Abstract:
A barrier for reducing erosion along shorelines includes a barrier body formed as a unitary, molded plastic structure. In one embodiment, the barrier body has at least one elongate passage extending through it, between oppositely disposed first and second sides, and an interior reservoir. A port formed into the barrier body communicates with the interior reservoir to facilitate filling the reservoir with material to thereby add weight to the barrier. The barrier further includes at least one anchor formed into a side of the barrier body and associated with the passage to control shrinkage of the barrier body as it is being molded. In another embodiment, a method of making the barrier body includes placing plastic material in a mold, manipulating the mold to distribute the plastic material within the mold and thereby form the barrier body as a unitary piece, and reducing the shrinkage of the molded barrier body with the anchor.

Description:
CROSS REFERENCE 
   This application is a continuation of U.S. patent application Ser. No. 10/997,226, filed Nov. 24, 2004, now abandoned. 

   FIELD OF THE INVENTION 
   The present invention relates generally to a device for reducing erosion along shorelines. 
   BACKGROUND OF THE INVENTION 
   The erosion of shorelines as a consequence of wave action is a well-known phenomenon. Generally, erosion is a function of persistent wave action exerted on beaches comprising sand or fine-shingled material and is most frequently encountered along shorelines of large bodies of water where such wave action can be generated. As a consequence of this persistent wave action, material on the shore tends to be loosened and the continuous reciprocating movement along the shoreline causes such materials to generally erode. The problems of erosion are emphasized along exceptionally long shorelines where the phenomena of littoral drift is enhanced. In those situations, devices such as breakwaters and revetments tend to increase downstream erosion. 
   In an attempt to combat shoreline erosion, many municipalities have resorted to dredging sand from outlying portions of the body of water and depositing the sand on the beach. The dredging process is generally very expensive and serves only as a temporary solution to the problem as the shore is gradually and continually eroded. Moreover, dredging sand from the floor beneath the body of water creates other environmental concerns such as damage to marine life which inhabit the sea floor. 
   Other devices for controlling erosion along shorelines have been proposed in the form of barriers positioned along the shoreline, or at a distance in the water spaced from the shoreline, to dissipate wave action. However, many of these devices do not aid in building beach behind the barrier structures, and some actually cause increased erosion in front of the barrier structures. To address this problem, some devices have been configured to facilitate the deposition of sand on the beach behind the barrier structures. A large majority of these devices are formed from concrete material and are therefore susceptible to wear and erosion by the natural wave action they are intended to combat. Accordingly, these structures usually become cracked, eroded, or otherwise damaged over the course of time. 
   U.S. Pat. No. 4,129,006 to Payne is directed to an erosion control system which, in one embodiment, comprises modular, hollow units. The hollow units may be filled with water to add sufficient weight to moor the system on the beach. Several of the modular units are coupled together with tie rods to form a barrier structure for combating erosion. 
   Accordingly, despite the various proposed devices and methods for controlling erosion along shorelines, no one method or device has been widely accepted, and the control of erosion along shorelines continues to be a topic of intensive research. A need therefore exists for an erosion control barrier which addresses these and other drawbacks of the prior art. 
   SUMMARY OF THE INVENTION 
   The present invention provides a barrier for controlling erosion along shorelines. Each barrier is a modular unit that can be arranged together with several other such barriers to form a barrier wall along a shoreline. In one embodiment, the barrier comprises a unitary, molded plastic body with opposing first and second sides and an interior reservoir. At least one elongate passage extends through the barrier body between the first and second sides to permit water to flow through the barrier, from a seaward facing side to a landward facing side. At least one anchor formed into the second side of the barrier is associated with the elongate passage. The anchor controls shrinkage of the molded barrier body during manufacture of the barrier. The barrier further includes a port formed into the barrier body and communicating with the interior reservoir to facilitate filling the reservoir with concrete, sand, water, stones, or other material. 
   In another embodiment, the elongate passage includes first and second apertures formed on the first and second sides of the barrier, respectively. The apertures are sized such that the second aperture is smaller than the first aperture, and the elongate passage is tapered along its length between the first and second apertures. When the barrier is oriented with the first side facing seaward, water is forced through the passage by wave action and the tapered shape acts like a nozzle to increase the velocity of the water through the passage. As the water exits the second aperture on the second, landward facing side, it is propelled a distance behind the barrier. As the water flows back toward the shore, it is impeded by the barrier so that any sand that is mixed with the water settles out to build the beach behind the barrier. While water can flow through the passage back toward the shore, the smaller aperture on the second side helps to slow the flow and thereby facilitate settling sand out of the water. 
