Abstract:
Provided are a device and associated method for simulating natural hydraulic cues received instinctively by waterborne fauna. A preferred embodiment is suitable for modifying existing manmade barriers such as fish diversion screens used at dams. The simulated cues mimic those produced by the flow of water over rough streambeds. Fish detect the cues and avoid contact with the barriers in the same way that they avoid collision with natural features. In one embodiment, a series of rectangular plates are attached to the U-clip connectors on the downstream side of diversion screens. The plates are oriented approximately perpendicular to the flow lines approaching the surface of the screen. The flow contacts the plates and, because the orientation of the plate creates an unstable hydraulic field, the flow alternately slips above and below the plates, creating fluctuating local acceleration zones able to be detected by migrating fish and other waterborne fauna.

Description:
STATEMENT OF GOVERNMENT INTEREST  
       [0001] The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The field is that hydraulic engineering needed to guide, regulate, and modify fluid flow. In particular, a preferred embodiment of the present invention assists waterborne fauna, such as fish, in avoiding contact with a manmade obstruction.  
         BACKGROUND  
         [0003]    Water resources development typically includes the construction of dams across rivers to impound and regulate flows for power production, flood control, water supply, irrigation and other economically beneficial uses of water. In many rivers, adult fish typically migrate upstream through the river to spawn and rear in upstream areas. Once young, or juvenile, fish reach a certain size they instinctively migrate downstream to the adult habitat areas in downstream reaches of the river, in lakes, or in the ocean where they mature into adults and complete their life cycle. Juvenile salmon and many other juvenile fishes are spawned in upstream fresh water systems where early life stages are completed but reach adulthood in downstream areas.  
           [0004]    Unfortunately, dams block the migration of fish and thereby interfere with the completion of their natural life cycles. Sustainable water resources development is often facilitated by the use of hydraulic structures to pass these juvenile fish around the dam and other channel obstructions.  
           [0005]    Systems and methods for assisting fish in circumventing man-made barriers in streams have been tried for many years, e.g., U.S. Pat. No. 3,338,056, Fingerling Saving System, issued to Roscoe, Aug. 29, 1967, details a complex arrangement of recesses using vertically oriented entrances for permitting the transport of fingerlings around a dam. Quoting from the &#39;056 patent: “The difficulty (of getting fingerlings downstream) arises due to the tendency of the fingerlings to follow flowing currents of water, and ordinarily such flowing currents go through the turbines of the associated power station. The fingerlings suffer high mortality in passing through the turbines. . . .”  
           [0006]    A later patent, U.S. Pat. No. 4,437,431, Method and Apparatus of Diversion of Downstream Migrating Anadromous Fish, issued to Koch, Mar. 20, 1984, uses an “artificial stream” generated by water jets within the natural stream together with long tubes having funnel-shaped entrances located on the sides of the stream at some distance from the upstream side of the dam. Another solution that offers an “attracting” artificial current based on an active source include a propeller generated current as described in U.S. Pat. No. 6,102,619, Flow Inducer Fish Guide and Method of Using Same, issued to Truebe et al., Aug. 15, 2000. A related technique involving a series of opening and closing valves, fish passing actuators and conduits is detailed in U.S. Pat. No. 6,273,639 B1, Method and Apparatus for Facilitating Migration of Fish Past Dams and Other Barriers in Waterways, issued to Eikrem et al., Aug. 14, 2001.  
           [0007]    To comply with government regulations, other solutions have involved configurations of barrier screens and bypass conduits such as that envisioned by U.S. Pat. No. 4,481,904, Fish Conservation Device, issued to Fletcher, Nov. 13, 1984; U.S. Pat. No. 4,526,494, Penstock Fish Diversion System, issued to Eicher, Jul. 2, 1985; and U.S. Pat. No. 4,740,105, issued to Wollander, Apr. 26, 1988. One such screen barrier uses a number of like modules in a ladder arrangement affixed to the bottom of the channel as described in U.S. Pat. No. 4,929,122, Fish Protection System for Dams, issued to Yoas, May 29, 1990. An underwater “screen house” located adjacent a dam is described in U.S. Pat. No. 5,385,428, Water Intake Fish Diversion Apparatus, issued to Taft et al., Jan. 31, 1995. A buoyant screen that may be sunk and raised at appropriate fish migrations times is described in U.S. Pat. No. 5,558,462, Flat Plate Fish Screen System, issued to O&#39;Haver, Sep. 24, 1996.  
