WO2003021046A2

WO2003021046A2 - Compliant porous groin and shoreline reclamation method

Info

Publication number: WO2003021046A2
Application number: PCT/US2002/027767
Authority: WO
Inventors: Wallace Hilliard; Lance Reich; Jeffrey Allain
Original assignee: Sand Web Technologies, Inc.
Priority date: 2001-08-31
Filing date: 2002-08-30
Publication date: 2003-03-13
Also published as: US20030044233A1; AU2002329939A1; WO2003021046A3

Abstract

A compliant porous groin (10) and method of use for restoring an eroding shoreline. The compliant porous groin (10) has an adjustably compliant porous barrier (14) which is suspended by flotation support (12) such that the barrier (14) is at least partially within a sediment-laden eroding water flow of the shoreline, with the water flow passing through at least a portion of the barrier (14). The barrier (14) is compliant such that the water flow impacting the barrier (14) is slowed to at least a critical accretion velocity whereby sediment suspended in the water flow accretes to replenish the shoreline.

Description

COMPLIANT POROUS GROIN AND SHORELINE RECLAMATION METHOD

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application Serial No.

60/364,465, filed on March 15, 2002, and U.S. Utility Application Serial No. 09/943,706 filed on August 31, 2001.

TECHNICAL FIELD 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 plurality of stanchions and a compliant porous barrier fastened to the stanchions to create a temporary structure that is placed in the water flow, proximate to the shoreline, and the structure causes accretion of sediment suspended in the water flow. In another aspect, the compliant porous barrier may have flotation support.

BACKGROUND 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 the 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.

Another significant factor enhancing the erosion process is the velocity of the water passing across the shoreline. In order to initiate scour, the water must move at a velocity greater than a critical "suspension velocity" to suspend the sediment of the shoreline in the moving water. The suspension velocity required to initiate scour is dependent upon many location specific factors, such as the geometric shape of the shoreline, the average velocity of the water, the average direction of flow of the water in relation to the shoreline, the depth of the water, the density of the sediment material to be transported.

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 it 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 groins 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 in much the same way as a jetty to cause 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.

Moreover, many of these structures cite their success in beach restoration as arising from the ability of the net, screen, or filter to trap larger sediment being pulled along the sea bottom to cause ridges to build-up at the base of the porous groin. However, these structures have also been used to successfully restore pure-sand beaches, i.e. where larger sediment, such as rocks, coral, shells, and the like are not significantly present in the sediment comprising the beach. Thus, the extant explanation for success of these devices is unsatisfactory given the success in restoration of pure-sand or sediment shorelines. 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 taking full advantage of the correct mechanism for the accretion of sand and sediment from the eroding water flow. 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.

DISCLOSURE OF THE INVENTION The present inventive system and method provides a compliant porous groin for restoring an eroding shoreline utilizing the particular accretion mechanism for a water flow that contains suspended sediments. The water flow has a critical accretion velocity as it flows across the eroding shoreline, and if the water flow velocity is slower than a critical accretion velocity above which sediments otherwise remain suspended in the water flow, the suspended sediments will accrete from the water flow. The compliant porous groin takes advantage of this mechanism to renourish the sediment of an eroding shoreline, such as sand on a beach. The compliant porous groin comprises at least two supports placed in the eroding shoreline with a compliant porous barrier attached to the supports such that the barrier is at least partially within the water flow of the shoreline and the water flow passes through at least a portion of the barrier. The supports are any rigid or semi-rigid structure that can support the barrier in the water flow, such as a stanchion, tripod, pole, or channel. The barrier is compliant such that the sediment-laden water flow impacting the solid portions of the barrier is slowed to at least the critical accretion velocity such that the sediment accretes from the water flow adjacent to the barrier.

The shoreline includes a beach portion that does not ordinarily have water upon it, a substantially water-covered portion, such as an inter-tidal region, and the water portion, generally below the low-tide line. The at least two supports can be placed entirely in the substantially water-covered portion, with at least one support in the beach portion and at least one support in the substantially water-covered portion, or with at least both supports in the water portion outside of the low-tide line.

The actual compliance of the barrier can be achieved through several methods. The barrier can be made of a rigid material, such as rigid plastic webbing or wire mesh, and be flexibly held to the support to be compliant to the impacting eroding water flow. Alternatively, the barrier can made of an elastic material, such as semi-rigid plastic webbing, a mesh (organic or polymer netting), or other interwoven series of members that are compliant to the impacting eroding water flow. The invention further provides a method for restoring a shoreline having a eroding water flow moving at a velocity thereacross with suspended sediments therein and having a critical accretion velocity wherein the suspended sediments accrete from the water flow if the velocity of water flow is less than the critical accretion velocity, the method including the steps of placing at least two supports in the eroding shoreline, attaching a compliant porous barrier to the at least two supports such that the barrier is at least partially within the water flow of the shoreline and the water flow passes through at least a portion of the barrier, and accreting sediment from the water flow with the compliance of the barrier slowing the water flow impacting the barrier to at least the critical accretion velocity. The method preferably further includes the steps of lifting the barrier out from the accreting sediment as sediment accretes from the water flow to cover the barrier, and removing the barrier and supports from the shoreline after the shoreline has been renourished.

If the step of attaching a compliant porous barrier to the at least two supports is attaching a rigid porous barrier to the at least two supports such that the barrier is flexibly held to the at least two supports, then the step of accreting sediment from the water flow impacting the barrier is accreting sediment from the water flow impacting the rigid barrier made compliant to the impacting water flow from the flexible attachment of the barrier to the at least two supports, the compliance of the rigid barrier slowing the impacting water flow to at least the critical accretion velocity. And if the step of attaching a compliant porous barrier to the at least two supports is attaching an elastic porous barrier to the at least two supports, then the step of accreting sediment from the water flow impacting the barrier is accreting sediment from the water flow impacting the elastic barrier that is compliant to the impacting water flow from the elasticity of the barrier, the compliance of the elastic barrier slowing the impacting water flow to at least the critical accretion velocity. The compliant porous groin thus advantageously performs shoreline restoration using the compliance of the barrier to effect the accretion of sand and sediment from an eroding water flow. The accretion can be optimized as the compliance of the barrier can be adjusted to specifically offset a given water flow such that the impacting sediment-laden water will be slowed to at least the critical accretion velocity. The compliant porous groin does not significantly interfere with the longshore transport such that its use adversely alters the shoreline surrounding the renourished area. Further, the compliant porous groin is a temporary structure that can be used to renourish the beach and be removed thereafter with almost no environmental impact. It is thus to such a shoreline reclamation device and method that the present invention is primarily directed. In another aspect, the present inventive system and method provides an adjustably compliant porous groin for 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 semirigid 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 .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.

Other objects, advantages, and features of the present invention will become apparent after review of the hereinafter set forth Brief Description of the Drawings, Detailed Description of the Invention, and the Claims. 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 DRAWINGS

Fig. 1 is a side-perspective view of the apparatus for shoreline reclamation installed on a shoreline, and particularly illustrating the supports moored in the shoreline, and the supported compliant barrier partly within the water.

Fig. 2 is a side-perspective view of the apparatus for shoreline reclamation installed on the shoreline between the high tide and low tide water lines, with the compliant barrier extending into the water from the low tide water line. Fig. 3 is an illustration of a prior art method of beach restoration with a sediment-laden water flow impacting against a planar, solid barrier such as a sea-wall, with the incoming water flow shown by vectors A, the post-impact deflected water flow shown by vectors D, and an area of turbulent flow shown by vectors B.

Fig. 4 is a further illustration of the prior art method of Fig. 3 wherein the slowed turbulent water flow of vector C has a velocity less than the critical accretion velocity of the sediment-laden water causing an area of sediment accretion adjacent the sea-wall.

Fig. 5 is an illustration of a prior art method of beach restoration with a sediment-laden water flow impacting against a fixed barrier such as slat of a slatted groin, a fence post, rail, or non-compliant wire or rope in a mesh, with the incoming water flow shown by vector A, the post-impact deflected water flow shown by vectors D, and areas of turbulent flow shown by vectors B.