   In another embodiment of the invention, a barrier according to the invention is formed in a rotational molding process. The mold used to form the barrier includes a cavity that defines the exterior shape of the barrier, at least one elongate core extending through the cavity, and an anchor affixed within the cavity proximate the core. The method includes placing thermoplastic material in the mold, heating the mold, manipulating the mold to distribute the thermoplastic material through the mold cavity and thereby form the unitary barrier, and reducing shrinkage of the molded barrier with the anchor. 
   The features and objectives of the present invention will become more readily apparent from the following Detailed Description taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the invention. 
       FIG. 1  is a perspective view of an exemplary erosion barrier according to the present invention; 
       FIG. 2  is a perspective view depicting several barriers of  FIG. 1  arranged in an interlocking manner; 
       FIG. 3  is a cross-sectional view of a barrier of  FIG. 2 , taken along line  3 — 3 ; 
       FIG. 4  is a top plan view of the barriers of  FIG. 2 ; 
       FIGS. 5A–5D  are schematic, cross-sectional views depicting a molding process for manufacturing the barrier of  FIG. 1 ; 
       FIG. 6  is a rear elevation view of the barrier of  FIG. 1 . 
       FIG. 7  is a cross-sectional view similar to  FIG. 3 , depicting another embodiment of an erosion barrier according to the present invention; and 
       FIG. 8  is a rear elevation view, similar to  FIG. 6 , depicting several barriers arranged end-to-end. 
   

   DETAILED DESCRIPTION 
     FIG. 1  depicts an exemplary erosion control barrier  10 , according to the present invention. In this embodiment, the barrier has the general shape of a trapezoidal prism with substantially horizontal top and bottom walls  12 ,  14 , first and second opposing, inclined sidewalls  16 ,  18 , and first and second opposing end walls  20 ,  22 . The first and second sidewalls  16 ,  18  are inclined toward one another, from the bottom wall  14  toward the top wall  12 , to form the generally trapezoidal shape. While the first and second end walls  20 ,  22  are substantially vertically oriented, they are formed as convex and concave arcuate surfaces that extend between the first and second sidewalls  16 ,  18 , respectively. The convex and concave surfaces are complementary so that multiple barriers  10  may be aligned in an end-to-end fashion with their first and second end walls  20 ,  22  engaging one another to form a barrier wall  24 , as depicted in  FIGS. 2 ,  4  and  8 , and described more fully below. 
   A plurality of elongate passages  30  are formed through the barrier  10 , between the first and second sidewalls  16 ,  18 . Each passage  30  includes first and second apertures  32 ,  34  formed on the first, and second sidewalls  16 ,  18 , respectively, whereby fluid, such as seawater, may pass entirely through the passages  30  from the first side to the second side. In the embodiment shown, the passages are generally cylindrical in shape and the second apertures  34  are smaller than the first apertures  32 . The passages  30  are correspondingly tapered along their lengths from the first apertures  32  to the second apertures  34 . While the passages  30  and apertures  32 ,  34  are depicted herein as having generally circular cross sections or shapes, it will be recognized that the passages  30  and apertures  32 ,  34  may be formed in various other shapes, as may be desired, and the passages need not be tapered. As a non-limiting example,  FIGS. 7 and 8  depict another embodiment of a barrier  10   a  wherein the apertures  32   a ,  34   a  are substantially the same size and the passages  30   a  are not tapered, though they may formed with a slight draft to facilitate manufacture. The passages  30   a  and apertures  32   a ,  34   a  have generally rectangular cross sectional shapes, as best seen in  FIG. 8 . 