           [0008]    Still other solutions provide for a buoyant arrangement of vertically oriented slats located some distance upstream from a barrier such as described in U.S. Pat. No. 5,263,833, Fish Guiding Assembly and Method Utilizing Same, issued to Robinson et al., Nov. 23, 1993. This arrangement, and others like it, consumes a considerable amount of the surface area immediately upstream from the dam.  
           [0009]    Active solutions are also proposed as exemplified in U.S. Pat. No. 5,445,111, Electrified Fish Barriers, issued to Smith, Aug. 29, 1995, describing linear curtain arrays characterized by pulsed driving signals that may use varying voltages. Other active solutions include complex electronic detectors and control systems to alter the operation of a hydroelectric powerhouse in the presence of migrating fish as described in U.S. Pat. No. 6,038,494, Control System for Enhancing Fish Survivability in a Hydroelectric Power Generation Installation, issued to Fisher et al., Mar. 14, 2000.  
           [0010]    Fish ladders have been used to help returning anadromous fish get to spawning beds and are also proposed to help the juveniles return to the sea as described in U.S. Pat. No. 6,155,746, Fish Ladder and Its Construction, to Peters, Dec. 5, 2000. This details a complex series of basins having vertical inflow and outflow slots for transporting fish around a barrier.  
           [0011]    The above solutions involve a configuration that is either much more complex and costly than a preferred embodiment of the present invention, uses much more “geography” to effect the desired result, uses energy or large quantities of water to effect the desired result, is unable to be used to modify an existing barrier, or a combination of these undesirable factors.  
           [0012]    Juvenile outmigrating fish instinctively seek passage through the dam when their downstream journey is blocked. For a detailed discussion, refer to U.S. Pat. No. 6,160,759, Method for Determining Probable Response of Aquatic Species to Selected Components of Water Flow Fields, issued to Nestler et al., Dec. 12, 2000, and incorporated herein by reference. In the Columbia River, conventional surface bypass collectors (SBC&#39;s) are a preferred passage design used at dams for passing outmigrating juvenile fish.  
           [0013]    A conventional SBC employs a water intake plume to attract fish to its entrance. Using conventional engineering concepts, the SBC&#39;s attract and concentrate fish for conveyance around the dam in a manner that helps prevent their entry into turbines or other high-energy hydraulic conditions where they may be injured or killed. An SBC uses an attracting intake plume of sufficient flow magnitude to overcome the attracting flow of competing inflows such as are present at hydroturbines, sluicegates or spillways. Once juvenile fish enter the SBC they are conveyed to a bypass channel where they continue the migration downstream of the dam. Design of the entrance hydraulic conditions used in conventional SBCs does not incorporate knowledge of the behavior of the juvenile fish in natural streams and rivers. As a consequence, the performance of conventional SBCs varies, with some working well and others not. Poor performance most commonly results from uncertainty about the flow conditions required to attract juvenile fish to the entrance of the SBC. A preferred embodiment of the present invention provides a method that employs natural hydraulic cues.  
           [0014]    To protect fishes that are not intercepted by an SBC, or if an SBC is not available, the present state-of-the-art for fish protection uses diversion screens  300  to intercept fish and prevent them from entering intakes of turbines or diversion canals. For example, FIG. 1 illustrates typical structures commonly encountered by fish as they attempt to move from the forebay on the upstream side of a dam to downstream river reaches. The dam depicted consists of a powerhouse  101  and a spillway  102  with water flow indicated by arrows  103 . Once the water passes the dam, it and its contents are dumped into the tailrace  104 .  
           [0015]    [0015]FIG. 2 shows design features (through cut A-A of FIG. 1) of a conventional system used to intercept outmigrating fish. A portion of the flow  103  and surface oriented fish pass through a trash rack  203  and some fish are intercepted by the diversion screen  206  and guided up into a gatewell  202 . A barrier screen  201  returns the majority of the flow back into the turbine  204  for subsequent discharge through the draft tube  205  and concentrates the diverted fish in the gatewell  202 . From the gatewell  202 , outmigrating fish are collected using several different means and conveyed around the dam.  