Fig. 6 is a further illustration of the prior art method of Fig. 5 wherein the slowed turbulent water flow of vector C has a velocity less than the critical accretion velocity of the sediment-laden water causing an area of sediment accretion adjacent the fixed barrier. Fig. 7 is an illustration of a body of the compliant barrier of the present invention in a sediment-laden water flow with the incoming water flow shown by vector A initially encountering the body of the compliant barrier.

Fig. 8 is an illustration of the body of the compliant barrier of Fig. 7 wherein the compliance of the barrier is shown by vector X, the post-impact deflected water flow shown by vectors D, and areas of turbulent flow shown by vectors B.

Fig. 9 is a further illustration of the sediment-laden water flow of Fig. 7 wherein the slowed turbulent water flow of vectors C has a velocity less than the critical accretion velocity of the sediment-laden water causing an area of sediment accretion adjacent the body of the compliant barrier. Fig. 10 is a perspective view of a section of the beach restoration apparatus installed on a shoreline with the compliant porous barrier partly within the water.

Fig. 11 is the beach restoration apparatus of Fig. 10 with a sediment-laden water flow in the direction of Arrow F through the complaint porous barrier, and the barrier is causing sediment to accrete from the water flow onto the sea bottom.

Fig. 12 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.

Fig. 13 is a side-perspective view of the apparatus of Fig. 12, 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.

Fig. 14 is a side-perspective view of the apparatus of Fig. 12, illustrating flotation supports, tether lines, seabed anchors, a weighted bottom edge, and showing the high and low tide level of the shoreline. Fig. 15 is a side-perspective view of the apparatus of Fig. 12, illustrating flotation supports, flotation restraints, and showing the high and low tide level of the shoreline.

Fig. 16 is a side-perspective view of the apparatus of Fig. 12, illustrating a flotation supports, flotation restraints, flotation extraction, and showing the high and low tide level of the shoreline. Fig. 17 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.

MODES FOR CARRYING OUT THE INVENTION

With reference to the figures in which like numerals represent like elements throughout, Fig. 1 is a side-perspective view of the compliant porous groin 10, with a plurality of supports 12 installed on a shoreline, shown here as a beach with a seabed 16, and with a water line 18. A compliant porous barrier 14 is attached to the supports 12 such that the barrier 14 is at least partially within the water flow, i.e. beneath water line 18, of the shoreline and the water flow passes through at least a portion of the barrier 14. As is further described herein, the barrier 14 is compliant such that the water flow impacting the barrier 14 is slowed to a critical accretion velocity wherein the water flow will accrete some of the sediment suspended therein.

The supports are preferably made of a rigid or semi-rigid material, such as a metal or a polymer plastic, and should be able to resist corrosive effects if used in a saltwater shoreline. The support 12 can be stanchion as is shown in Fig. 1, or can be other shapes and configurations such as tripods, poles, channels, or other supporting structures that are known in the art. The stanchions can be made of any rigid material such as Schedule 80 PVC, galvanized steel channels, or molded or cast polyethylene (PET). One preferred construction of the stanchions as supports 12 is the use of 21bs/ft galvanized, rib-back u-shaped channels that average 12 feet in length. If portions of lengths of stanchions are required, the channel can be cut in half or to any desired length. Further, it is also preferable that the top of each support 12 is preferably highly visible, and thus can be marked with international orange paint or other bright paint, and can also include a caution light preferably on the top of the end supports 12 to make the apparatus highly visible to boaters and beachgoers.

The barrier 14 is shown in Fig. 1 as an elastic mesh net suspended from a supporting line 20 interwoven through the upper loops of the net, and also has a weighted bottom edge 22, such as a metal cable, woven through the lower loops of the net such that the lower edge of the net substantially rests upon the sea bottom. The use of the supporting line 20 and weighted bottom edge 22 are not necessary if the net or barrier 14 is stretched taught between the supports 12. The barrier 14 is attached to the supports 12 by bands 24, which can be rigid fastener, such as rigid polymer locking loops as are known in the art, or can be more flexible fasteners made of an elastomeric material. Alternately, the barrier 14 can be attached to the supports 12 only at the supporting line 20 and weighted bottom edge 22, which are respectively attached to the supports 12, and the barrier 14 does not need to be otherwise attached to the supports 12 directly. The barrier 14 is made of an elastic material compliant to the impacting eroding water flow, such as a mesh net, which can be made from an organic material or plastic material such as nylon or other semi-rigid plastic webbing or mesh, or other interwoven series of members. Alternately, the barrier 14 can be made of a rigid material, such as a metal wire mesh, a rigid plastic webbing, or other inflexible interwoven or porous material which is flexibly held to the supports 12 with a flexible or elastomeric fastener, such as bands 24, such that the barrier 14 is compliant to the impacting eroding water flow from the flexing of the bands 24 or other flexible fastener rather than the compliance occurring from the actual elasticity of the barrier 14. A combination of both an elastic barrier 14 and flexible attaching fasteners of the barrier 14, such as bands 24, can be used to create a specific amount of compliance of the barrier 14 for a given critical accretion velocity of a water flow.

