US20030044233A1

US20030044233A1 - Porous groin with flotation support

Info

Publication number: US20030044233A1
Application number: US10/232,076
Authority: US
Inventors: Wallace Hillard; Jeffrey Allain
Original assignee: SAND WEB TECHNOLOGIES Inc
Current assignee: SAND WEB TECHNOLOGIES Inc
Priority date: 2001-08-31
Filing date: 2002-08-30
Publication date: 2003-03-06
Also published as: WO2003021046A3; AU2002329939A1; WO2003021046A2

Abstract

An adjustably compliant porous groin and method for use in restoring an eroding shoreline. The compliant porous groin has a barrier suspended by flotation support within a sediment laden eroding water flow of the shoreline with the water flow passing through at least a portion of the barrier, and the bottom edge of the barrier retained proximate to the seabed. The barrier is compliant such that the water flow impacting the barrier is slowed whereby suspended sediment in the water flow accretes to renourish the shoreline.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser. No. 60/364,465, filed on Mar. 15, 2002, and is a continuation-in-part of U.S. Utility Application Ser. No. 09/943,706 filed on Aug. 31, 2001.[0001]

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to apparatuses and methods to restore or prevent erosion of shorelines and beaches. More particularly, the present invention relates to an apparatus and method for shoreline reclamation that uses a porous groin with flotation support, placed in the water proximate to the shoreline, and the structure causes accretion of sediment suspended in the water.

2. Description of the Related Art

Shorelines on bodies of moving water, such as rivers and oceans, will erode from natural processes removing material from the shoreline. This erosive process is sometimes referred to as “scour,” and the natural processes of movement of material along a coastal shoreline are referred to as littoral processes. In scour, the moving water suspends the material at one location in the flowing water and then redeposits the material at some other location. Many factors specific to the particular shoreline and water velocities can enhance erosion phenomenon.

One significant factor is the consistency of the material comprising the shoreline. A sandy beach is easily eroded by a slow and steady stream of water, and can be quickly eroded in very turbulent and fast moving water such as the seas associated with a major storm. Conversely, shoreline comprised of mostly rocks or larger sediment will be much less susceptible to erosion.

Shoreline erosion is a serious problem because most of the urban areas of the world are ports having urban development right up to the shoreline. There are often structural improvements present at and near the shoreline, such as private beach homes, hotels, bridges, retaining structures, and the like, and shoreline erosion progressively undermines the foundations thereof and threatens the physical integrity of the structures over time. There are also many regions with beach tourism as their main industry, and thus, beach erosion can cause these regions significant economic harm by removing the main tourist attraction.

There have been many devices and methods of hydraulic and earth engineering employed in the attempt to preserve shorelines or other areas subject to the erosive influence of moving water. The main method of combating erosion is to simply renourish an eroding beach with a fresh supply of dredged sand. This method has many problems associated with it however. The dredged sand often does not match the existing color of sand on the beach and diminishes the aesthetic appearance of the beach. The dredged sand can also contain rocks or other solid objects that can hinder water sports such as swimming or surfing, and can hurt the bare feet of waders upon the renourished beach.

Other methods to prevent shoreline erosion fortify the eroding shoreline with blocks, cement and the like so as to form a prophylactic layer over the region of the shoreline that would otherwise be subject to the erosive effects of the moving water. However, due to the weight and bulk of the fortifying materials, such “armoring” techniques are often difficult to install on the shoreline and adequately anchor the armor to the underlying shoreline, whether beach, bank or both. The armored structures often result in permanent structures that are not easily removed from the shoreline and prevent full enjoyment of the region of the shoreline that they overlay.

Jetties or groins are also known for attempting to control shoreline erosion. As is well known to those skilled in the art, each shoreline has a natural water direction and flow rate in accord with which the erosive flow migrates. In the typical construction, a jetty of stone or other permanent formation is built into the shore so as to form a jetty traverse the natural flow direction of the shoreline. While the jetty has the advantageous effect of promoting local sediment deposition, the jetty has a distinct disadvantage in that it causes downstream and upstream erosion. And if too many jetties are installed along a given region of shoreline, the jetties may alter the dynamic equilibrium of the shoreline and undesirably change the shape of the beach as a whole, especially when the shoreline is subject to a significant erosive event such as a storm or flood.

There are other shore and bank protection techniques and devices known in the art that attempt to control erosion by attenuating the energy, velocity, and/or direction of a potentially erosive water flow with the use of temporary structures placed on the shoreline. Several of these devices are porous groin structures using either flexible or rigid nets, screens, or filters placed on the shoreline substantially perpendicularly to the shoreline and extending into the surf. The porous groins are placed in the tidal and longshore currents and function much in the same way as a jetty to causes sand to accrete around the porous groin. The porous groin must be constantly moved or removed from the accreting sand or else extreme force must be used to dislodge the porous groin from the accreted sediment. Further, the forces of the surf can often dislodge portions of the groin that are constantly impacted by the water flow.

The porous groin structures of the prior art are often supported by stanchions driven into the seabed at intervals along the length of the groin. The installation and removal of the plurality of stanchions is labor intensive. In a typical beach restoration project, multiple porous groins are positioned along the beach, extending out into the surf with a plurality of stanchions integral with each groin. In addition to the labor involved, the rows of stanchions projecting above the sea result in an undesirable visual impediment to beachgoers. As the porous groins accrete sand, the groin must be constantly lifted from the accreted sediment by hand or mechanical means. Such lifting of the groin is labor intensive if performed by hand. Furthermore, mechanical means to perform such lifting are impractical in the ocean environment. The stanchions supporting the groin may also require partial extraction from the accreted material to facilitate removal at the end of the project.

Accordingly, it would be advantageous to provide a device and method for shoreline restoration that uses temporary structures to renourish the beach. Such device and method should renourish the beach without adversely altering the surrounding shoreline, and should use a minimum number of stanchions or other supporting structure. It is also advantageous to avoid the necessity of periodically lifting the net from the accreted sediment by hand. The device and method should also allow for an adjustably compliant suspension of the porous groin within the impacting surf, while insuring such temporary structures are not significantly dislodged by the wave action and current. It is thus to such a shoreline reclamation device and method that the present invention is primarily directed.

SUMMARY OF THE INVENTION

The disadvantages of the prior art are overcome by the present invention which, in one aspect, is an adjustably compliant porous groin for use in restoring an eroding shoreline. The shoreline has an eroding water flow impacting upon it that contains suspended solids. The eroding water flow has a periodic high and low tidal surge. The adjustably compliant porous barrier is suspended by flotation support in the eroding water flow. The barrier has a bottom edge which is retained proximate to the seabed of the shoreline, and a top edge. The compliant porous barrier causes the accretion of the suspended solids from the water flow thereby restoring the eroding shoreline.

The compliant porous groin comprises a flexible mesh which is suspended by flotation support in the eroding water flow. The barrier may be made of other materials such as semi-rigid plastic or webbing. The flotation support comprises floats attached to the barrier top edge. The floats are restrained to the seabed such that the barrier top edge is suspended by the flotation support at the height of mean low tide for all tide levels. The flotation support may also include intermediate floats attached between the barrier top and bottom edges. The bottom edge of the barrier is preferably retained proximate to the seabed by a weight affixed to the barrier bottom edge, or may be retained by tethering to a seabed anchor, or the barrier may have both a weighted bottom edge and be tethered to the seabed. In order to make the apparatus visible to swimmers and boaters, a marker float is tethered to the barrier.

In another aspect, the barrier bottom edge is retained proximate to the seabed by a restraint tether attached to the barrier bottom edge. The restraint tether then slidably engages a seabed anchor, or other anchoring means, and then is affixed to a restraint float. A flotation force on the restraint float causes a tension in the restraint tether, which pulls down on the barrier bottom edge restraining the bottom edge to the seabed.

In yet another aspect, the barrier adjustably compliant porous groin is constructed of a material having a specific gravity in seawater between 0.9 and 1.1. The porous groin may also be constructed from a material having gas filled, sealed internal voids. In this aspect the porous groin requires little additional flotation support and is extremely compliant to the impacting surf.

In yet another aspect, the compliant porous barrier is suspended by at least one stanchion driven into the seabed. The bottom edge of the compliant porous barrier is slidably restrained to the stanchion. The slidably restraint of the barrier bottom edge allows elevation of the bottom edge as the apparatus accretes sediment.

In yet another aspect, the compliant porous groin comprises a compliant porous barrier having a top edge and a bottom edge, the barrier suspended within the eroding water flow. The barrier bottom edge is retained proximate to the seabed by a restraint tether attached at one end to the barrier bottom edge. A restraint float is attached to the opposing end of the restraint tether, and the restraint tether slidably engages a seabed anchor between the attachment point of the barrier bottom edge and the attachment point of the restraint float. A flotation force on the restraint float causes a tension in the restraint tether. The restraint tether then pulls the barrier bottom edge down to the seabed. The compliant porous barrier causes the accretion of the suspended solids from the water flow thereby restoring the eroding shoreline.

The invention further provides a method restoring an eroding shoreline, the shoreline having an eroding water flow thereon and a seabed. The eroding water flow including suspended sediments therein and having a periodic high and low tidal surge. The method including the steps of placing a compliant porous barrier within the eroding water flow such that the barrier is suspended in the eroding water flow by flotation support, the barrier having a top edge and a bottom edge, the barrier bottom edge being retained proximate to the seabed, the barrier being adjustably compliant to the impacting water flow. Accreting sediment from the eroding water flow wherein the compliant porous barrier causes the accretion of the suspended solids from the eroding water flow thereby restoring the eroding shoreline. The method preferably further includes the steps of lifting the barrier out to the accreting sediment as sediment accretes from the water flow to cover the bottom edge of the barrier, and removing the barrier from the shoreline after the beach has been renourished.