           [0016]    Refer to FIG. 3. There are three primary design criteria for diversion screens  300 . The first is hydraulic efficiency, i.e., screens  300  should be designed to minimize energy loss across their surface, thereby maximizing energy potential for associated hydropower facilities. Second, screens  300  should be designed so that approach water velocity  103  is low enough so that fish do not impact the screen  300  at damaging velocities. The approach velocity  103  is partially controlled by a perforated plate  302  that is installed behind (downstream) of the screen surface  301 . The size and spacing of the perforations  306  on the plate  302  may be adjusted to vary the water velocity approaching the screen surface  301 . Third, the wires or bars  304  that constitute the screen surface area are spaced  303  so that fish of a certain minimum size are blocked by the screen  300  and physically prevented from passing through the screen  300 . The flow pattern approaching the screen surface  301  is determined by the following characteristics of the system: discharge passing into the intake; the size and shape of the intake; the angle of deployment of the screen  300 ; the size, shape, and spacing of the bars  304  or wires that comprise the screen surface  301 ; the size, shape and location of structural members  304 ,  305  that make up the screen  300  frame; and the size and spacing of the perforations  306  in the back plate  302 .  
           [0017]    The design criteria for minimizing head loss can have significant effects on fish that approach the screen surface  301 . Refer to FIG. 4. A byproduct of increased screen efficiency is that less of the energy of the water passing through the screen  300  is available to generate secondary hydraulic cues that fish can use to detect and avoid the screen surface  301 . Therefore, as hydraulic efficiency increases the screen  300  becomes more hydrodynamically transparent so that fish become more likely to contact the screen surface  301  where they may be injured or killed. In response, the perforation plate  302  must be redesigned or other steps must be taken to decrease approach velocities  103 .  
           [0018]    A need, therefore, exists for an optimum method of guiding migrating fish, in particular juvenile fish, in a way that minimizes the propensity of fish to impact diversion screens. A further need exists to modify existing barriers to reduce the cost of implementing the optimum method.  
         SUMMARY  
         [0019]    A structure and method of adding natural hydrodynamic cues to manmade barriers in waterways is provided. It simulates those cues produced by the flow of water over rough streambeds. Fauna, such as fish, detect the cues and avoid high velocity impact on the barrier surface in the same way that they avoid collision with natural, solid features of the streambed.  
           [0020]    The method that thus assists waterborne fauna adds at least one feature to existing barriers (or conventional barrier designs) that enables simulation of natural hydraulic cues of which fauna are receptive. The simulated cue initiates an instinctive awareness in the fauna, e.g., migrating juvenile fish, to detect and thereby avoid barriers such as fish diversion screens at a dam. The absence of such a feature may result in the fauna contacting barriers at harmful velocities.  
           [0021]    For conventional fish diversion screens, adding a feature comprises affixing rows of elements to the downstream side of the diversion screens. The elements, such as rectangular plates are arranged with a longest dimension approximately perpendicular to the longest dimension of the material that comprises the diversion screens, e.g., wire or bars. The plates are affixed to the diversion screens in spacing and dimension by using standard engineering methods that may also accommodate requirements not related to simulating the natural hydraulic cue. A convenient location for affixing the plates on conventional diversion screens is at the U-clips that both locate (space) and connect the wires or bars to construct the planar diversion screen.  
           [0022]    The diversion screen that results from incorporating a preferred embodiment of the present invention in a conventional design generates a natural hydraulic cue that permits fauna to avoid contact with the screen. It may be built from material such as parallel wires or bars that are much longer in one dimension than in any other dimension, and much smaller in its smallest dimension than in any other dimension. A series of connectors, such as U-clips, connect the elements in parallel, in accordance with a pre-specified spacing assigned between the smallest dimension of each element. This yields a planar structure, i.e., a screen, with a minimum pre-specified spacing between any two elements. So far a conventional diversion screen has been described. A second series of parallel elements, such as rectangular plates, is affixed on the downstream side of the planar structure proximate the connectors (U-clips in some designs). Orienting these rectangular plates approximately perpendicular to the longest dimension of the bars or wires of the screen enables a natural cue to be generated by the heretofore conventional screen design in the sense that the resulting upwelling resembles water flowing over a rock or other channel feature.  
