetrable) second portion 21 of the screen towards the first section 20 of the screen, which in use is oriented at a right angle to the first wall 5 of the intake.

In this way the first portion of the screen may be placed in close proximity to, or preferably against, the fish trap entrance 15 of each eel cage 14 in the stack of eel cages. Once an eel encounters the first portion 21 of the screen it is able to swim through the first screen surface and into the eel cage 14 through the eel cage entrance 15.

The first side 24 of the screen is attached to the first wall 5 of the intake by a first connector 25 and the second side 26 of the screen is attached to the second wall 6 of the intake by a second connector 27. The first connector 25 is releasable so that this end of the screen is not permanently fixed to the first wall 5. The second connector 27 is configured to allow the screen to rotate about an axis parallel to the second side 26 of the screen. In second connector is located upstream of the first connector. In this manner the first side 24 of the screen can be released and the screen moved to an open position adjacent the second wall 6 by rotating the screen about the second connector 27. In the open position the intake is in its normal operating condition.

James & Wells ref: 702954/62 The location of the first portion 20 of the screen determines the location of the stack of eel cages forming the fish trap 11 and the lifting mechanism 13 located on the top of the first wall 5.

In this embodiment the screen 12 is permanently located within the turbine bay of a hydroelectric power scheme dam. As mentioned previously eels migrate mostly at night, so that the system of trapping the eels does not need to be used during daylight hours.

Accordingly during the day the fish trap is removed from the turbine bay and the screen is in an open position adjacent the second wall of the turbine bay. During this time the spillway gates may be open, so that the dam is in normal operating condition.

As night falls the screen 12 is moved into a closed position, as shown in Fig.s 1-5. The stack of eel crates forming the fish trap 11 are lowered into the turbine bay with the eel crate entrances downstream of, and as close as possible to, the first portion 20 of the screen.

The fish trap is removed from the turbine bay the following morning and the screen moved back into the open position, as shown in Fig.6. The eels retained in the eel crates are loaded onto transport (usually a truck) and taken to a location downstream of the dam (or indeed to any other suitable location) and released back into the water.

The screen 12 includes a walking platform 28 located on the top of the screen frame 18. This walking platform may be used by an operator to inspect and maintain the screen 12, for example to remove floating debris caught on the surface 22, 23 of the screen.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.

James & Wells ref: 702954/62 WHAT I

Claims (7)

CLAIM 1. IS;

1. A method of trapping and transporting target fish around an obstacle, the obstacle including an intake having a first wall and a second wall, the intake being part of a flow path over or through the obstacle, the method including the steps of: a) placing a screen in the intake, the screen having a first portion through which the target fish can swim and a second portion through which the target fish cannot swim; b) placing a fish trap in the intake downstream of the screen, the fish trap being placed in proximity to or against the first portion of the screen, the fish trap having a fish trap entrance which is placed facing the first portion of the screen; c) allowing the target fish to swim through the first section of the screen and into the fish trap entrance; d) retaining the target fish inside the fish trap; e) removing the target fish trap from the intake; f) transporting the retained target fish to a location downstream of the obstacle; g) releasing the retained target fish into the water at the new location.

2. A method as claimed in claim 1 wherein the screen extends from the base of the intake to at least the water surface, and across the intake from the first wall to the second wall.

3. A method as claimed in either one of claims 1 or 2 wherein the screen includes a rigid screen frame extending at least around the perimeter of the screen.

4. A method as claimed in any one of claims 1 to 3 wherein the screen includes a screen surface which spans the entire screen frame.

5. A method as claimed in claim 4 wherein the screen surface includes a plurality of apertures.

6. A method as claimed in either one of claims 4 or 5 wherein the screen surface is in the form of a mesh.

7. A method as claimed in either one of claims 5 to 6 whereinin the apertures in the screen surface of the first portion of the screen are sufficiently large to enable the target fish to swim through. James & Wells ref: