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RELATED APPLICATIONS 
       [0001]    This application claims the priority of Provisional Application Ser. No. 60/821,990 entitled Spillway Weir Gate, filed Aug. 10, 2006, the content of said application being incorporated herein by reference. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    A device for diverting flow from a canal drop, small earthen dam or branch to an emergency spillway should a primary diversion fail unexpectedly was required at a small hydroelectric project being developed by the inventors. Several commercial products were available, such as the Obermeir Hydro, Inc. Pneumatically Operated Spillway Gate. This gate consists of a hinged plate held in place by an air bladder. In order to operate, this product includes a control valve, which could fail to operate. In the interest of providing a gate with no controls, a simple, economical alternative was required. 
       SUMMARY OF THE INVENTION 
       [0003]    The present invention is directed to a device and method for directing or diverting a flow of water from a first water channel to an emergency spillway in the case of a spillover or other control event wherein water from a first water channel overflows. An automatic trip gate is installed in a gate support structure at a bank of an impounded body of water. The automatic trip gate controls a release of an overflow of water through the gate support structure upon the occurrence of an overflow event. The automatic trip gate includes a plate supported by a hinge assembly that attaches to the support structure. A trough attached to the plate catches and retains overflow water. When the level of overflow water in the trough reaches a tipping level, the plate pivots from a substantially vertical orientation wherein the impounded body of water is maintained behind the plate, to a tipped position wherein the impounded body of water is released through the gate support. In a preferred embodiment of the invention, a plunge pool is located below the automatic trip gate that absorbs the energy imparted by the plate when tripped. 
         [0004]    In one embodiment, the automatic trip gate is installed or constructed in feed canal at a hydroelectric plant. The flow and head for the plant was developed at an intersection of two earthen irrigation canals. The plant took flow from a branch that dropped 38 feet from the upper canal to a lower canal. Flow normally passes through the plant turbines. When the plant is shutdown, flow is bypassed through an existing flume by opening two small radial gates via an automated control system. In the event that the bypass failed the canal would be over topped, and possibly wash out. In the described embodiment and installation, a separate spillway fitted with multiple automatic trip gates provided the solution to this concern. 
         [0005]    The automatic trip gate and spillway of the present invention may be used at any impoundment, dam or canal where overtopping could cause failure of the structure due to erosion. In many cases, a lowered section in the dam acts as an emergency spillway and discharges into some form of channel. This, however, reduces head or storage behind the dam. With the automatic trip gate, the operating level can be higher, near the top of the gate, which will tip over and discharge into a channel when water level exceeds a set point. 
     
     
       DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is an overhead plan view of an automatic trip gate system according to the present invention. 
           [0007]      FIG. 2  is an isometric view of an automatic trip gate system according to the present invention. 
           [0008]      FIG. 3  is an isometric view of an automatic trip gate according to the present invention. 
           [0009]      FIG. 4  is a cross section of the automatic trip gate according to the present invention, showing upstream operating water level and the entrance to the spillway. 
           [0010]      FIG. 5  is a cross section of the automatic trip gate according to the present invention, showing a tripping water level. 
           [0011]      FIG. 6  is a cross section of the automatic trip gate according to the present invention, showing a post tripping water level. 
           [0012]      FIG. 7  is a detailed part plan showing a seal for one side of the automatic trip gate. 
           [0013]      FIG. 8  is an overhead plan view showing an installation of a single automatic trip gate. 
           [0014]      FIG. 9  is a detailed side view of the bottom seal of the automatic trip gate. 
           [0015]      FIG. 10  is an overhead plan view of an automatic trip gate according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]      FIG. 1  a typical installation of automatic trip gate system  50  including in this installation three separate automatic trip gates  20 A,  20 B and  20 C. In the instance represented in  FIG. 1 , automatic trip gate system  50  is installed at a location on canal C, where a low head hydroelectric plant, (not shown), has been established. Intake structure IS provides a flow of water to the hydro-electric plant during generation. When the hydroelectric plant experiences an unexpected shut down, overflow of canal water is handled by automated bypass AB, which is controlled in conjunction with the control of operation of the hydroelectric plant such that while water is flowing through the intake structure IS to the turbine, (not shown), located in the hydroelectric plant, a controlled valve, (not shown), of the automated bypass AB is closed so that flow is diverted through the intake structure IS. When the hydro-electric plant is out of service or operation, the controlled valve of the automated bypass AB is opened so that flow is diverted to a stilling basin or canal, (not shown). 
         [0017]    In the event that the hydro-electric plant experiences an unexpected shut down, i.e. no water flow is being diverted through the turbine, and the controlled valve of the automated bypass AB is inoperative and fails to open for any of a number of reasons, flow, in an overtopping situation, will be diverted by operation of the automatic trip gate system  50  to a stilling basin or canal through outlet pipe  46 . 
