Patent Publication Number: US-2021172138-A1

Title: Floating flap gate apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a floating flap gate apparatus for preventing an influx of a rising water, and in particular, the present invention relates to a floating flap gate apparatus that makes it possible to effectively prevent an influx of water when a corner portion is present. 
     BACKGROUND ART 
     A floating flap gate exists which blocks an opening to a living space or an underground space at the time of a rising water in order to prevent the rising water from flowing into the living space or the underground space, by causing a door body to float, using a buoyancy of the water which is trying to flow in (e.g., Patent References 1 and 2). 
     The floating flap gates disclosed in Patent Reference 1 and Patent Reference 2 have a door body opening and closing auxiliary mechanism, and thus, the floating action of a door body is delayed at an initial stage of water influx, so the water does not flow into a living space or into an underground space, and it does not become difficult to lower the door body even when a water level is low, and the door body also does not suddenly fall. 
     The door body opening and closing auxiliary mechanism disclosed in Patent Reference 1 and Patent Reference 2 is constructed with a rope having a counterweight attached to a forward end of a door body, and with the other end attached to a counterweight or spring via a pulley, with the pulley installed so that the counterweight reaches its lowest point or the spring reaches its free length while the door body is rising or descending. 
     In Patent Reference 1, the auxiliary opening and closing mechanism of the door body is provided inside a stopper disposed on an inner side of a lowered door body. In Patent Reference 2, the auxiliary mechanism of the door body is provided inside a housing disposed in a position relative to a place where the rope is attached on both sides of a forward end surface of the door body. 
     That is to say, the auxiliary opening and closing mechanism assists in opening and closing the door body from both side portions of the door body. Therefore, when the width (span) of the door body increases, it becomes difficult to assist in opening the door body, so a limit was placed on the span of the door body. 
     Because of the above, there is a need to provide a land-based structure such as a stopper or a housing in a width-wise central portion of the door body when the span of the door body increases in cases where the auxiliary opening and closing mechanism of the door body disclosed in Patent Reference 1 or Patent Reference 2 is employed. 
     However, in cases where the auxiliary opening and closing mechanism of the door body disclosed in Patent Reference 1 and Patent Reference 2 is employed, it is impossible to install a land-based structure in a width-wise central portion of the door body. Also, the auxiliary opening and closing mechanism of Patent Reference 1 and Patent Reference 2 cannot provide a solution in an application in which it is not desirable to install a land-based structure in such a width-wise central portion of the door body. 
     Moreover, there are also cases in which parts of the above floating flap gate that prevent an influx of water has not only a rectilinear region, but also a corner portion. In cases where such a corner portion is present, a stopper is provided that corresponds to the corner portion, making it impossible to form a water-impervious wall continuous with the corner portion, thus making it impossible to effectively block the corner portion from an influx of water. 
     PRIOR ART REFERENCES 
     Patent References 
     Patent Reference 1: Japanese Patent Application Kokai Publication No. 2012-241449 
     Patent Reference 2: Japanese Patent Application Kokai Publication No. 2014-118774 
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     The problem that the present invention aims to solve is that in cases where a corner portion is present in an installation portion of a floating flap gate apparatus, it is impossible to form a water-impervious wall that is continuous with the corner portion, thus making it impossible to effectively block the corner portion from an influx of water. 
     The present invention was devised with the object of effectively blocking a corner portion present in an installation portion of a floating flap gate apparatus from an influx of water by forming a water-impervious wall that is continuous with the corner portion. 
     The present invention is a floating flap gate apparatus constructed to prevent an influx of a rising water, the floating flap gate comprising a door body configured such that a forward end of the door body swings upwards around a base end thereof within a plane in a height direction in a direction in which the water flows in, and having the following as its most essential features. 
     The floating flap gate apparatus according to the present invention comprises a floating flap gate arranged in a first rectilinear region, a floating flap gate arranged in a second rectilinear region, and a corner flap gate disposed in a corner portion where the first and second rectilinear regions intersect. 
     The corner flap gate has a plurality of door bodies divided by straight lines passing through a part of the corner portion where lines extending in a width-wise direction of a base end side bottom surface of the door bodies of the two floating flap gates intersect, and two adjacent ones of the plurality of door bodies are connected by a hinge structure that maintains a water-impervious state, and among the plurality of door bodies, a door body adjacent to a door body of the floating flap gates and the door body of the floating flap gate are connected by a hinge structure that maintains the respective water-impervious states. 
     According to the present invention configured as described above, the corner flap gate rises or lowers, following a raising or a lowering of the door bodies of the floating flap gates, thereby making it possible to effectively block the corner portion continuously. 
     In the present invention, the corner flap gate is formed on a base end side of the plurality of door bodies with a notched site that includes the part intersected by the corner portion, and if the notched site is covered with a water-impervious membrane that maintains a water-impervious state in the hinge structure, then it is possible to smoothly raise or lower each of the door bodies. 
     In the present invention, the angle of the corner portion may be 90° or more, or less than 90°, and the two floating flap gates are arranged in such a manner that a side surface of the second rectilinear region side of a door body of the floating flap gate arranged in the first rectilinear region in a lowered state, and a bottom surface of a gate body of a floating flap gate arranged in the second rectilinear region in a lowered state, are formed in a single straight line when viewed from above. 
     As long as there is a plurality of door bodies forming the corner flap gate in the present invention, the number thereof is not limited, but a configuration having three door bodies comprising a central door body, and a right-side door body and a left-side door body arranged on both sides of the central door body, is desirable from the standpoint of an ability to follow a raising or lowering of the door bodies of the floating flap gates. 
     According to the configuration described above, when the door bodies are lowered, the central door body, the right-side door body, and the left-side door body are flat; and when the door bodies are raised, the right-side door body and the left-side door body approach each other and fold into each other with respect to the central door body, making it possible to easily form a water-impervious wall continuous with the corner portion. When this happens, the interfolding of the central door body, the right-side door body, and the left-side door body makes it possible to absorb a difference of in a raising angle of the adjacent floating flap gate door bodies, even if different wave forces or wave directions operate on the adjacent floating flap gate door bodies, resulting in an occurrence of an instantaneous difference in water levels. 
     In the present invention, if a hinge structure is arranged on a surface side of the two floating flap gates and the corner flap gate in a lowered state, it is desirable, since there is no risk of an overflow of water flowing onto a top side of the hinge portion, as was the case when a hinge structure was attached to a back side. 
     Advantageous Effects of the Invention 
     According to the present invention, even in a case where a floating flap gate apparatus is installed at a location in which a corner portion is present, the corner flap gate raises or lowers, following a raising or a lowering of the door bodies of the floating flap gates, thereby making it possible to effectively block the corner portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1A through 1C  are schematic structural drawings of the first floating flap gate apparatus according to the present invention, where the angle of the corner portion is 90°.  FIG. 1A  is an elevated view of a lowered state.  FIG. 1B  is an elevated view of a raised state.  FIG. 1C  is a side view of a corner portion in a raised state. 
         FIGS. 2A through 2D  are drawings illustrating a hinge structure of a connecting part for the flap gate door bodies of the corner portion and the door bodies of the adjacent floating flap gates of the first floating flap gate apparatus according to the present invention.  FIG. 2A  is an elevated view.  FIG. 2B  is an enlarged view of part A in  FIG. 1A .  FIG. 2C  is an enlarged sectional view along the line B-B in  FIG. 2B .  FIG. 2D  is an enlarged sectional view along the line C-C in  FIG. 2B . 
         FIG. 3A  is an enlarged sectional view along the line E-E in  FIG. 2A . 
         FIG. 3B  is an enlarged sectional view along the line D-D in  FIG. 2A .  FIG. 3C  is an enlarged sectional view of part F in  FIG. 3B . 
         FIGS. 4A through 4C  are elevated views of a water-impervious structure of the first floating flap gate apparatus according to the present invention.  FIG. 4A  is a drawing illustrating a divided state of a door body of a corner flap gate.  FIG. 4B  is a drawing illustrating a water-impervious membrane provided to a floating flap gate and a corner flap gate.  FIG. 4C  is a drawing illustrating a presser plate of the water-impervious membrane. 
         FIGS. 5A through 5C  are drawings illustrating a raised state of a door body of the first floating flap gate apparatus according to the present invention when an instantaneous difference in water level occurs.  FIG. 5A  is an elevated view.  FIG. 5B  is a side view of a floating flap gate installed in the first rectilinear region.  FIG. 5C  is a side view of a floating flap gate installed in the second rectilinear region. 
         FIG. 6  is a drawing illustrating an interfolding auxiliary mechanism of a corner flap gate door body in the floating flap gate apparatus according to the present invention. 
         FIGS. 7A and 7B  are drawings illustrating a water pressure load support structure when a door body of a corner flap gate of the first floating flap gate apparatus according to the present invention in a lowered state.  FIG. 7A  is an elevated view.  FIG. 7B  is a side view of a floating flap gate installed in the second rectilinear region. 
         FIGS. 8A and 8B  are schematic structural drawings of a floating flap gate in a floating flap gate apparatus according to the present invention.  FIG. 8A  is a side view.  FIG. 8B  is a frontal view. 
         FIGS. 9A through 9D  are drawings illustrating various states of a storage area for a floating flap gate and a corner flap gate in a floating flap gate apparatus according to the present invention. 
         FIG. 10  is a drawing illustrating another example of a hinge structure of a connecting part for the left-side door body and the central door body of a corner flap gate in the first floating flap gate apparatus according to the present invention. 
         FIGS. 11A through 11E  are schematic drawings illustrating an example of deformation of the first floating flap gate apparatus according to the present invention in a lowered state as seen from above.  FIG. 11A  illustrates a case where the angle of the corner portion is less than 90°.  FIG. 11B  illustrates a case where the angle of the corner portion exceeds 90°.  FIG. 11C  illustrates a care where the width of the base end side of the central door body is at a minimum.  FIG. 11D  is an enlarged view of part G in  FIG. 11C .  FIG. 11E  illustrates an example of a case where the left-side door body and the central door body are equally divided. 
         FIGS. 12A and 12B  are schematic structural drawings of the second floating flap gate apparatus according to the present invention configured with a corner flap gate having two door bodies.  FIG. 12A  is an elevated view of a lowered state.  FIG. 12B  is an elevated view of a raised state. 
         FIG. 13  is an elevated schematic structural drawing of the third floating flap gate apparatus according to the present invention configured with a corner flap gate having four door bodies. 
     
    
    
     EMBODIMENTS 
     The present invention was devised with the object of forming a water-impervious wall that is continuous with a corner portion that is present in an installation portion of a floating flap gate apparatus, to effectively block the corner portion. 
     The above object is achieved by using a hinge structure that maintains a water-impervious state to connect (1) adjacent door bodies of a corner flap gate installed in a corner portion where a first rectilinear region where a floating flap gate is arranged intersects with a second rectilinear region, (2) a door body of a floating flap gate, and (3) a door body adjacent to these door bodies. 
     EXAMPLES 
     An embodiment of the present invention is described in detail, making use of  FIG. 1  to  FIG. 9 . Reference Numeral  1  is a floating flap gate apparatus according to the present invention installed at an end portion of a runway R, for example, in such a manner that a plurality of door bodies are disposed in a lowered state substantially in the same plane as the runway R. In an event of a tsunami, for example, the apparatus uses a pressure of a surging water w to swing a forward end side of a door body upwards using a base end side as a fulcrum, following the surging water w, to prevent the water w from flowing into the runway R. 
     In detail, the floating flap gate apparatus  1  of the present invention comprises floating flap gates  11  and  12  respectively arranged in a first rectilinear region S 1  on one side and in second rectilinear region S 2  on another side that intersect at an angle of 90°, for example, and a corner flap gate  21  installed in a corner portion C where the two rectilinear regions S 1  and S 2  intersect. 
     The floating flap gates  11  and  12  are, for example, installed in such a manner that each respective end portion of a bottom surface  13   f  of a base end side of a plurality of door bodies  13  approach or come into contact at a part that includes a point P where a line extending toward a width-wise direction of a bottom surface  13   f  of a base end side of the door bodies  13  that are connected in a width-wise direction intersects with the corner portion C. In this case, when viewed from above, a side surface  13   a  of the door body  13  of the floating flap gate  11  (or  12 ) installed at the first rectilinear region S 1  (or at the second rectilinear region S 2 ) in a lowered state forms a straight line with a side surface  13   f  of the door body  13  of the floating flap gate  12  (or  11 ) installed at the second rectilinear region S 2  (or at the first rectilinear region S 1 ) in a lowered state. 
     On the other hand, the corner flap gate  21  covers an interval between the adjacent door bodies  13  of the floating flap gates  11  and  12 . There are also provided three door bodies  22 : a central door body  23 , for example, that is divided by a straight line passing through the part that includes the point P of the corner portion C, as well as a right-side door body  24  and a left-side door body  25  arranged on both sides of the central door body  23 . 
     The part that includes the point P of the corner portion C includes not only the single point referred to as P, but also includes the vicinity of the point P. In an actual operation, in order to achieve a smooth upward swing of the door bodies  22 , some leeway is required when considering the manufacturing accuracy of the door bodies  22  and the hinge portion, because some deviation occurs regarding the point P that intersects at the corner portion C. 
     Among the three door bodies  22  of the corner flap gate  21 , the right-side door body  24  and the left-side door body  25  have a floating structure. Also, a side surface  24   b  on the floating flap gate  11  side of the right-side door body  24  and a side surface  25   b  on the floating flap gate  12  side of the right-side door body  25  are connected to a side surface  13   a  of the adjacent door bodies  13  of the floating flap gates  11  and  12 , by means of a hinge structure  31  that maintains each of them in a water-impervious state. 
     The hinge structure  31  is configured in a manner illustrated in  FIGS. 2B through 2D  and in  FIGS. 4B and 4C , for example. That is to say, in a case where a lowered state is viewed from a top surface side, the side surface  24   b  on the floating flap gate  11  side of the right-side door body  24  and the side surface  25   b  on the floating flap gate  12  side of the right-side door body  25  are connected to the side surface  13   a  of the adjacent door bodies  13  of the floating flap gates  11  and  12 , by forming interlocking parts that are caused to engage, with an interlocking engaging member  31   a  connected with a pin  31   b  that has a semicircular cross-section. Also, the top surface of the interlocking engaging member  31   a  that includes the pin  31   b  is pressed by a presser plate  31   d  on the corner flap gate  21  side via a water-impervious membrane  31   c  that serves as a hinge membrane and by a presser plate  31   e  on the floating flap gate  11 ,  12  side, thereby making it possible to stop water and to rotate. Reference Numeral  31   f  is a bushing that supports a free rotation of the pin  31   b , and Reference Numeral  31   g  is a bolt for attaching the presser plates  31   d  and  31   e.    
     Among the door bodies  22  of the corner flap gate  21 , the right-side door body  24  and the central door body  23 , and the central door body  23  and the left-side door body  25  are respectively connected by the hinge structure  32  that maintains each of them in a water-impervious state. 
     The hinge structure  32  is configured in a manner illustrated in  FIGS. 3A through 3C  and in  FIGS. 4B and 4C , for example. That is to say, on a top surface side of the door bodies  22  in a lowered state, there is provided a rubber membrane  32   a  that serves as an elastic membrane seal that covers adjacent side surfaces  24   a  and  23   a  of the right-side door body  24  and the central door body  23 , as well as adjacent side surfaces  23   b  and  25   a  of the central door body  23  and the left-side door body  25 . The rubber membrane  32   a  has a sufficient tensile strength to withstand a load when a water pressure is applied, and is covered with a strong fiber membrane  32   b  having outstanding weather-resistant properties, to form a hinge membrane  32   g . The rubber membrane  32   a  and the fiber membrane  32   b  are pressed by a presser plate  32   c  on the right-side door body  24  side, by a presser plate  32   d  on the central door body  23  side, and by a presser plate  32   e  on the left-side door body  25  side. When configured in this manner, it is possible to stop water and to rotate. Reference Numeral  32   f  is a rod for preventing the fiber membrane  32   b  from coming loose, and Reference Numeral  32   g  is a bolt for attaching the presser plate  32   e.    
