Abstract:
A fish pass comprises material ( 1 ) that augments a significant part of the crest of a water penning control structure ( 11 ) and a channel component ( 3 ) to convey water downstream of the water penning control structure ( 11 ), the channel component ( 3 ) having a hinged attachment to the crest of the water penning control structure ( 11 ).

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to fish passes, i.e. devices that allow upstream migration of fish over water level regulation devices such as tilting weirs, twin leaf gates and other water penning structures. The invention has been developed in relation to eel passes, but has application to fish passes generally. 
         [0002]    As part of their life cycle, eels migrate upstream in rivers, which are highly regulated resources with many control structures on them. These control structures pen back water at certain times of the year and allow flood water to dissipate at other times. Historically, these structures were of timber and/or were of such an age that their wetted surfaces were covered with moss and other natural materials in which the eels could get purchase and ascend such surfaces. 
         [0003]    There has, however, been a recent move to replace traditional penning devices with modern stainless steel and plastic structures. Examples of these are the tilting weir and the twin leaf gate. These latter kinds of structures prevent upstream migration of eels by virtue of their sheer, smooth sides and confusing overflow characteristics—eels navigate over more natural barriers by moving upstream against an attracting flow through a suitable substrate. 
         [0004]    Large scale eel passes use a pumped water flow as an attractant, but they are only viable on very large in-river barriers, are expensive to run and the pumps frequently clog. 
         [0005]    It is accordingly an object of the present invention to provide an improved form of fish pass. 
       SUMMARY OF THE INVENTION 
       [0006]    According to the present invention there is provided a fish pass which comprises material that augments a significant part of the crest of a water penning control structure and a channel component to convey water downstream of the water penning control structure, the channel component having a hinged attachment to the crest of the water penning control structure. 
         [0007]    A buoyancy unit is preferably attached adjustably to the channel component. 
         [0008]    The channel component is preferably lined with a bristle substrate, and the bristle substrate is preferably not parallel to the base of the channel component. 
         [0009]    The fish pass may also include an upstream element that is movable pivotally relative to the channel component, and a gearbox unit may be provided for effecting controlled movement of the upstream element relative to the channel component. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a perspective view of an eel pass in accordance with a first embodiment of the present invention, 
           [0011]      FIG. 2  is a side elevation of the eel pass of  FIG. 1  mounted on a tilting weir gate showing how the eel pass functions at two different water penning heights, 
           [0012]      FIG. 3  is a sectional view of the main channel of the eel pass of  FIG. 1 , showing different substrate arrangements and different channel widths, 
           [0013]      FIG. 4  is a sectional view of part of a tilting weir gate, showing typical attachment options for the weir crest augmentation material, 
           [0014]      FIG. 5  is a perspective view of an eel pass in accordance with a second embodiment of the present invention, 
           [0015]      FIG. 6  is a perspective view of a gearbox that forms part of the eel pass of  FIG. 5 , 
           [0016]      FIG. 7  is a perspective view of the gearbox of  FIG. 6 , but with the housing cover removed, and 
           [0017]      FIG. 8  is a reverse perspective view of the gearbox of  FIG. 6 , with the housing cover and the shaft-end housing removed. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0018]    The eel pass shown in  FIGS. 1 to 4  of the drawings comprises two strips  1  of weir crest augmentation material that are attached by suitable fixings  8 ,  13  to the crest of a tilting weir  11  or other appropriate water level control structure. A main channel  3  is hingedly connected at  2  to the weir crest augmentation material, with the hinge being at substantially the same level as the top of the tilting weir  11 . The channel  3  is thus arranged for pivotal movement relative to the non-augmented section of the weir crest. The inside of the main channel  3  is lined with an appropriate bristle substrate  7  and the ends of the main channel  3  are partially blanked off by means of triangular end stops  6 . The bristle substrate  7  carries two densities of bristles to cater for different sizes of eels and the bristle substrate  7  is fixed in a sloping arrangement to allow for different water flow rates down the channel  3 . The bristles are thus inclined to the vertical so that, in cross-section, the upper surfaces of the bristles are either of V-shaped formation, or inverted V-shape, as shown in  FIG. 3 . 
         [0019]    The two strips  1  of weir crest augmentation material, which may be of wood or a suitable plastics material, effectively serve to raise the height of the weir for substantially the whole width of the weir so that the majority of the water flowing over the weir passes down the channel  3 . 
         [0020]    There is a planar lid or cover component  7 A that is hingedly or otherwise attached to the main body of the channel  3  and this protects the ascending eels from desiccation and predation. The lid or cover component  7 A is removable to facilitate cleaning of the eel pass. 