           [0023]    Conveniently, existing barriers or screens may be modified using a preferred embodiment of the present invention. Affixing supplemental structure in accordance with the present invention, enables a diversion screen to generate a natural cue for receipt by select fauna otherwise susceptible to harmful impact on barriers such as fish diversion screens. The supplemental structure is attached to a downstream side of a barrier or diversion screen in such a manner that the resultant Natural Cue Diversion Screen (NCDS) creates localized, dynamic hydraulic features simulating those features that fauna use to instinctively avoid natural barriers in waterways. A proper distribution of elements, such as rectangular plates, provides a pattern of natural hydraulic cues across the entire surface of the diversion screen. The plates may also replace a perforated back plate of a conventional design, thus performing double duty by reducing the flow of water through a surface of the diversion screen to a predetermined quantity.  
           [0024]    A preferred embodiment of the present invention provides a design that enables the generation of natural hydraulic cues. In one embodiment, modifying existing conventional fish diversion screens, the modification adds a series of rectangular plates attached to U-clips. These U-clips are welded on the bottoms of the bars or wire of the conventional screen for structural support and spacing of the individual bars that are the basic elements of the screen. The plates are oriented so that they are approximately perpendicular to the flow lines approaching and passing through the screen surface. A portion of the flow collides with the plates to create locally unstable hydraulic features that chaotically slip above and below the plates. This chaotic hydrodynamic oscillation extends above the screen surface and can be detected by fish prior to a possible relatively high velocity contact with the screen surface. Fish are thereby guided by the signals generated by the modified screen thus reducing unheralded collisions with the screen surface or supporting structure. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 depicts a dam having both a powerhouse and a spillway that may use a prior art fish diversion screen.  
         [0026]    [0026]FIG. 2 shows prior art means incorporated in the powerhouses of the dam of FIG. 1 for diverting fish migrating downstream.  
         [0027]    [0027]FIG. 3 is an isometric view from the surface of a prior art bypass screen showing the individual wedge wires or bars that form the surface of the screen as well as a perforated screen that may be used also.  
         [0028]    [0028]FIG. 4 depicts isometric and side views of streamlines created by the structure of a prior art screen.  
         [0029]    [0029]FIG. 5 is a schematic representation of natural stream cross sections incorporating velocity vectors in three dimensions.  
         [0030]    [0030]FIG. 6 depicts vectors representing stream flow in a natural streambed in both the horizontal and vertical planes with respect to stream flow.  
         [0031]    [0031]FIG. 7 depicts isometric and side views of stream lines passing through a screen with rectangular plates attached to one of the legs of the U-clips in accordance with a preferred embodiment of the present invention.  
         [0032]    [0032]FIG. 8 is a schematic, idealized representation of disruptions in a flow pattern across a screen surface of a preferred embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0033]    Outmigrating juvenile salmon and fish of other species make use of hydraulic cues to navigate their way through the complex flow fields of natural waterways, particularly in muddy water or at night. Many juvenile fishes migrate at night when vision is diminished.  
         [0034]    Refer to FIG. 5. By convention, the x-direction velocity vector, u  503 , is parallel to the long axis of the stream channel  500 , the y-direction velocity vector, v  504 , is perpendicular to u  503  and extends from one shore  501  to the other, and the z-direction vector, w  505 , is perpendicular to both u  503  and v  504  and represents velocity with respect to depth (or elevation) within the stream channel  500 .  