     As shown in  FIG. 4A , the door bodies  22  of the corner flap gate  21  have a notched base end side that includes the point P intersecting at a corner portion C. As shown in  FIG. 4B , this notched site is covered by the water-impervious membranes  31   c  and  32   g  to maintain a water-impervious state in the hinge structures  31  and  32 . 
     In the event that a tsunami surges, for example, according to the corner flap gate  21  constructed as above, the door bodies  13  of the floating flap gates  11  and  12  installed at the two rectilinear regions S 1  and S 2  rise from the lowered state shown in  FIG. 1A . When this happens, the door bodies  22  of the corner flap gate  21  also rise, as shown in  FIGS. 1B and 1C , following the rising of the door bodies  13  of the floating flap gates  11  and  12 . 
     Use of the floating flap gate apparatus  1  according to the present invention makes it possible to form a water-impervious wall continuous with the corner portion C, due to the fact that the floating flap gates  11  and  12  are connected by the corner flap gate  21  in the manner described above. 
     In the case of the floating flap gates  11  and  12 , it is difficult to reach a maximum raising angle of 90° from a lowered state. This is because although the maximum raising angle is 90° if the floating flap gates  11  and  12  are by themselves, and do not include the corner flap gate  21 , but in the present invention, the corner flap gate  21  is included. The reason for this is that, according to the present invention, when the floating flap gates  11  and  12  rise to a raising angle of 90°, the end portions of the floating flap gates  11  and  12  approach each other, and there is no longer space for the folded corner flap gate  21 . Accordingly, the maximum raising angle is determined by devising an optimized design so as to make it possible to ensure that there is space for the folded corner flap gate  21 . A maximum raising angle of 75° is advantageous for the floating flap gates  11  and  12 . 
     The above example describes a case where the force exerted by the surging waves on the rectilinear region S 1  and on the rectilinear region S 2  are of the same magnitude. However, as shown in  FIG. 5 , for example, if the force of a surging wave exerted on the rectilinear region S 2  is greater than the force of a surging wave exerted on the rectilinear region S 1 , there results an instantaneous difference in water levels in the rectilinear regions S 1  and S 2 . Even in such a case, the corner flap gate  21  is able to absorb a difference in the raising angle of the door bodies  13  of the floating flap gates  11  and  12 . 
     Specifically, as shown in  FIG. 5 , when the door bodies  22  of the floating flap gate  21  are raised, the right-side door body  24  approaches and folds into the central door body  23  at a small raising angle, while the left-side door body  25  approaches and folds into the central door body  23  at a large raising angle. No matter what changes occur in the magnitude and direction of the waves surging onto the rectilinear region S 1  and the rectilinear region S 2 , the folding configurations of the right-side door body  24  and the left-side door body  25  adapt optimally to the central door body  23 , thereby making it possible to absorb a difference in the raising angle of the door bodies  13  of the floating flap gates  11  and  12 . 
     In order to achieve a smooth folding of the central door body  23 , the right-side door body  24 , and the left-side door body  25 , the adjacent side surfaces of the central door body  23  and the right-side door body  24 , as well as the adjacent side surfaces of the central door body  23  and the left-side door body  25 , may be formed as described below, for example. 
     As shown in  FIG. 4A , the central door body  23  forms a trapezoid wherein a width L 2  of a forward end side facing the forward end sides of the floating flap gates  11  and  12  is longer than a width L 1  of a base end side facing the base end sides of the floating flap gates  11  and  12 , while in a lowered state as viewed not only from the top surface side, but also from the back surface side at the bottom side of the paper in  FIG. 4A . Additionally, as shown in  FIGS. 3A and 3B , the central door body  23  forms an inverse trapezoid wherein a width L 4  of a back surface side is shorter than a width L 3  of a top surface side while in a lowered state. 
     On the other hand, with regard to the side surfaces  24   a  and  25   a  of the right-side door body  24  and the left-side door body  25  that face the side surfaces  23   a  and  23   b  that form the legs of the inverse trapezoid of the central door body  23 , a width L 6  of a portion parallel to the top surface side of the back surface side is shorter than a width L 5  of the top surface side of the right-side door body  24  and the left-side door body  25  in a lowered state, and as the rate whereby the width becomes shorter increases, the base end side gradually becomes greater than the forward end side, so as to become disposed diagonally. 
     In addition, if an auxiliary force generator  33  is installed at the door body  13  adjacent to the side surface  24   b  of the right-side door body  24  of the corner flap gate  21  and at the side surface  25   b  of the left-side door body  24 , in order to provide an auxiliary force in the folding direction of the right side door body  24  and the left-side door body  25 , it becomes possible to smoothly perform folding of the right-side door body  24  and the left-side door body  25  at the initial stage of raising the corner flap gate  21 . 
     There are no particular restrictions on the configuration of the auxiliary force generator  33 , but according to the example illustrated in  FIG. 6 , there is provided to the door body  13  of the floating flap gates  11  and  12  a push rod  33   b  projecting toward the side surface  24   b  of the right-side door body  24  or the side surface  25   b  of the left-side door body  25  of the corner flap gate  21  by means of a coil spring  33   a . In this case, when the door body is being lowered, the coil spring  33   a  compresses and the push rod  33   b  presses against the side surface  24   b  of the right-side door body  24  or the side surface  25   b  of the left-side door body  25  of the corner flap gate  21 , while being located inside of the door body  13  of the floating flap gates  11  and  12 . Then, when the door body starts to rise, a compression of the coil spring  33   a  is released, projecting the push rod  33   b , thereby pushing the right-side door body  24  and the left-side door body  25  in the folding direction thereof. 
     Although there are no particular restrictions on the installation location of the auxiliary generator  33 , it is more effective to install it at the forward end side of the door body  13 . There may be one or more than one of the auxiliary force generator  33 . If multiple auxiliary force generators are installed at a single door body  13 , each respective spring force of the coil spring  33   a  may be varied, or the spring force may be uniform and without variation. 
     In the case of the floating flap gate apparatus  1  having the above configuration according to the present invention, when the door bodies  13  and  22  rise, the water pressure load operating on the door bodies  22  of the corner flap gate  21  is transmitted via the hinge structures  32  and  31  to the floating flap gates  11  and  12  on both sides. In addition, the floating flap gates  11  and  12  are supported by tension rods  14  and by a bottom support member that bolsters the floating flap gates  11  and  12  (see  FIG. 7 ). 
     In the present invention, there are no particular restrictions on the construction of the floating flap gates  11  and  12  installed in the rectilinear regions S 1  and S 2 . However, it is advantageous to select a structure such as that shown in  FIG. 8 , in the case of a site where it is typically impossible to build a bulky structure such as a building or underground space with a wide opening, or a lock gate or an end portion of the runway R, or a site where one wishes to limit a height of a bulky structure such as a dike or a levee that would block a scenic view. 
     In further detail, in the floating flap gates  11  and  12  illustrated in  FIG. 8 , one end of a wire rope  41  is attached to a back side  13   b  of the door body  13  in a lowered state. The wire rope  41  is arranged such that a bracket  13   c  is attached to a center portion in a height direction of the door body  13  on the back side  13   b  of the door body  13 , for example, so that one end of the wire rope  41  is attached to the bracket  13   c . The other end of the wire rope  41  is retracted into an underground space  42   a  formed in a storage space  42  for the door body  13  in a position facing the bracket  13   c  at the forward end side of the door body  13 . 
     Within the underground space  42   a  are installed a counterweight  43 , a compression spring  44  provided on both sides of the upper surface of the counterweight  43 , and a group of connected pulleys that includes two fixed pulleys  45   a  and  45   b , and two movable pulleys  46   a  and  46   b . The other end of the retracted wire rope  41  is guided by the group of pulleys to an upper end of the counterweight  43 . The counterweight  43 , which has a width slightly smaller than that of the door body  13 , hangs downward due to being affixed to a ceiling portion of the underground space  42   a  in this position. 
     Among the group of pulleys, the first fixed pulley  45   a  is disposed at the retracted portion of the wire rope  41  in the underground space  42   a , while the second fixed pulley  45   b  is disposed at the ceiling portion of the underground space  42   a  which is the upper hanging position of the counterweight  43 . 
     On the other hand, the first movable pulley  46   a  is rotatably attached to at a lower end of a push-up rod  47  that moves vertically between the first fixed pulley  45   a  and the second fixed pulley  45   b . The second movable pulley  46   b  is attached to the counterweight  43 . 
     When the push-up rod  47  moves vertically, motion toward a forward end side  13   a  and a base end side  13   e  of the door body  13  in a lowered state is restricted by upper and lower guide rollers  47   a  and  47   b . Moreover, movement of the door body  13  in a lateral direction is restricted by upper and lower side rollers  47   c  and  47   d . In addition, the vertical rising and falling movement of the push-up rod  47  is restricted by an upper-limit stopper  47   e  and a lower-limit stopper  47   f , and a push-up roller  47   g  is attached at the upper end. 
     When raising the door bodies  13  and  22 , and when lowering the gates bodies  13  and  22 , the floating flap gates  11  and  12  and the corner flap gate  21  having an auxiliary mechanism for opening and closing the door bodies  13  that includes the first and second fixed pulleys  45   a  and  45   b , the first and second movable pulleys  46   a  and  46   b , the counterweight  43 , and the push-up rod  47  operate as described below. 
     When Raising the Door Bodies  13  and  22 : 
     When a water infiltration reaches a predetermined level, and a buoyancy operating on the door bodies  13  and a rotational force in the direction of raising resulting from an upward-pushing force of the push-up rod  47  exerted by the counterweight exceed the rotational force in the direction of lowering due to the weight of the door bodies  13 , the door bodies  22  start to float when the door bodies  13  start to float. 
     After the push-up rod  47  reaches its raising limit, the rotational force in the direction of raising resulting from water pressure operating on the immersed portions of the back surfaces  13   b  of the door bodies  13  exceeds the rotational force in the direction of lowering due to tension generated in the wire rope  41  caused by the weight of the door bodies  13  and the counterweight  43 . This results in the door bodies  13  rotating and rising in the direction of raising. The door bodies  22  also rise together with the rising of the door bodies  13 . 
     When the door bodies  13  rise to their raising limit, the counterweight  43  moves to the vicinity of its raising limit, and the compression spring  44  is compressed. Consequently, the tension of the wire rope  41  caused by the weight of the counterweight  43  and the compressive force of the compression spring  44  operates in the direction of lowering as a braking force on rotation of the door bodies  13  in the direction of raising. 
     When Lowering the Door Bodies  13  and  22 : 
     When there is a decrease in the rotational force in the raising direction resulting from water pressure operating on the immersed portions of the back surfaces  13   b  of the door bodies  13 , the door bodies  13  rotate in the direction of lowering up to a position where there is an equilibrium with the rotational force in the direction of lowering due to tension generated in the wire rope  41  caused by the weight of the door bodies  13  and the counterweight  43 . The door bodies also start to rise together with the rising of the door bodies  13 . In the vicinity of the upper limit of raising, the compressive spring force adds to the tension generated in the wire rope  41 . 
     While the rotational force in the lowering direction resulting from tension generated on the wire rope  41  by the weight of the door bodies  13  and the counterweight  43  and the rotational force in the direction of raising resulting from water pressure operating on the immersed portions of the back surfaces  13   b  of the door bodies  13 , the door bodies  13  rotate in the direction of lowering. The rotational force in the direction of lowering increases due to the weight of the door bodies  13 , but after the push-up rod  47  makes contact with the back surfaces  13   b  of the door bodies  13 , the lowering action decelerates due to the rotational force in the direction of raising resulting from the upward-pushing force of the push-up rod  47 . The door bodies  22  also lower together with the lowering of the door bodies  13 . 
     When there is no longer a buoyancy caused by water pressure operating on the immersed portions of the back surfaces  13   b  of the door bodies  13 , the door bodies  13  and  22  are inserted into the storage space  42 . When this happens, the upward-pushing force of the push-up rod  47  due to the counterweight  43  eases its impact during the insertion due to the upward-pushing force of the push-rod  47 , even though there is no rotational force in the direction of raising that is superior to the rotational force in the direction of lowering caused by the weight of the door bodies  13 . 