If the method includes the step of lifting the barrier out of the accreting sediment, then the method preferably includes the steps of attaching one end of an extraction line to at least the barrier bottom edge, attaching the opposing end of the extraction line to an extraction float, and elevating the bottom edge of the barrier from the accreting solids when the periodic high tidal surge immerses the extraction float and the extraction float pulls upward upon the extraction line.

The step of retaining the barrier bottom edge proximate to the seabed preferably includes the steps of attaching one end of a restraint tether to the barrier bottom edge, attaching an opposing end of the restraint tether to a restraint, slidably engaging a seabed anchor on the restraint tether between the barrier bottom edge and the restraint float, and wherein flotation forces on the restraint float cause a tension in the restrain tether, the restraint tether sliding in the seabed anchor and pulling the barrier bottom edge towards the seabed.

These and other aspects of the invention will become apparent from the following description of the preferred embodiments taken in conjunction with the following drawings. As would be obvious to one skilled in the art, many variations and modifications of the invention may be effected without departing from the spirit and scope of the novel concepts of the disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side-perspective view of the apparatus for shoreline reclamation installed on a shoreline, and particularly illustrating the flotation supports, porous groin, seabed anchors and tether lines of the apparatus at low tide. [0024]
FIG. 2 is a side-perspective view of the apparatus of FIG. 1, illustrating a section of the porous groin having flotation supports, intermediate floatation supports, tether lines, seabed anchors, marker floats, and showing the high and low tide level of the shoreline. [0025]
FIG. 3 is a side-perspective view of the apparatus of FIG. 1, illustrating flotation supports, tether lines, seabed anchors, a weighted bottom edge, and showing the high and low tide level of the shoreline. [0026]
FIG. 4 is a side-perspective view of the apparatus of FIG. 1, illustrating flotation supports, flotation restraints, and showing the high and low tide level of the shoreline. [0027]
FIG. 5 is a side-perspective view of the apparatus of FIG. 1, illustrating a flotation supports, flotation restraints, flotation extraction, and showing the high and low tide level of the shoreline. [0028]
FIG. 6 is a side-perspective view of an apparatus for shoreline reclamation using stanchions, illustrating flotation supports, flotation extraction, and showing the high and low water levels of the shoreline.[0029]

DETAILED DESCRIPTION OF THE INVENTION

The porous groin apparatus has a porous barrier suspended in the eroding water flow. The barrier is compliant to the impacting water such that the water flow impacting the compliant porous barrier is slowed whereby sand accretes from the water flow. The compliance of the porous barrier to the impacting surf directly affects the sediment accretion rate. The porous groin must be adjustably compliant to the impacting surf to optimize the sand accretion rate. Prior art beach restoration devices suspend or hang the porous groin in the impacting surf from an upper line or cable, however this method of suspending the groin does not result in a porous groin that is optimally compliant, nor does it allow adjustment of the compliance of the porous groin to the impacting surf. While a compliant barrier optimizes the sand accretion rate, the porous groin device must not be so compliant as to be dislodged by the impacting surf or a storm. [0030]
With reference to the figures in which like numerals represent like elements throughout, FIG. 1 is a side view of one embodiment of the [0031] porous groin apparatus 10 for shoreline reclamation. In FIG. 1, the ocean level is depicted at low tide level 36. In the apparatus 10, a compliant porous barrier, shown here as a mesh net 16, is supported in the water above the seabed 15. A plurality of flotation supports 12 are attached to the upper edge 17 of the mesh net 16 to elevate the mesh net above the seabed 15. The flotation supports 12 and mesh net 16 extend from the waterline into the surf from the shoreline. The flotation supports 12 can be made of any buoyant material such as air filled bladders, molded or cast polyethylene (PET), cork, or other material as is known in the art. The flotation supports 12 may be a plurality of individual floats as shown in FIG. 1, or may be a continuous float stretching along the mesh net 16. The porous groin is made of a material compliant to the impacting eroding water flow, such as the mesh net 16 shown here, which can be made from an organic material, or a plastic material such as nylon or other semi-rigid plastic webbing or mesh, or other interwoven series of members.
The [0032] bottom edge 18 of the mesh net 16 is attached to a plurality of seabed anchors 22 spaced along the length of the mesh net 16. Tether lines 24 are attached to the flotation supports 12 at one end, are woven down through the material of the mesh net 16, and attached to seabed anchors 22 at the other end. The seabed anchors 22 are shown here as metal spikes driven into the seabed, but may be a weight on the seabed, or other anchoring devices known in the art. The seabed anchors 22 have a loop on the upper end which extends above the seabed 15 after installation and allows the attachment of a line, such as tether line 24. In operation, the mesh net material is stretched between the bottom edge 18 and the flotation supports 12 by the buoyant force generated by the flotation supports 12. The flotation supports 12 provide a sufficient buoyant force to lift the mesh net 16 off the seabed 15, but will not lift the bottom edge 18 off the seabed 15, nor pull the mesh net 16 bottom edge 18 free from the seabed anchors 22. The mesh net 16 may also have a weighted bottom edge 18 to restrain it to the seabed 15, or the mesh net 16 may have both a weighted bottom edge 18 and be attached to seabed anchors 22.
In one embodiment of the [0033] apparatus 10, the flotation supports 12 are an elastic bladder that is inflated with air to provide a buoyant force. The buoyant force provided by the elastic bladders may be easily adjusted by varying the amount of inflation of the individual bladders. An adjustment to the buoyant force acting upon the mesh net 16 changes the compliance of the mesh net 16 to the impacting surf. For example, a high buoyant force generated by relatively large flotation supports 12 will result in the mesh net being pulled taut between the flotation support 12 and mesh net bottom edge 18, thus resisting deflection by the impacting waves and current. Conversely, a smaller flotation support 12 will result in a lower tension in mesh net 16 and the mesh net being more compliant, or yielding to the impacting surf.
Adjustment of the compliance of the net allows optimization of the sand accretion rate of the device when installed along a shoreline considering such factors as prevailing surf conditions, groin pore size, sand grain size, etc. Additionally, the buoyant force can be adjusted along the length of the porous groin to accommodate the changing weight of the mesh net [0034] 16 when the net extends a greater height above the seabed as the apparatus 10 extends from the shoreline into deeper water.
In another embodiment, flotation supports [0035] 12 are fixed volume, molded or cast polyethylene floats. The fixed volume flotation supports 12 provide a predictable buoyant force when immersed in the surf. The flotation supports 12 are sized to provide the proper buoyant force required at each flotation support 12 application point along the mesh net 16. The buoyant force is adjusted by replacing the flotation support 12 with a different fixed volume flotation support, or by adding additional flotation supports 12, or by removing a select portion of the flotation supports 12. By adjusting the buoyant force acting on the net at each flotation support 12, the compliance of the mesh net 16 to the impacting surf is optimized along the length of the net.
As shown in FIG. 2, in another embodiment the flotation supports [0036] 12 are attached to the upper portion of the mesh net 16, and intermediate flotation supports 14 are also attached to the mesh net 16 at varying elevations off the seabed. To aid in distributing the buoyant force to the mesh net 16, the intermediate floatation supports 14 are also attached to tether lines 24. When only upper flotation supports 12 are used, the net material will be in tension vertically as the weight of netting material is held off the seabed. Vertical tension within the mesh net 16 is undesirable as the tension reduces the compliance of the net to the impacting surf. The tension, per unit of length, that the mesh net is subjected too at any elevation of the seabed is at least the weight of a unit length of the mesh net, in seawater, below the elevation of interest. Stated another way, at a given vertical elevation off the seabed the portion of the mesh net 16 below the point of interest hangs from the portion of the mesh net 16 above the point of interest. The lower portion of the mesh net 16 is supported by the upper portion of the mesh net 16 and thus generates vertical tension within the netting material. For this reason, the mesh net 16 is subjected to a non-uniform tension measured at different elevations off the seabed. The vertical tension is at a maximum value at the upper edge 17 of the mesh net 16, and at a minimum value at the bottom edge 18 of the mesh net. It is important to note that the weight of the mesh net, in seawater, as mentioned above is the specific gravity of the mesh net 16 material in seawater, multiplied by the effective volume of seawater displaced by the portion of the mesh net 16 of interest.
Affixing intermediate flotation supports [0037] 14 vertically down the face of the mesh net 16 will result in a more uniform buoyant force acting upon the mesh net. The uniform buoyant force will lower the vertical tension in the mesh net 16 between a flotation support 12 and the lower intermediate flotation support 14, and between intermediate flotation support 14 and the mesh net bottom edge 18, thus resulting in a porous groin apparatus 10 that is more compliant to the impacting surf. The lower vertical tension in the mesh net 16 makes the apparatus 10 more compliant since the mesh net 16 will deflect more easily within the impacting surf.
The [0038] entire mesh net 16, with the exception of the bottom edge 18, is also easily deflected by the impacting surf since the mesh net 16 is not strongly urged to a flotation position directly above the restrained bottom edge 18. In this manner, the mesh net 16 may wash gently from side to side as the net is impacted by the surf. The compliance of the mesh net 16 to the impacting surf is optimized at vertical elevations off the seabed by altering the buoyant force generated by the intermediate flotation supports 14 at each elevation. The buoyant force is altered by varying the intermediate flotation supports 14 volume, or by adding additional intermediate flotation supports 14, or by removing select intermediate flotation supports 14.
As also shown in FIG. 2, the length of [0039] tether lines 24 are such that the flotation supports 12 are restrained vertically off the seabed at the approximate low tide level 36. At tide levels above low tide level 36, such as high tide level 43, the apparatus is completely immersed in the water. This ensures the porous groin apparatus 10 will not drift excessively in the prevailing surf. Marker floats 26 are be tethered to the upper portion of the mesh net 16 to indicate the presence of the net at high tide level 34 when the mesh net 16 is restrained below the surface of the water. The marker floats 26 may be brightly colored with for example international orange paint, and include warnings to swimmers and boaters.
In another embodiment of the invention, the porous groin such as [0040] mesh net 16 is comprised of a material having a specific gravity very close to that of seawater. As the specific gravity of the mesh net material in seawater approaches 1, or stated another way, as the mesh net 16 is constructed of a material that almost floats in seawater, the vertical tension within the mesh net 16 is minimized. The optimal mesh net 16 material will have a specific gravity approaching 1, or slightly below 1, which allows maximizing the compliance of the mesh net 16 to the impacting surf, and therefore, maximizing the sand accretion rate of the porous groin apparatus 10. In this embodiment, the mesh net would have an approximately neutral buoyancy and would require only a small flotation support on the mesh net upper portion. Such a groin construction would be extremely compliant to the impacting surf. The material comprising the mesh net will have a specific gravity in seawater of between approximately 0.9 and 1.1. The body of the mesh net 16 in such embodiment is comprised of specially formulated polyethylene plastic (PET), or other suitable material. The material comprising the mesh net 16 may also have enclosed hollow voids within the material structure, each void filled with gas, such that the structure attains a specific gravity of between approximately 0.9 and 1.1.
As shown in FIG. 3, in another embodiment, the mesh [0041] net bottom edge 18 is not attached to the seabed anchors 22. The bottom edge 18 of the mesh net 16 is weighted with a steel chain 19 woven through the mesh material to retain the bottom edge 18 proximate to the seabed 15. The tether lines 24 pass through and slidably engage the bottom edge 18 of the mesh net 16 and are then attached to the seabed anchors 22. The tether lines 24 engage the bottom edge 18 of the net 16 by passing through an opening in the mesh material and through a link of the steel chain 19 at the mesh net 16 bottom edge 18 such that the tether line 24 may slide through the link. The tether lines 24 allow vertical movement of the bottom edge 18, but restrict substantial movement of the porous groin structure 10 along the seabed 15. The tether lines 24 allow the bottom edge 18 of the mesh net 16 to be easily lifted out of the accreted sediment by sliding the bottom edge 18 upward along the tether line 24, without necessitating physically elevating the seabed anchors 22 in the seabed 15 each time the net is lifted. As sand is accreted, the seabed anchors 22 become deeply buried within the accreted material. At the end of the reclamation process the seabed anchors 22 are pulled free from the seabed and accreted material using the tether lines 24. It may be necessary to use jet-pumping, manually digging, or other extraction means to facilitate the removal of the seabed anchors 22.
As shown in FIG. 4, in another embodiment [0042] restraint tether lines 30 and restraint floats 32 are used to retain the bottom edge 18 of the mesh net 16 proximate to the seabed. In this embodiment, the tether lines 24 are secured to the bottom edge 18 of the mesh net 16. The restraint tether lines 30 are secured to the bottom edge 18 of the net 16 at one end and slidably engage the seabed anchors 22 by passing through loops in the seabed anchors 22. On the opposing end of the restraint tether lines 30 a restraint float 32 is attached. As the restraint float 32 is immersed in the surf, the restraint tether line 30 is pulled taut, the restraint tether line 30 slides in the seabed anchor 22, and pulls the bottom edge 18 towards the seabed 15. Herein, to pull the bottom edge 18 towards the seabed is to apply a force to the bottom edge 18 such that the bottom edge 18 is urged to move closer to the seabed, i.e. the force is downward in the direction of the seabed. The volume of the restraint float 32 is selected to provide an appropriate restraining force on the bottom edge 18 of the mesh net 16 at particular locations on the groin 10. For example, the volume of the restraint float 32 may be increased as the apparatus 10 extends outward from the shore and into deeper water since the vertical height of the mesh net 16 above the seabed increases. In this manner, the rigidity with which the bottom edge 18 is restrained to the seabed 15 is adjusted and optimized at individual locations along the groin. The bottom edge 18 of the mesh net 16 may also be weighted by a steel chain, as shown in the embodiment of FIG. 3, to further aid in retaining the bottom edge 18 proximate to the seabed 15.
The effective length of the [0043] restraint tether lines 30 is adjusted by changed the location of the restraint float 32 along the restraint tether line 30. The effective length of the restraint tether lines 30 are adjusted such that the restraint floats 32 will be constantly immersed in the water below the low tide level 36. When the bottom edge 18 of the net 16 is positioned on top of the accreted sediment, the restraint floats 32 will merely be pulled deeper below the water surface. In this manner the bottom edge 18 of the mesh net 16 is restrained to the seabed 15 with a constant force regardless of the tidal level. Storm restraint lines 33, are attached to the seabed anchors 22, and the bottom edge 18 of the net 16 to preclude a radical repositioning of the apparatus 10 in heavy seas. The storm restraint lines 33 are sized to allow the bottom edge 18 of the mesh net 16 to be raised as sand is accreted during the restoration of the beach.
The compliant property of a porous groin system with flotation supports [0044] 12 and intermediate floatation supports 14 allows the use of a mesh net 16 having a finer porosity. In any porous groin system, a finer porosity generates higher forces upon the groin system from wave load when impacted by the prevailing surf since the porous body provides a greater impediment to the impacting surf. Over time, such high forces may damage more rigid groin supporting means such as stanchions, and may damage the body of the porous groin itself. The compliant nature of the flotation supports 12 and intermediate floatation supports 14 of the apparatus 10, absorb and dissipate the energy of the impacting surf with no detrimental effects to the apparatus. The apparatus may thus use a finer porosity than was practical with prior art solutions. Preferably, the mesh pore size is ½ inch, however other sizes may be used.
As shown in FIG. 5, in another aspect of the present invention, the bottom edge of the net [0045] 16 is periodically elevated from the accreting sand and sediment by a float. Ocean beaches experience a high and low tide at a frequency of twice each 24 hour period. The porous groin reclamation apparatus 10 may take advantage of the changing tide level to periodically extract the bottom edge 18 of the net 16 out of the accreted sediments. The apparatus may also use the wave action at high tide periods to elevate the net 16 out of the accreted sediments, or a combination of both wave induced elevation and tidal elevation. This aspect of the invention works best for beaches experiencing a large tidal change, however the benefits of the current invention may be applied to any beach experiencing tidal action.
FIG. 5 depicts the [0046] apparatus 10 operating at high tide level 34. A plurality of extraction lines 40 are attached to the bottom edge 18 of the mesh net 16 at regular intervals. An extraction float 42 is attached along each extraction line with the position of the extraction float 42 on the extraction line 40 readily adjustable. The effective length of each extraction line, i.e. the distance along the extraction line 40 from the bottom edge 18 of the net 16 to the point of attachment of the extraction float 42, is adjusted such that the extraction float 42 will provide a lifting force on the net 16 for a 1 to 3 hour period during the mean high tide level of the surf. The effective length of each extraction line 40 will gradually vary along the length of the net 16 as the seabed becomes deeper and hence, the bottom of the net 16 is a greater distance below mean high tide. At tide levels other than mean high tide 34, such as low tide level 36, the extraction line 40 is slack with the extraction float 42 drifting in the surf beside the net 16. In this manner, the present invention eliminates the need for manual elevation of the net 16 from the accreted sediment and insures a twice daily elevation of each net 16. The extraction floats 42 also indicate the presence of the net when the mesh net 16 is restrained below the surface of the water. The extraction floats 42 may be brightly colored with for example international orange paint, and include warnings to swimmers and boaters.
The plurality of extraction floats [0047] 42 are sized to provide a constant upward extraction force on the bottom edge 18 of the net 16 during the mean high tide. The extraction floats 42 are tethered to the bottom edge 18 of the mesh net 16 at 3 foot intervals by extraction lines 40. The extraction floats 42 are sized to provide an extraction force of approximately twice the weight of the corresponding 3 foot section of the lower portion of the mesh net 16. On a porous groin equipped with restraint floats 32, as depicted in FIG. 5, the extraction floats 40 are also sized to overcome the downward force generated by restraint float 32. For a weighted bottom edge 18 in the form of a ⅜ inch chain, as depicted in the embodiment of FIG. 3, the extraction force provided by a fully immersed extraction float 40 is twice that of a 3 foot section of ⅜ inch chain. The extraction force may be adjusted by changing the volume of extraction float 42, by adding additional extraction floats 42, or by removing select extraction floats 32. Storm restraint lines 33, are attached to the seabed anchors 22, and the bottom edge 18 of the net 16 to preclude a radical repositioning of the apparatus 10 as the bottom edge of the apparatus is elevated by extraction float 42 and in heavy or stormy seas.