         [0035]    Refer to FIG. 6. Shown are the x-direction vectors, u  503 , with respect to the sides  501  of the channel  500  and also with respect to the top and bottom of the channel  500  and the respective boundaries  602  in each orientation. For example, u  503  at a particular depth  601  is depicted in the cross section on the left and u  503  is depicted near the center of the channel  500  over the entire depth of the channel  500  in the cross section on the right. In natural waterways, water velocities at boundaries  602  are essentially zero and increase away from the boundaries  602  (e.g., where the water comes in contact with the stream bottom or sides) to a maximum value  603  equidistant from the friction effects of the boundaries  602  (after the effect of the boundaries  602  has been corrected for differential roughness). The rate of change in u  503  laterally (Δu/Δy), or with depth (Δu/Δz), has its greatest absolute values near the boundaries  602  and its smallest values at the belly of the velocity profiles  603 . In addition to being the zone of maximum mean water velocity, this zone is also the zone where the change in u velocities in either the z- or y-directions is essentially zero, or in mathematical terms, Δu/Δy=0 and Δu/Δz=0. A fish swim path selection behavior that minimizes the absolute value of Δu/Δy and Δu/Δz will allow a fish  604  to find and maintain its position in this critical zone of optimal migration efficiency in natural waterways.  
         [0036]    Refer to FIGS. 5 and 6. The natural flow fields of streams under steady-state conditions, i.e., not varying with time, can be represented as velocity vectors u  503 , v  504 , and w  505 . The acceleration terms, a u , a v , and a w , representing the acceleration associated with the u  503 , v  504 , and w  505  velocity vectors, may also play a role. In natural waterways, u  503 , v  504  and w  505  water velocities at boundaries  602  such as the sides, top and bottom of the channel  500  are essentially zero because of friction and increase away from the boundaries  602  to a local maximum  603  approximately equidistant from the friction effects of the boundaries  602 . This zone is of critical importance to migrating fish because it represents, on average, the greatest velocity in the cross section  502  and the swim pathway to the ocean that requires the least expenditure of energy by outmigrating fish  604 . In addition to minimizing swimming effort to the ocean, this zone maximizes the size of the sensory envelope within which fish  604  are able to detect and avoid predators, and maximizes their ability to detect and orient to hydraulic cues. Fish  604  that can find this zone are able to utilize the optimum pathway through complex stream or waterway channels  500  to their adult habitat.  
         [0037]    Refer to FIG. 6. The rate of change in velocity vectors is embodied in the hydraulic strain rate or tensor variables, primarily Δv/Δx, Δw/Δx, Δv/Δz, Δa v /Δx, Δa w /Δx, Δa u /Δy, Δa w /Δy, Δa u /Δz, and Δa v /Δz. For example, u  503  velocities in the y-direction (Δu/Δy) or u  503  velocities in the z-direction (Δu/Δz), have their greatest absolute values near the boundaries  602  and their smallest values at the belly  603  of the velocity profiles. Outmigrating juvenile fish  604  have evolved a sensory system that cues into this natural velocity pattern to find the optimum pathway through the waterway. That is, outmigrating fish select the swim path through the waterway that minimizes the absolute value of the tensor variables in the flow field. In particular, they probably minimize the absolute value of Δu/Δy and Δu/Δz, and by so doing are able to locate themselves in the deepest part of the channel  500  about equidistant from both shores  501 . In addition to being the zone of maximum mean water velocity, this zone is also the zone where the change in u velocities in either the z- or y-directions is essentially zero, or in mathematical terms, where Δu/Δy=0 and Δu/Δz=0. A fish swim path selection behavior that minimizes the absolute value of Δu/Δy and Δu/Δz will allow a fish to find and maintain its position in this critical zone of optimal migration efficiency in natural waterways.  
         [0038]    Refer to FIG. 3. A diversion screen  300  that is hydraulically efficient will have a minimal effect on the flow field. Therefore, a migrating fish  604  approaching the screen surface  301  will conclude that the optimum migratory pathway to the ocean passes through the screen surface  301 . Thus, migrating fish  604  may be unable to detect the presence of the screen  300  and are likely to collide with it. The innovative design for a preferred embodiment of the present invention, the Natural Cue Diversion Screen (NCDS), capitalizes on the ability of juvenile fish  604  to respond to the strain rate variables to keep from colliding with rocks and similar features of the solid boundaries  602  of the waterway channel  500 . Refer to FIGS. 3 and 8. The NCDS incorporates specific design features that create small-scale hydrodynamic disturbances or signals (black areas)  801  above the screen surface  301  that signal the presence of the screen surface  301 . The signals allow the fish  604  to detect the screen surface  301  prior to colliding with it. Fish  604  are then guided by the hydrodynamic signals  801  generated by the screen  300  as opposed to being “guided” by the physical structure of the screen  300  itself.  