   When one or more barriers  10  are positioned along a shoreline, water and sand from waves  36  impacting the first, or seaward-facing sidewall  16  of the barrier  10  enter the first apertures  32  and are forced by the wave action through the passages  30  to exit from the second apertures  34  on the second, or landward-facing sidewall  18  of the barrier  10 , as depicted in  FIG. 3 . In the embodiments where the passages  30  are tapered, the passages  30  act as nozzles to increase the velocity of the water traveling through the passages  30  so that the water is ejected from the second apertures  34  and propelled a distance behind the second sidewall  18  of the barrier  10 . As the water flows back toward the shoreline, it is impeded by the barrier  10  so that sand which is intermixed with the water settles out and is deposited behind the second sidewall  18  of the barrier  10  whereby the beach is increased on the landward side of the barrier  10 . The relatively smaller size of the second apertures  34  formed on the second sidewall  18  of the barrier  10  further increases the beach building functionality of the barrier by impeding the flow of water back through the passages  30  and giving the sand additional time to settle out of the water. 
   By aligning multiple barriers  10  end-to-end along a stretch of shoreline, the barriers form a barrier wall  24  that dissipates wave action, and accretes the beach behind the barriers, as described above. The interlockinq connection provided by the respective arcuate first and second end walls  20 ,  22  helps adjacent barriers  10  resist movement under the force of impacting waves  36 . Moreover, the respective arcuate shapes facilitate offsetting consecutive barriers relative to one another, in an angular fashion, so that the barrier wall  24  can be arranged to follow the contour of the shoreline. 
   In one embodiment, the barrier  10  is formed as a unitary, molded, plastic, hollow barrier body  28  having an interior reservoir  40 , as depicted in  FIGS. 3 and 5D . The reservoir  40  may be filled with a material to increase the weight of the barrier and facilitate mooring the barrier  10  along a shoreline. Such fill materials include, but are not limited to, sand or other sedimentary material, water, small stones, or other material. In one embodiment, the barrier body  28  is filled with concrete material  42 . To facilitate filling the interior reservoir  40 , a port  44  may be formed into the top wall  12  of the barrier body for communication with the interior reservoir  40 . A second port or vent  46  may be formed in the top wall  12  to facilitate the evacuation of air from within the interior reservoir  40  as the fill material is being added. The port  44  and vent  46  may thereafter be capped with a cover  48 , or otherwise sealed, to retain the fill material within the interior reservoir  40 . In one embodiment, covers  48  over the port  44  and vent  46  are friction welded or spin welded to the top wall  12 . 
   The barrier  10  according to the present invention facilitates transportation and erection of a barrier wall  24 . Specifically, unfilled barrier bodies  28  may be easily transported to an erection site and positioned along a shoreline as desired. Thereafter, the individual barrier bodies  28  may be filled with a fill material, such as concrete, sand, water, small stones, or other material, to help moor the assembled barrier wall  24  in position. Because of the modular design of the individual barriers  10 , they may be repositioned to form a new barrier wall  24  along a different section of the beach after a period of time has passed and/or after sufficient accretion of beach behind the previous barrier wall  24  has been obtained. In this manner, the barriers  10  may be reused to facilitate increasing the beach area. 
   The barrier body  28  may be formed from polyethylene, polypropylene, vinyl, nylon, plastisol, or any other plastic material that is impervious to water and provides good wear resistance. In one embodiment, the barrier body  28  is formed from linear low-density polyethylene available, for example, from Exxon-Mobile Corporation. Although the dimensions of the barrier may vary, in one embodiment, a barrier  10  in accordance with the present invention has an overall height of about 36 inches, an overall length of about 60 inches, and an overall width of about 60 inches. 
   Referring now to  FIGS. 5A–5D , a method for manufacturing an erosion barrier  10  using a rotational molding process will now be described. In this embodiment, the rotational molding process forms the unitary molded plastic barrier body  28 . As depicted in  FIG. 5A , the rotational mold  50  comprises a mold shell  52  with an internal cavity  54  having surfaces that define the corresponding external surfaces of the molded barrier body  28 . The mold shell  52  will generally include one or more mold sections which may be separated to permit the molded barrier body  28  to be removed from the cavity  54 . In the embodiment shown, the mold  50  comprises at least upper and lower mold sections  56 ,  58 , but it will be recognized that the mold  50  may include other separable sections to facilitate molding the barrier body  28  and removing the barrier body  28  from the mold cavity  54 . In the embodiment shown, the upper and lower mold sections  56 ,  58  are secured together by clamps or hasps  57  with corresponding components  59   a ,  59   b  disposed on the upper and lower mold sections  56 ,  58 , respectively. 