     In cases where it is typically impossible to build a bulky structure such as an end portion of the runway R, storage of the floating flap gates  11  and  12  and the corner flap gates  21  is accomplished in a boundary area between the land and water as illustrated in  FIG. 9A , or in a recessed area disposed in a land area adjacent to the water and formed in the same plane as the land area as illustrated in  FIG. 9B . 
     On the other hand, in cases where a bulky structure such as a dike does not disturb the view, storage is accomplished in a boundary area between the land and water as illustrated in  FIG. 9C , or on a top surface of the land adjacent to the water as illustrated in  FIG. 9D . 
     The present invention is not limited to the above-described example, and the preferred embodiment may, of course, be advantageously modified within the scope of the technical ideas recited in the claims. 
     For example, according to the above example, in the corner flap gate  21 , the hinge structure  32  has a double structure, with a rubber membrane  32   a , and a fiber membrane  32   b , serving to maintain a water-impervious state for the right-side door body  24  and the central door body  23 , and the central door body  23  and the left-side door body  25 , respectively (see  FIG. 3C ). 
     However, as shown in  FIG. 10 , a fiber-reinforced rubber  32   h  may be used as a rubber lining for a fiber material possessing tensile strength to maintain water-imperviousness. 
     The above example describes a case where an angle θ of the corner portion C is 90°. However, as shown in  FIG. 11A , the angle θ of the corner portion C may be less than 90°. Conversely, as shown in  FIG. 11B , the angle θ of the corner portion C may exceed 90°. 
     Additionally, in the above example, because raising of the right-side door body  24  and the left side door body  25  are made easier due to the buoyancy or the auxiliary force generator  33 , the right-side door body  24  and the left-side door body  25  were made as large as possible, and the central door body  23  was made as small as possible. In this case, the minimum value for the width L 1  of the base end side of the central door body  23  is a width that enables attachment of the presser plate  32   d , as shown in  FIGS. 11C and 11D . However, as shown in  FIG. 11E , the central door body  23 , the right-side door body  24 , and the left-side door body  25  may be divided into equal angles with the point P at the center. 
     In the above example, the forward end surfaces of the central door body  23 , the right-side door body  24 , and the left-side door body  25  form straight lines when in a lowered state when viewed from above. However, as shown in  FIG. 11C , the forward end surfaces of the central door body  23 , the right-side door body  24 , and the left-side door body  25  may form convex curves. 
     Moreover, in the above example, the door bodies  22  of the corner flap gate  21  are formed from three gate bodies: the central door body  23 , the right-side door body  24 , and the left-side door body  25 . However, the number of door bodies forming the door bodies  22  may be two, as shown in  FIG. 12 . If the door bodies can be raised when positioned in the central portion and dependent on a buoyancy alone, then the number of door bodies may be four, as shown in  FIG. 13 . 
     In the various types of examples described above, the height and thickness of the door bodies  13  of the two floating flap gates  11  and  12  are determined by devising an optimized design so as to make it possible for the door bodies  13  to rise and descend according to a known angle θ of the corner portion C. This likewise applies to the number, configuration, height, and thickness of the door bodies  22  of the corner flap gate  21 . 
     EXPLANATION OF THE REFERENCE NUMERALS 
     
         
         
           
               1  Floating flap gate apparatus 
               11 ,  12  Floating flap gates 
               13  Door body 
               13   a  Side surface 
               13   d  Forward end side 
               13   e  Base end side 
               13   f  Bottom surface 
               21  Corner flap gate 
               22  Door body 
               23  Central door body 
               24  Right-side door body 
               25  Left-side door body 
               31 ,  32  Hinge structures 
               33  Auxiliary force generator 
               41  Wire rope 
               42  Storage space 
               42   a  Underground space 
               43  Counterweight 
               45   a  First fixed pulley 
               45   b  Second fixed pulley 
               46   a  First movable pulley 
               46   b  Second movable pulley 
               47  Push-up rod 
             S 1  First rectilinear region 
             S 2  Second rectilinear region 
             C Corner portion 
             θ Angle of the corner portion