GB2511134A

GB2511134A - Apparatus for assisting the upstream movement of anguillidae

Info

Publication number: GB2511134A
Application number: GB1303394.9A
Authority: GB
Inventors: Mr Nicholas Ian Horton
Original assignee: FOREST OF DEAN STONE FIRMS Ltd
Current assignee: FOREST OF DEAN STONE FIRMS Ltd
Priority date: 2013-02-26
Filing date: 2013-02-26
Publication date: 2014-08-27
Also published as: GB201303394D0

Abstract

Apparatus for encouraging the upstream movement of anguillidae or eels by means of an inclined raceway or ladder. The apparatus comprises an element 18 which forms part of the raceway floor. The element comprises a first plurality of individual upstanding projections (25 figure 2) formed in an array. The projections are spaced from one another, at least in one direction, to allow mature eels to contact facing surfaces to assist in forward movement. The apparatus also comprises an array of intermediate projections (27, 28 & 29 figure 2) between at least some of the first projections. The intermediate projections are smaller than the first projections and positioned such as to form, with the first projections, channels the dimensions of which are smaller than the spacing of the first projections to allow juvenile eels to contact opposite surfaces to assist forward movement.

Description

APPARATUS FOR ASSISTING THE UPSTREAM MOVEMENT OF ANGUILLIDAE

The present invention relates generally to apparatus for assisting the upstream movement of anguillidae.

Anguillidae are a sub-species of the genus Anguilla which includes, among others, eels.

Anguilla are catadromous, spawning in the Sargasso sea and making their way over a period of years to European waters where they spend the majority of their lives growing and maturing in fresh water. As adults they return to the sea to spawn.

On arrival in fresh water areas the eels, mostly juveniles, have to pass upstream to the fresh water areas where they intend to spend their lives.

However, human intervention in the river environment has placed barders to the upstream migration of anguillidae including locks and weirs introduced for navigation purposes, and dams built forwater retention and/or hydro-electric power generation.

These artificial barriers to anguillidae migration have in recent years contributed to a very significant reduction in their numbers, and efforts are now being made to remedy this situation by the provision of by-pass routes especially adapted for the upstream movement of anguillidae. Such routes or pathways are provided in the form of an inclined raceway down which passes a diverted part of the river water, and which has a specially formed bottom surface which provides contact points for upstream movement. In this respect it will be appreciated that anguillidae do not swim" in the same way as fish by acting directly on the water (probably, it is supposed, because of the relatively slim and slight lateral surfaces of the creatures, which do not lend themselves to the application of water pressure) but, rather, they move forward by the lateral engagement of their flanks on upwardly projecting parts of the river bed, such as pebbles and stones, urging themselves forward by this direct contact, lubricated by the flow of water over the pebbles, and assisted by the special form of the skin which encourages unidirectional forces.

Known forms of apparatus for assisting the upstream movement of anguillidae, commonly known as eel ladders, have utilised a number of artificial means for simulating the pebbly or rocky river bottom in the raceway to provide engagement surfaces for the eels to contact in gaining their forward movement. These formations have included the provision of brush-like surtaces similar to so-called "astroturf" (artificial grass). Although this has met with some success, it is not entirely satisfactory or really adequately durable, and other attempts have been used by providing a plurality of upstanding projections spaced from one another in an array of generally cylindrical bosses or columns against which the eels can press as they move against the stream.

The spacing of such projections which suits mature eels, however, is far too great to be of any use to the much smaller juvenile eels, and it must be recognised fhat nof only are the juvenile eels in much greater numbers but it is far more important that these should be assisted in reaching the freshwater regions where they will mature into the adults on which the next generation of eels depends.

The present invention seeks to provide a solution to this problem by providing apparatus for encouraging juvenile anguillidae to move upstream, comprising a base with a plurality of individual upstanding projections in an array, the projections being spaced from one another, at least in one direction, such as to allow eels to contact facing surfaces to assist in advancing movement, in which there are further provided an array of intermediate projections between at least some of the said projections, the intermediate projections being smaller than the said projections and positioned such as to form with the said projections, channels fhe dimensions of which are smaller than the spacing of the said projections such as to allow juvenile eels to contact opposite surfaces thereof to assist in advancing movement.

Expressed more generally, the present invention provides an element for use in assisting the upstream movement of anguillidae, comprising means defining at least one first channel having a first lateral dimension between spaced projections, and means defining at least one second channel having a second lateral dimension, smaller than the first, whereby to provide contact surfaces for the upstream movement of anguillidae of different sizes.

By providing such intermediate elements, typically shorter in height than the main projections, it is possible to provide a lower smaller scale array of contact points for the smaller juveniles to engage without detrimentally effecting the pathway adapted for mature eels.