         [0039]    Refer to FIG. 3. In conventional screens, U-clips  305  are grooved and each individual wedge wire or bar  304  is inserted into the U-clip  305  and welded into place. Refer to FIG. 4. The direction and speed of flow  403  passing through the screen surface  301  between the U-clips  305  is little impacted as indicated at  402  by the presence of the screen  300 . The direction of flow  402  approaching at the U-clips  305  is slightly re-directed away from the screen  300  before re-directing back into the screen surface  301 .  
         [0040]    Refer to FIGS. 7 and 8. Short sections of rectangular plates  701  are attached on the downstream side of the screen  300  (underneath as shown in FIG. 7) and generate unsteady features on the screen surface  301  that are maximally sized and depicted as the black objects  801  on the screen surface  301 . The features of the black objects  801  are drawn as if they are all of the same size and exist as steady state features. In reality, all of the black objects  801  are chaotically fluctuating in size and duration to create a hydrodynamic pattern on the screen surface  301  that signals the presence of the screen  300  to approaching animal life, in particular juvenile fish  604 . This is the natural hydraulic cue now being simulated by the screen  300  as modified in accordance with aspects of a preferred embodiment of the present invention. Note that the streamlines  703  are significantly re-directed by the rectangular plates  701 . Although drawn as a stable, steady family of stream lines  703 , the actual stream lines are changing as the flow  703  alternates chaotically between passing above  704  and below  705  the rectangular plate  701 .  
         [0041]    Thus, in one embodiment, the design feature added to a conventional fish diversion screen  300  that signals the presence of the screen surface  301  to animal life, including juvenile fish  604  consists of a series of evenly-spaced rectangular plates  701  that are attached via a weld  702  or similar mechanism to the slotted U-clips  305  that determine the spacing between the individual wedge wires or bars  303 . The rectangular plates  701  are oriented so that they are approximately perpendicular to the flow lines  703  approaching the screen surface  301 , thus creating a local instability in the flow field. This instability is characterized by the local flow randomly or chaotically passing above and below the screen surface  301 . This hydrodynamic oscillation extends above the screen surface  301  creating chaotically fluctuating local increases in the strain rate variables and turbulence similar to what a fish  604  may encounter in a natural waterway. These small-scale flow instabilities can be detected by fish  604 , and possibly other animal life, prior to untoward physical contact with the screen surface  301  in the same way that fish  604  instinctively avoid colliding with objects in natural waterways.  
         [0042]    Refer to FIGS. 7 and 8. The screen surface  301 , instead of being characterized by efficient flow through the individual wedge wire or bar elements  303 , is now characterized as a complex mosaic of fluctuating small scale turbulent features  801 . If properly sized and spaced, the plates  701  may be used to control flow  703  through the screen surface  301  instead of relying on the perforation plate  302  as is done conventionally. Additionally, the plates  701  may maintain relatively constant total discharge through a screen surface  301  as total flow  703  approaching the screen surface  301  increases because the size of the hydrodynamic instability created by the plates  701  increases as the local water velocity increases. That is, as the discharge (and thereby the water velocity) increases, the size of the hydrodynamic features created by the plates  701  also increases, limiting further flow through the screen surface  301 . Standard engineering practice may be used to determine optimum combinations of screen  300  deployment angle, spacing of the modified screen members  304 ,  305 ,  701  and design of the perforation plates  302  (if still used). The height, length, location, and shape of the plates  701  nominally attached to the U-clips  305  may be adjusted to create the desired hydrodynamic signatures on the screen surface  301 , also using standard engineering methods.  
         [0043]    While the present invention has been described in connection with the preferred embodiments of the various elements, it is to be understood that other similar embodiments may be used or modifications and additions may be made to the presently described embodiment for performing the same function of the present invention without deviating therefrom. Therefore, the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with the recitation of the appended claims.