         [0021]    Adjacent the downstream end of the channel  3  of the eel pass, there is an adjustable buoyancy unit  4  in the form of a hollow cylinder that is attached by means of an adjustment carriage  5  to guide slots in the sides of the main channel  3 . The flotation effect of the buoyancy unit  4  can be adjusted for varying conditions by moving the carriage  5  along the guide slots. 
         [0022]    The eel pass includes an upstream element  10  that is hingedly connected at  9  to the weir crest augmentation material, with the hinge being at substantially the same level as the top of the tilting weir  11 . The upstream element  10  also has a covering of bristle substrate and the function of the upstream element  10  is to ensure that eels which have passed up the main channel  3  can get far enough away from the weir flow that they do not get swept back downstream. The upstream element  10  may be fixed at a pre-set angle or may be adjustable by altering its weight or profile. 
         [0023]    The tilting weir  11  is arranged to pivot about a pivot axis  12  and  FIG. 2  shows how, with the tilting weir  11  arcing around the pivot point  12 , the eel pass will still maintain a water flow down the channel  3  which will remain at a suitable gradient. The line indicated at W 3  in  FIG. 2  represents the downstream water level while the lines W 1  and W 2  represent two different penned water levels. 
         [0024]      FIG. 4  illustrates two possible methods of attaching the weir crest augmentation material  1  and the hinges  2  and  9  to the top surface of the weir  11  or other water penning control structure. Fixing screws  8  can be driven through the weir crest augmentation material  1  into the body of the water penning control structure  11 , or an appropriately dimensioned H-section extrusion  13  can be attached to the structure  11 , with the weir crest augmentation material  1  attached to the H-section extrusion  13 . 
         [0025]    An important advantage of the eel pass described above and shown in  FIGS. 1 to 4  is that it can easily be retro-fitted to existing structures in situ rather than replacing the entire tilting weir  11  or other water level control structure. The eel pass can also be factory fitted for a new installation. 
         [0026]    Although specific reference has been made to the use of the device of the present invention to assist upstream movement of eels, the pass can be used to assist upstream movement of fish generally. 
         [0027]    The eel pass (or fish pass) shown in  FIGS. 5 to 8  differs from that shown in  FIGS. 1 to 4  in that it includes a gearbox unit for effecting relative movements of the components of the eel pass. The purpose of the gearbox unit is to transmit the effects of a change in weir angle, registered by the downstream end of the eel pass, to the upstream component, thereby ensuring that this component is always angled downwards into the upstream water body. 
         [0028]    This will allow eels or other fish to ascend the pass to its apex and enable them to crawl or swim beyond the influence of the weir crest flow. 
         [0029]    The whole gearbox unit can be raised or lowered according to water flow conditions and the position or influence of the weir crest augmentation material. 
         [0030]    As shown in  FIGS. 6 to 8 , the gearbox unit that comprises gears G 1 , seated in a gear housing G 2  to which a gear housing cover G 2   a  is attached. The gearbox unit includes a downstream shaft G 3 , which is the attachment point for the downstream element of the eel pass. This shaft G 3  transmits movement from a tilting weir in relation to the downstream element  3  of the eel fish pass to the appropriate gear. Because the gears G 1  are interlinked this movement is transferred to an upstream shaft G 4 . The upstream element  10  of the eel pass is attached to this shaft G 4  and deflects accordingly. The size and number of gears G 1  can be calculated to provide an approximately constant downwards angle in the upstream element of the eel pass, regardless of the tilting angle of the weir. 
         [0031]    Both shafts G 3  and G 4  are supported on the non-geared side by a shaft-end housing G 5 . The gears G 1  in their housing G 2 , the shafts G 3  and G 4  and the shaft-end housing G 5  can all be raised and lowered in relation to a weir fixing bracket G 6  by the rotation of adjuster screws G 7  and G 8 . Rotation of the screws G 7  and G 8  will allow either more or less water to flow down the eel pass. The adjuster screws G 7  and G 8  pass through captive threaded blocks G 9  and G 10  which are recessed into housings G 2  and G 5 . The adjuster screws G 7  and G 8  terminate in the weir bracket G 6  and the raising and lowering action is stabilized and supported by four guide pins G 11 , G 12 , G 13  and G 14 . These guide pins are fixed into the weir bracket G 6 . 
         [0032]      FIG. 5  shows the gearbox unit of  FIGS. 6 to 8  attached to and acting between a downstream main channel component  3 , to which a buoyancy unit  4  is adjustably attached, and an upstream channel component  10 , with bristle assemblies contained within both channel components  3  and  10 .