   A plurality of tapered tubes  60  extend through the mold cavity  54 , between spaced opposing sides  62 ,  64 , to form the tapered passages  30  through the barrier body  28 . In this embodiment, the wide ends  66  of tubes  60  are fixed to the lower section  58  of the mold  50  and the narrower ends  68  of the tubes  60  extend through and sealingly engage corresponding apertures  69 ,  70  formed in the upper section  56  of the mold  50 . In the embodiment shown, the tubes  60  are formed from aluminum material and their exposed surfaces are covered with a Teflon® coating that resists adhesion of the formed plastic barrier body  28  and facilitates removal of the barrier body  28  from the mold  50 . 
   The upper section  56  of the mold  50  includes one or more core plugs  72  (only one shown) that define the port  44  and vent  46  formed into the top surface  12  of the barrier body  28 . The core plugs  72  are installed through apertures  71 ,  73  formed in the mold  50 . Teflon® tubes  74  extend through the wall of the mold  50  at the core plugs  72  and communicate with the mold cavity  54  via passages  76  to vent the cavity  54  during the rotational molding process. Because the tubes are formed from Teflon® material, the plastic material used to form the barrier body  28  will not adhere to the tube  74 . 
   To form the barrier body  28 , mold release agent is applied to the interior surfaces of the mold cavity  54  and to the tapered tubes  60  while the upper and lower mold sections  56 ,  58  are separated. The mold release agent may be any solid or water-based mold release agent. In one embodiment, the mold release agent is TraSys™ 420 available from DuPont of Wilmington, Del. Resin material  80  for forming the barrier body  28  is then added to the mold cavity  54  and the upper and lower sections  56 ,  58  are secured together to seal the mold cavity  54 . The closed mold  50  is then placed in a conventional rotational molding oven and is manipulated about at least two orthogonal axes to cause the resin material  80  to uniformly coat the interior surfaces of the mold  50  as the mold  50  is heated, as known in the art. As the interior surfaces of the mold  50  become hot, the resin material  80  melts and fuses together to form wall surfaces  90  that define the barrier body  28 . 
   To ensure that the passages  30  through the barrier body  28  are properly formed, pressurized, heated air from a heated air source  98  is forced through the tapered tubes  60  to facilitate heating the tubes. To accomplish this, the wide ends  66  of the tapered tubes  60  are closed off with caps  82  and heated air is forced through the tubes  60  by inlet air lines  84  connected to the heated air source  98  and extending through the caps  82 . In one embodiment, the caps  82  include apertures  85  formed therethrough. Additional heated air from the oven is entrained by the pressurized, heated air to flow through the apertures  85  and into the wide ends  66  of the tapered tubes  60 . This additional heated air further facilitates heating the tubes  60  as it flows through the tubes and out the narrow ends  68 . 
   In another embodiment, the passage  30  are formed before other portions of the barrier body  28  to further ensure proper formation of the passages  30 . Accordingly, the mold  50  includes an outer shell  86  spaced a distance from the mold shell  52  to create an air space  88  between the mold shell  52  and the outer shell  86 . The air space  88  delays heating of the mold shell  52  in the molding oven and allows the resin material  80  to adhere first to the tapered tubes  60  and thereby form the passages  30  prior to adhering and forming on the other portions of the mold shell  52 .  FIG. 5B  depicts the mold  50  after all of the wall surfaces  90  of the barrier body  28  have formed in the interior cavity  54  of the mold during the rotational molding process. 
   Due to the large size of the barrier body  28 , and to the increased surface area caused by the tapered tubes  60  used to form the passages  30  through the barrier body  28 , there is a tendency for the barrier body  28  to stick in the mold  50 . Difficulty removing the barrier body  28  from the mold  50  is exacerbated due to the shrinkage of the fused resin material  80  on the interior surfaces, particularly the tapered tubes  60 , once the barrier body  28  has been formed. To facilitate removing the barrier body  28  from the mold  50 , the mold  50  is outfitted with anchors  92  disposed in the side of the mold that forms the second sidewall  18  of the barrier body  28 . 
   In the embodiment shown, the anchors  92  are threaded inserts, such as part no. F2-CT38-⅜-16×0.5 available from Rotaloc International, LLC of Littleton, Colo. The threaded inserts are secured within the interior cavity  54  of the mold  50  by threaded rods  94  that extend through the mold shell  52  and outer shell  86 . The threaded rods  94  may be secured to the mold  50  by nuts  96  provided on the threaded rod  94 . Alternatively, the threaded inserts may be secured to the interior cavity  54  of the mold  50  by appropriately sized bolts. As the resin material  80  melts and fuses together, the anchors  92  become embedded in the second sidewall  18  and help to reduce the shrinkage of the barrier body  28  near the tubes  60 . 