         [0018]      FIGS. 1 and 2  show automatic trip gate system  50  is installed in a trip gate support structure, in this case spillway  40  which is constructed at a bank B of an impoundment of water W, in this case canal C. Each of the three separate automatic trip gates  20 A,  20 B and  20 C are installed between support structures of the spillway  40 . Automatic trip gate  20 A is installed between spillway sidewall  41 A and first pier  42 A. Similarly, automatic trip gate  20 B is installed between first and second piers  42 A and  42 B. Automatic trip gate  20 C is installed between spillway sidewall  41 B and second pier  42 B. 
         [0019]    As shown in  FIG. 2 , each of the automatic trip gates  20 A,  20 B and  20 C include a trough  21 A,  21 B and  21 C respectively. Spillway  40  is also constructed such that below each of the three separate automatic trip gates  20 A,  20 B and  20 C, a plunge pool is located. Thus plunge pool  45 A is formed below automatic trip gate  20 A, plunge pool  45 B is formed below automatic trip gate  20 B and plunge pool  45 C is formed below automatic trip gate  20 C. Each plunge pool  45 A,  45 B and  45 C is formed behind a retaining wall  43 A,  43 B and  43 C respectively. 
         [0020]    Referring to  FIGS. 3 ,  4 ,  5  and  6  automatic trip gate  20 A is shown supported by gate support structure  47  and installed against spillway sidewall  41 A. Plunge pool  45 A is shown formed below automatic trip gate  20 A and behind retaining wall  43 A. Automatic trip gate  20 A is shown including trough  21 A attached to plate  35  by gate top plate  22 . The top of the trough  21 A is covered by trash screen  27  which prevents trash and other debris from filling trough  21 A. Automatic trip gate  20 A is pivotably supported by hinged support arm assembly  30 . Hinged support arm assembly  30  is typical of the plurality of hinged support arm assemblies that pivotably support trough  21 A. 
         [0021]    Referring to  FIGS. 4 ,  5  and  6 , hinged support arm assembly  30  includes foot  31  that extends between and is connected at one end to plate  35  and at a second end to hinge end support  34  by hinge pin  32 . Hinge end support  33  attaches to gate support structure  47  using hardware  36 . Hinge pin  32  is supported in hinge end support  34  by bushing  33 . In a preferred embodiment, bushing  33  is a nylon, molybdenum impregnated self-lubricating which provides low friction for the overturning action. Also in a preferred embodiment, foot  31  is welded to plate  35 . 
         [0022]      FIGS. 4 ,  5  and  6  show automatic trip gate  20 A as it goes from standby position wherein water W retained behind automatic trip gate  20 A is maintained at a desired operating level L 1  as shown in  FIG. 4 , to tipped position as seen in  FIG. 6 , wherein automatic trip gate  20 A is shown in a tripped position and water W is maintained at a post-trip level L 3 . 
         [0023]      FIG. 5  shows water W behind automatic trip gate  20 A has reached an overflow level L 2 , wherein water W has crested plate  35 , and begins to flow over trip gate top plate  22  filling trough  21 A. In  FIG. 5 , trough  21 A is shown retaining overflow water OF which, when it reaches a tripping level TL, causes trough  21 A and the attached trip gate top plate  22  and plate  35  to pivot at the axis of rotation A of hinge pin  32  along trip path P releasing water W through spillway  40 . 
         [0024]    Referring to  FIGS. 4 and 5  it will be noted that a plunge water level PL is controlled in plunge pool  45 A. At a desired operating level L 1  some splash will invariably come over the top of plate  35 , flowing over trip gate top plate  22  filling trough  21 A. Drain hole  23  in trough  21 A drains water from trough  21 A that has entered by casual wave action or precipitation so that the level of overflow water OF does not reach tripping level TL when an overflow event has not occurred. The speed at which overflow water OF drains from trough  21 A, and therefore also the speed at which the level of overflow water OF rises and reaches tripping level TL, can be regulated by the size and number of drain holes  23  incorporated in trough  21 A. Troughs  21 A,  21 B and  21 C may be constructed in such a manner that they reach a trip level substantially at the same time or in a sequence. 
         [0025]    As the level of water W in canal C rises, more water W begins to come over plate  35  and trip gate top plate  22  filling trough  21 A. When the water level in trough  21 A reaches tripping level TL, plate  35  and the attached trip gate top plate  22  and trough  21 A tip rotating at the axis of rotation A of hinge pin  32  along path P. Plunge water level PL in plunge pool  45 A is high enough that the water contained in plunge pool  45 A acts to absorb the energy imparted by the plate  35  and the attached trip gate top plate  22  and trough  21 A. Plunge water level PL may be filled initially by diverting water from canal C, i.e. through a hose or other conduit, not shown. Alternately plunge water level PL is filled following a tripping of plate  35 . Plunge water level PL is maintained by precipitation or minor leakage around the seals. Excess plunge water level PL flows over the top of wall  43 A. Plunge pool  45 A may be drained by opening drain valve  44 . 