The extraction force may be substantially equal to the total of the weight of the bottom portion of the [0048] mesh net 16 and, if used, the restraint force generated by restraint floats 32. In this embodiment, the wave and surf action traveling down the net 16 and submerging successive extraction floats 42 will free the net bottom edge 18 from the accreted material. The optimal extraction force is likely between 1 to 2 times the combined force of the weight of the bottom portion of the mesh net and the restraint force generated by restraint float 32. If the bottom edge 18 were to become trapped in the accreted sediment, the extraction floats 42 can be made to act upon the net 16 for a greater time period by shortening the effective length of the extraction lines. The optimal combination of extraction force and the effective length of the extraction lines 40 will vary with the sand and surf conditions of the beach to restored.
The buoyant force generated by extraction floats [0049] 40 will provide a constant upward extraction force on the bottom edge of the net 16 for the 1 to 3 hours of mean high tide 34. While the extraction force provided by the extraction floats 42 is not great when compared to the force required to manually extract the net 16 by hand, the extraction force acting constantly over the 1 to 3 hour period of the submersion, or partial submersion, of the extraction floats 42, coupled with the wave and tidal action of the shoreline will slowly free the bottom edge 18 of the net 16 from the sediment accreted in the previous 12 hour period. Since the extraction force is applied twice daily by the extraction float 42, the depth the bottom edge 18 of the mesh net 16 is buried in the accreted sediment prior to mean high tide 34 will be predictably shallow.
As sediment is accreted over time, the effective length of each [0050] extraction line 40 will be reduced. This is easily and quickly accomplished by a movable clamp on the extraction line 40 above the extraction float 42 and over which the extraction float 42 cannot slide. Periodically, beach restoration personnel will swim/walk down the net 16 and reposition each clamp to shorten the effective length of each extraction line 40. For example, each extraction float 42 may be lowered 3 inches every 3 days during periods of good accretion. This operation is much less physically demanding, less time intensive, and results in less damage to the mesh net 16 than pulling successive sections of the net 16 free from the accreted sediment by hand, as was known in the prior art.
It is understood that wave action will constantly submerge extraction floats [0051] 42 along the net 16 as a wave travels down the net 16 when high tide level 34. For example, a wave with a crest height of 3 feet over the mean high tide level 34 will force the extraction floats 42 to be submerged as the wave travels the length of the net 16. The length of the extraction lines 40 may be such that the buoyant force will be supplied, i.e. the extraction line is taught with the float pulled below the surface, only when a wave is passing along the net 16 during the mean high tide 34 periods. In this embodiment, the effective lengths of the extraction lines 40 are substantially the same as the distance from the seabed to the mean high tide level. Here, the extraction forces will only be present as a wave travels down the net 16 during the 1 to 3 hour period of peak high tide. The effect will vary with the tidal surges present upon the particular beach to be restored, the time of year, the moon phase, etc.
As further shown in FIG. 5, the invention is easily applied to a floating [0052] net 16 design. There the bottom edge of the net 16 will be tethered to the seabed at interval using seabed anchors 22 and tether lines 24. The seabed anchors 22 are driven into the seabed on the up stream side of the net 16 in relation to the prevailing long-shore transport current. During mean high tide, the bottom edge 18 of the net 16 will be elevated out of the accreted sediment by extraction floats 42 and extraction lines 40. The tether lines 24 will prevent the net 16 from becoming a drift net as the bottom edge 18 of the net 16 is elevated. During periods when the bottom edge 18 is elevated, the net 16 will drift in the direction of the long-shore current, but only to the extent allowed by the storm restraint lines 33. For the majority of a 24 hour period the net 16 bottom edge will lay upon the seabed unaffected by the slack extraction lines 40.
As shown in FIG. 6, in another embodiment the [0053] extraction lines 40 and extraction floats 42 may be applied to a compliant porous groin apparatus 10 using stanchions 50, or other supports as are known in the art, driven into the seabed 15 to support the mesh net 16. FIG. 6 depicts the apparatus 10 operating at high tide level 34. In this embodiment, the bottom edge 18 of the mesh net 16 is slidably restrained against the stanchions 50 using elastic restraining straps 52 stretching from below the net 16 bottom edge 18 on the stanchion to above the net on the stanchion. The upper edge 17 of the mesh net 16 is supported by cleat 46. In this manner, the bottom edge 18 of the net 16 is restrained against the stanchions 50, but may slide in relation to the stanchion 50 as the bottom edge 18 is periodically elevated by the extraction floats 42 and extraction lines 40 during periods of high tide 34. As also shown in FIG. 6, the apparatus 10 may also use floatation supports 12, attached to the mesh net 16 at the level of low tide 36, and intermediate flotation supports 14, attached to the mesh net 16 below the level of low tide 36, to provide flotation support to the mesh net between the stanchion locations. The magnitude of the floatation support, and hence the compliance of the mesh net 16 to the impacting surf, is adjusted by varying the size of the floats 12 and 14, by adding additional floats 12 and 14, or by selectively removing floats 12 and 14.
The [0054] apparatus 10 can be constructed in a manner such that the length of the mesh net 16 is substantially perpendicular to the shoreline. Alternately, the apparatus 10 can be formed in other non-linear arrangements to maximize the sand accretion. While it is desirous to have the greatest amount of contact between the mesh net 16 and the general flow of the water to incite accretion, the force generated by the interaction upon the apparatus(es) should also be taken into consideration when securing the mesh net 16 into the shoreline and sea bottom.
While there has been shown a preferred embodiment of the present invention, it is to be understood that certain changes may be made in the forms and arrangement of the elements and steps of the method for shoreline reclamation without departing from the underlying spirit and scope of the invention. [0055]