   After the resin material has adhered to and formed the walls  90  of the barrier body  28  on the interior surfaces of the mold  50 , the mold is removed from the oven and allowed to cool. Cooling may be accomplished by ambient air, forced air, water quench, or various combinations thereof. When the mold  50  and formed barrier body  28  have cooled, the core plugs  72  are removed and the clamps  57  are released so that the lower section  58  of the mold  50 , to which the wide ends  66  of the tapered tubes  60  are attached, may be separated from the upper section  56  of the mold. The barrier body  28  remains secured to the upper section  56  of the mold by the anchors  92  attached thereto, as depicted in  FIG. 5C . The threaded rods  94  or bolts may be removed from the upper portion  56  of the mold  50  to release the threaded inserts  92  and the barrier body  28  may then be removed from the upper portion  56  of the mold  50 , as depicted in  FIG. 5D . 
   In another embodiment of the invention, the barrier body  28  includes an anchor  92  formed into the second sidewall  18  and associated with each of the passages  30  formed through the barrier body  28 , as depicted in  FIG. 6 . In this embodiment, each anchor  92  is located on the second sidewall  18  along a line  100  extending from a geometric center  102  of the second sidewall  18  and through the axial center  104  of the aperture  34  that is respectively associated with the anchor  92 . By positioning the anchors  92  in this fashion, the anchors resist shrinkage of the wall surfaces  90  in the vicinity of the tubes  60  of the mold  50 , after the barrier body  28  is formed in the mold  50 , so that the barrier body  28  may be more easily removed from the mold, as described above. 
     FIG. 7  depicts another exemplary barrier  10   a  similar to barrier  10  described above, but having non-tapered passages  30   a  extending between the first and second sidewalls  16 ,  18 . In  FIG. 7 , features corresponding to similar features of barrier  10  have been similarly numbered. Barrier  10   a  further includes baffles  106  coupled to the second sidewall  18 , proximate the second apertures  34   a , to help dissipate wave energy as water is forced through the passages  30   a . In the embodiment shown, the baffles  106  comprise flaps of material that are fixed to the second sidewall  18  such that the flaps are biased to cover one or more of the second apertures  34   a . As water is forced through the passages  30   a  by wave action, the baffles  106  are moved outwardly, away from the sidewall  18 , by the water. The water is thereafter ejected from the second apertures  34   a  as described above. After the water has passed out of the second apertures  34   a , baffles  160  return to their original positions covering the second apertures  34   a . As water that was ejected behind barrier  10   a  returns toward the shoreline, baffles  160  prevent the water from re-entering the passages  30   a . Accordingly, the baffles  160  further slow the flow of water toward the shoreline to facilitate settling sand out of the water. If desired, one or more of the second apertures  34   a  may be left uncovered by baffles  160 , to provide a path for the water returning toward the shoreline. 
     FIG. 8  depicts the landward-facing side of a barrier wall  24  formed by a plurality of barriers  10 ,  10   a  wherein adjacent barriers are secured together by coupling members. The coupling members further stabilize the individual barriers  10 ,  10   a  against movement by waves that impact the barriers. In one embodiment, the coupling members comprise flexible cables or straps  110  routed through the passages  30 ,  30   a  of adjacent barriers  10 ,  10   a . The ends of the straps  110  may be secured together by crimp fasteners  111 , splices, rivets, turnbuckles, or any other suitable method. In another embodiment, the coupling members comprise tethers  112  that are secured to respective anchors  92  on the second sides  18  of adjacent barriers  10 ,  10   a . When the anchors  92  comprise threaded inserts as described above, the tethers  112  may be secured to the anchors  92  by fasteners  114 . While the tethers  112  are shown and described herein as being secured to the second sides  18  of the barriers  10 ,  10   a , it will be appreciated that additional tethers  112  may be secured to the first sides of the barriers in a similar fashion. The straps  110  and tethers  112  may be formed from any material suitable for securing the barriers together and resisting exposure to seawater and the environment. In one embodiment, the straps  110  and tethers  112  are formed from nylon material. 
   While the present invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of the general inventive concept.