         [0026]    Flow over the tripped automatic trip gate  20 A determines the length and height of automatic trip gate  20 A using the formula Q=KLH 3/2, using a K factor of 3.33 for a flat, broad-crested weir. The length of automatic trip gate  20 A can be selected first and the height can be calculated using the above formula. The converse is true, the height of automatic trip gate  20 A can be selected and the length is then a function of the formula. Referring to  FIG. 5 , a desired water level L 1  is held approximately 7.62 centimeters, (three inches), below the top of plate  35 . This level can be selected based on the top of the canal or dam embankment. For example, the top of the embankment  48  can be approximately 22.86 centimeters, (nine inches), above the desired operating level L 1  to provide a safety factor for waves or other brief disturbances. 
         [0027]    Plate  35  is made of a thick steel plate. Trough  21 A and trip gate top plate  22  are made of a thin steel plate. The weight of plate  35  and the length of foot  31  extending between plate  35  and hinge pin  32  provide the moment to resist the opposite hydraulic force from water W. A seen in  FIG. 4 , trough  21 A is located at lest partially behind or downstream from an axis of rotation A of hinge pin  32  so that as trough  21 A fills, it adds overturning moment. 
         [0028]      FIG. 7  shows details of lower gate seal  26  which is of the solid bulb and tail seal type, as manufactured by Seals Unlimited of Beaverton, Oreg. Lower gate seal  26  is held in place by steel support angle  28  and pinch bar  29 . A compressive force is maintained between steel support bar  28  and pinch bar  29  by a plurality of screws  27 . 
         [0029]      FIG. 8  is an overhead plan view showing an installation of a single automatic trip gate  120  installed between side structure  141  and  142  of spillway  140 . Automatic trip gate  120  is shown including trough  121  attached to plate  135  by gate top plate  122 . The top of trough  121  is covered by trash screen  127  which prevents trash and other debris from filling trough  121 . Trough  121  includes a plurality of drain holes  123  which regulate a water level maintained in trough  121 . Plunge pool  145  is shown formed below automatic trip gate  120  and behind retaining wall  143 . Automatic trip gate  120  is shown including lower gate seal  126  and lateral gate seal  125  respectively. Lateral gate seal  125  is typical of the lateral gate seals installed at either side of plate  135 . Plate  135  is manufactured having a clearance at either side with respect to side structure. For instance in one embodiment, a width of plate  135  is approximately 1.27 centimeters, (½ inch), less than a distance between side structure giving approximately 0.64 centimeters, (¼ inch), clearance on each side to prevent interference with side structure  141  and  142 . 
         [0030]      FIG. 9  shows details of lateral gate seal  125  comprises solid bulb and tail seal  123 , as manufactured by Seals Unlimited of Beaverton, Oreg. Lateral gate seal  125  is typical of the seal fitted to both sides of plate  135 . Lateral gate seal  125  is held in position by steel support angle  126  and pinch bar  29 . A compressive force is maintained between steel support bar  124  and pinch bar  123  by a plurality of screws  126 . 
         [0031]      FIG. 10  shows automatic trip gate  220  including trough  221  attached to plate  235  by gate top plate  222 . Automatic trip gate  220  is fabricated with integrated trip gate support structure, namely side plates  241  and  242 . Side plates  241  and  242  not only provide integrated support for hinged support arm assembly  230  and the pivotally attached plate  235  and trough  221 , but the side plates  241  and  242  also provide a smooth, flat surface that promotes the life of seals, (not shown in  FIG. 10 . Side plates  241  and  242  also reduce if not eliminate the incidence of jamming during tipping. The top of trough  221  is covered by trash screen  227 . Automatic trip gate  220  is pivotably supported by hinged support arm assembly  230 . Hinged support arm assembly  230  is typical of the plurality of hinged support arm assemblies that pivotably support trough  221 . 
         [0032]    The foregoing description of the illustrated embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or to exemplary embodiment(s) and implementation(s) disclosed. Numerous modifications and variations will be apparent to practitioners skilled in this art. Process steps described might be interchangeable with other steps in order to achieve the same result. At least one preferred embodiment was chosen and described in order to best explain the principles of the invention and a best mode of practical application, thereby to enable others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use or implementation contemplated. It is intended that the scope of the invention be defined by the claims appended hereto and their equivalents. Reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather means “one or more.” Moreover, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the following claims. No claim element herein is to be construed under the provisions of 35 U.S.C. Sec. 112, sixth paragraph unless the element is expressly recited using the phrase “means for . . . ”

Summary:
An automatic trip gate for installation in a gate support structure at a bank of an impounded body of water. The automatic trip gate controls a release of an overflow of water through the gate support structure upon the occurrence of an overflow event. The automatic trip gate includes a plate supported by a hinge assembly that attaches to the support structure. A trough attached to the plate catches and retains overflow water. When the level of overflow water in the trough reaches a tipping level, the plate pivots from a substantially vertical orientation wherein the impounded body of water is maintained behind the plate, to a tipped position wherein the impounded body of water is released o through the gate support. A plunge pool is located below the automatic trip gate that absorbs the energy imparted by the plate when tripped.