Conveniently, the said projections are spaced in a rectangular array and in a preferred embodiment of the invention the projections are substantially rectangular in plan. At least some of the said projections may have a curved upper surface, and this curvature may be approximately dome-like which simulates as closely as possible the shape and configuration of naturally-occurring pebbles and stones in the stony bottom of a stream.

By contrast, it is preferred that at least some of the said intermediate projections have substantially flat upper surfaces. This, then, encourages both mature eels and young juveniles to wriggle upstream against the flow of water which, as will be explained, is caused to flow over fhe element in use of the invention.

In a preferred embodiment of the invention the said projections are arranged in rows generally parallel to the intended stream direction in use of the element and the channel between at least two adjacent rows is left free of said intermediate projections whereby to form a channel of larger dimensions in the region between the said two adjacent rows of projections. With less obstruction to its flow the water which, in use, is caused to flow along the element can form a faster-flowing stream which, upon exiting the apparatus provides a signal to the eels that a potential pathway is present; it has been found this encourages the eels to approach the mouth of the apparatus via the stream exits.

As wifh the said projections, at least some of the said intermediate projections may be arranged in rows generally parallel to the intended stream direction in use of the apparatus, and alternate such intermediate projections in a stream direction row may have a greater dimension along the stream direction. Such intermediate projections of greater stream direction dimension are preferably intercalated within intermediate projections having the shorter stream direction dimension, this alternating configuration being repeated transversely of the element as well as longitudinally, in which case the said intermediate projections of shorter stream direction dimensions are located at the intersections of channels between rows of projections extending in the said stream direction and files of projections extending transverse the said stream direction.

The present invention also comprises apparatus for forming an eel ladder composed of an array of elements as defined hereinabove adapted to be placed in a waterway and to receive a stream of water.

The presenf invention also comprehends a method of encouraging juvenile anguillidae to move upstream, comprising the steps of forming a plurality of elements having sets of projections of greater and smaller vertical and transverse dimensions, forming an array of such elements as the bottom of a raceway within a water course, and directing a stream of water down the raceway. The water flowing sown the raceway may be a diverted part of the flow of the watercourse in which the apparatus is located.

One embodiment of the present invention will now be more particularly described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a general perspective view of an eel ladder formed in a watercourse using the elements of the present invention; Figure 2 is an axonometric projection of a single element suitable for use in forming an eel ladder in accordance with the principles of the present invention: Figure 3 is an axial section taken on the line Ill-Ill of Figure 2; and Figure 4 is a transverse section taken on the line IV-IV of Figure 2.

Referring now to the drawings, Figure 1 illustrates a river scene in which a river or stream 11 has adjacent sections 12, 13 being an upper section 12 at a higher level than a lower section 13 and separated by a dam or weir 14 over which water flows steeply and with relatively high force. The river 11 is confined between opposite banks 15, 16 and, in the absence of any other features, the weir 14 would constitute an insurmountable barrier to the upward migration of catadromous anguillidae.

To mitigate this problem there is provided a chute or raceway 17 having a raceway floor made from elements 18 in accordance with the principles of the present invention and which will be described in more detail below, defining a channel 19 between lateral confining sides 20, 21. Water from the upper level or pool 12 can enter the raceway 17 and the level of the entrance is chosen or adjusted such that a relatively thin layer of water flows in the channel 19 and exits at the mouth 22 of the raceway 17 forming an outflowing stream as indicated by the arrows A. Figure 2 illustrates in axonometric projection the form of an individual element which is positioned as in Figure 1 to form the floor of the raceway 17. Each element 18 comprises a monolithic rectangular (or rather, more literally, parallelepiped) block from an upper surface of which are milled longitudinal and transverse channels 23, 24 defined between rows and files of upstanding projections 25. n this context a file of projections 25 will be understood fo mean a line of projecfions exfending along the length of the rectangular element which is parallel to the direction of the stream through the chute or raceway 17 when the element 18 is assembled to form the floor of such a flume, whereas the rows of upstanding projections 25 constitute the line of projections extending transversely of this stream direction.

The prolections in this embodiment are all spaced equally from one another both in the rows and the tiles to torm a regular rectangular array, and the dimensions ct these, in this embodiment at least, are specifically adapted to the anguillidae found in British waters, namely the common eel, for which purpose the projections 25 are spaced by approximately 30mm and stand 25mm above the bottom surface 26 of the element 18 formed by milling the channels 23, 24. Other configurations, particularly with non-symmetric and non-regular spacing may alternatively be used.