Claims

What is claimed is:

1. An adjustably compliant porous groin for use in restoring an eroding shoreline, the shoreline having a seabed, and the shoreline having an eroding water flow impacting thereon, the eroding water flow including suspended solids therein, the eroding water flow having a periodic high and low tidal surge, the compliant porous groin comprising:

a compliant porous barrier having a top edge and a bottom edge, the barrier being suspended by flotation support within the eroding water flow;

the barrier having the bottom edge retained proximate to the seabed; and

wherein the compliant porous barrier causes the accretion of the suspended solids from the water flow thereby restoring the eroding shoreline.

2. The complaint porous groin of claim 1, wherein the compliant porous barrier is comprised of a flexible mesh.

3. The compliant porous groin of claim 1, wherein the flotation support includes at least one float attached to the barrier top edge.

4. The compliant porous groin of claim 3, wherein a tether line is attached to the float at one end, and is restrained to the seabed at the other end, such that the barrier top edge is suspended by the flotation support substantially at the height of mean low tide for all tide levels.

5. The compliant porous groin of claim 1, wherein the flotation support includes at least one intermediate float attached to the barrier, between the barrier top edge and the barrier bottom edge.

6. The compliant porous groin of claim 1, wherein a marker float is tethered to the compliant porous barrier.

7. The compliant porous groin of claim 1, wherein the barrier bottom edge is retained proximate to the seabed by tethering to a seabed anchor.

8. The compliant porous groin of claim 1, wherein the barrier bottom edge is retained proximate to the seabed by weighting the barrier bottom edge.

9. The compliant porous groin of claim 1, wherein the barrier bottom edge is retained proximate to the seabed by:

a restraint tether attached at one end to the barrier bottom edge;

a restraint float attached at to an opposing end of the restraint tether;

the restraint tether slidably engaging a seabed anchor on the restraint tether between the attachment point of the barrier bottom edge and the attachment point of the restraint float; and

wherein a flotation force on the restraint float causes a tension in the restraint tether, the restraint tether sliding in the seabed anchor and pulling the barrier bottom edge towards the seabed.

10. The compliant porous groin of claim 1, wherein the compliant porous barrier is also suspended by at least one stanchion.

11. The compliant porous groin of claim 1, wherein the barrier is constructed from a material having a specific gravity in seawater between 0.9 and 1.1.

12. The compliant porous groin of claim 1, wherein the barrier is constructed from a material having gas filled, sealed internal voids.

13. An adjustably compliant porous groin for use in restoring an eroding shoreline, the shoreline having a seabed, the shoreline having an eroding water flow impacting thereon, the eroding water flow including suspended solids therein, the eroding water flow having a periodic high and low tidal surge, the compliant porous groin comprising:

a compliant porous barrier having a top edge and a bottom edge, the barrier being suspended within the eroding water flow;

the barrier having the bottom edge retained proximate to the seabed;

an extraction line attached at one end to at least the barrier bottom edge, and attached at the other end to an extraction float;

the compliant porous barrier causing the accretion of the suspended solids from the water flow thereby restoring the eroding shoreline; and

wherein the barrier bottom edge is elevated from the accreted solids by the periodic high tidal surge immersing the extraction float, and the extraction float pulling upward upon the extraction line.

14. The compliant porous groin of claim 13, wherein the compliant porous barrier is suspended by flotation support.

15. The compliant porous groin of claim 13, wherein the compliant porous barrier is suspended by at least one stanchion.

16. The compliant porous groin of claim 15, wherein the compliant porous barrier bottom edge is slidably restrained to the stanchion.

17. A method for restoring an eroding shoreline, the shoreline having an eroding water flow thereon and a seabed, the eroding water flow including suspended sediments therein and having a periodic high and low tidal surge, the method comprising the steps of:

placing a compliant porous barrier within the eroding water flow such that the barrier is suspended in the eroding water flow by flotation support, the barrier having a top edge and a bottom edge, the barrier bottom edge being retained proximate to the seabed, the barrier being adjustably compliant to the impacting water flow; and

accreting sediment from the eroding water flow wherein the compliant porous barrier causes the accretion of the suspended solids from the eroding water flow thereby restoring the eroding shoreline.

18. The method of claim 17, further comprising a barrier lifting step for lifting the barrier out from the accreting sediment as sediment accretes from the water flow to cover the bottom edge of the barrier.

19. The method of claim 18, further comprising:

an extraction line attachment step for attaching one end of an extraction line to at least the barrier bottom edge;

an extraction float attachment step for attaching the opposing end of the extraction line to an extraction float; and

a barrier bottom edge elevation step for elevating the bottom edge of the barrier from the accreting solids when the periodic high tidal surge immerses the extraction float and the extraction float pulls upon the extraction line.

20. The method of claim 17, further comprising a removal step for removing the compliant porous barrier from the shoreline.

21. The method of claim 17, wherein the step of retaining the barrier bottom edge proximate to the seabed comprises:

a restraint tether attachment step for attaching one end of a restraint tether to the barrier bottom edge;

a restraint float attachment step for attaching an opposing end of the restraint tether to a restraint float;

an engaging step for slidably engaging a seabed anchor on the restraint tether between the barrier bottom edge and the restraint float; and

wherein flotation forces on the restraint float cause a tension in the restrain tether, the restraint tether sliding in the seabed anchor and pulling the barrier bottom edge towards the seabed.

22. A compliant porous groin for use in restoring an eroding shoreline, the shoreline having a seabed, and the shoreline having an eroding water flow impacting thereon, the eroding water flow including suspended solids therein, the eroding water flow having a periodic high and low tidal surge, the compliant porous groin comprising:

the barrier having the bottom edge retained proximate to the seabed by a restraint tether attached at one end to the barrier bottom edge, a restraint float attached at to an opposing end of the restraint tether, the restraint tether slidably engaging a seabed anchor on the restraint tether between the attachment point of the barrier bottom edge and the attachment point of the restraint float, a flotation force on the restraint float causing a tension in the restraint tether, the restraint tether sliding in the seabed anchor and pulling the barrier bottom edge towards the seabed; and