Apart from two longitudinal channels 23a, 23b on either side of a central file of projections 25 the floor 26 of the element is clear and unobstructed whereas, between the other rows of element 25 and transversely across the files the channels between adjacent rows of projections have upstanding secondary or intermediate projections 27, 28, 29. The intermediate projections 27 are generally rectangular in planform, their length being approximately the same as the lengthwise or stream direction dimension of the projections 25 and their width being approximately being one third of the width of the longitudinal channels 23.

The intermediate projections 28 are approximately square in planform, theirwidth being substantially the same as that of the elongate row projections 27, and being intercalated along the rows of intermediate projections 27. Transverse projections 29 form rows in the transverse channels, are of substantially the same dimensions as the longitudinal intermediate projections 27, and, with the exception of the rows 23a, 23b, are located at the intersections of the channels 23, 24 as can be seen in Figure 2.

When positioned with other like such elements 18 to torm a floor of a chute or raceway 17 as illustrated in Figure 1, the channels 23a, 23b provide an unrestricted pathway for the water allowing it to flow slightly faster than at the edges, defined between the sides 20, 21 and thereby generate a stream represented by the arrows A in Figure 1. of slightly greater velocity thereby providing an indication to eels in the lower pool 13 of stream movement, which attracts their attention.

Adult eels can then migrate upstream using the sides of the projections 25 against which to press in performing their sinuous progression, whilst juvenile eels, which are of considerably smaller dimensions, can progress upstream in the lateral parts of the flume 17 in the spaces between the main projections 25 and the intermediate projections 27, 28, 29.

By making the elements 18 from a single block of stone the durability of the flume against the erosion caused by flowing water can be guaranteed and, once fitted, such eel ladders will be expected to have a very extended life avoiding the need for replacement. The use of natural materials also constitutes an ecological advantage over those prior art devices using plastics or other artificial materials which are prone to contamination by bacteria and fungal growth, thereby rendering themselves in need of replacement frequently.

Although an embodiment with a regular array of rows and files has been described, alternative embodiments may present irregular, sinuous, or other non-rectilinear patterns to encourage the upstream movement of anguillidae.

Claims

CLAIMS1 Apparatus for encouraging the upstream movement of anguillidae, comprising an element having a plurality of individual upstanding projections in an array, the projections being spaced from one another, at least in one direction, such as to allow mature eels to contact facing surfaces to assist in advancing movement, in which there are further provided an array of intermediate projections between at least some of the said projections, the intermediate projections being smaller than the said projections and positioned such as to form, with the said projections, channels the dimensions of which are smaller than the spacing of the said projection such as to allow juvenile eels to contact opposite surfaces thereof to assist in their advancing movement.
2. An element as claimed in claim 1 in which the said projections are spaced in a rectangular array.
3. An element as claimed in claim 1 or claim 2, in which the said projections are substantially rectangular in plan.
4. An element as claimed in any of claims ito 3, in which at least some of the said projections have a curved upper surface.
5. An element as claimed in claim 4, in which at least some of the said projections have a domed upper surface.
6. An element as claimed in claim 5, in which substantially the entirety of the said projections have a domed top.
7. An element as claimed in any preceding claim, in which at least some of the said intermediate projections have substantially flat upper surfaces.
8. An element as claimed in any preceding claim, in which the said projections are arranged in rows generally parallel to the intended stream direction in use of the element, and in which the channel between at least two adjacent rows is free of said intermediate projections whereby to form a channel of larger dimension in the region between the said two adjacent rows of projections.
9. An element as claimed in any preceding claim, in which the said intermediate projections are arranged in an array comprising rows generally parallel to the said stream direction and files generally transverse the said streams direction.
10. An element as claimed in any preceding claim in which some of the said intermediate projections are arranged in rows generally parallel to the intended stream direction in use of the element.
11. An element as claimed in claim 10, in which alternate said intermediate projections in a stream direction row have a greater dimension along the stream direction.
12. An element as claimed in claim 11, in which the intermediate projections of greater stream direction dimension are intercalated with intermediate projections having a shorter stream direction dimension.
13. An element as claimed in claim 12, in which the said intermediate projections of shorter stream direction dimension are located at the intersections of channels between rows of projections extending in fhe said stream direction and files of projections extending transverse the said stream direction.
14. An eel ladder element substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.
15. An eel ladder comprising an array of elements as claimed in any of claims 1 to 14 within lateral walls in a waterway.
16. An element for use in assisting the upstream movement of anguillidae, comprising means defining at least one first channel having a first lateral dimension between spaced projections, and means defining at least one second channel having a second lateral dimension, smaller than the first, whereby to provide contact surfaces for the upstream movement of anguillidae of different sizes.