The elastic webbing comprising the barrier 14 in Fig. 1 is preferably made from a flexible material, such as nylon, and can have various sizes of meshes, depending upon the sediment grain size and other factors specific to the shoreline. Various colors of webbing 14 can also be used according to existing factors at a project location, such as brackishness of water and indigenous wildlife populations. The barrier 14 can be attached to the supports 12 in individual segments or alternately, one contiguous barrier 14 can be connected to supports 12 at various points in the length of the barrier 14. If the supports 12 are stanchions installed into the shoreline and sea-bottom through known methods such as jet-pumping or mechanical driving, the stanchions are preferably installed to an approximate depth of 50% of overall length, and can be installed deeper if required due to a significant anticipated load from the surf. Other types of supports, such as tripods, are more inherently stable and do not need to be deeply embedded into the shoreline and sea-bottom in order to anchor the groin 10.

Fig. 2 is a side-perspective view of the compliant porous groin 10 installed on a beach 14 with the groin 10 and barrier 14 extending between the high tide water line 26 and low tide water line 30. The seabed 16 includes a beach portion that is not ordinarily covered with water, which extends up the beach from the high tide line 26. The beach portion may have a water flow across it during spring tides or storm events, and thus, it is advisable, but not necessary, to have the groin 10 extend onto the beach portion. There is a substantially water- covered portion of the beach, such as the inter-tidal region between the high tide line 26 and low tide line 30. The substantially-water covered portion is thus fully covered by water at high tide, as shown by high tide water level 28, and is uncovered at low tide as shown by low tide water level 32, and generally has some portion thereof covered with water in between high tide line 26 and low tide line 30. Below the low tide line 30 is the water portion of the beach that will experience a more constant eroding water flow. The supports 12 can be placed entirely in the substantially water-covered portion, i.e. between the high tide line 26 and low tide line 30. Or, the groin 10 can be placed with supports 12 extending from the substantially-water covered portion to the beach portion of the shoreline. Alternately, as shown in Fig. 2, the compliant porous groin 10 can extend completely from the water potion of the beach, i.e. below the low tide line 30, to the beach portion above the high tide line 26. It is desirous that the groin 10 be placed such that the barrier 14 is placed such that at least a portion thereof is in the water flow present at high tide, as shown by high tide water level 28, whereby the barrier 14 is constantly accreting sediment regardless of the changing of the tides.

The advantage of the compliance of the barrier 14 in accreting sediment from the water flow is illustrated in the prior art Figs. 3-6 and in Figs. 7-9. The present invention takes advantage of the superior sediment accretion performance from the movement of the solid portions of the barrier, such as a string of the net, when impacted with sediment-laden water. The erosive water flow has sediments taken from the flow across the shoreline, such as sand, suspended therein and will keep the sediment suspended therein as long as the water flow maintains a velocity above a critical accretion velocity. If the velocity of the water flow is slowed below the critical accretion velocity due to any reason, such as impact with an object or in an area of turbulence adjacent to the solid object, the sediment will accrete from the water flow. It is known in the art that interrupting the erosive water flow with solid objects, such as jetties, will cause the accretion of the sediment. However, the full interruption of the erosive water flow will also alter the natural current flow across the shoreline and causes adverse erosion of shoreline in other locations. In Figs. 3 and 4, the prior art use of a sea wall 36, such as a jetty, to impede the progress of erosive water flow is shown. Adjacent to a shoreline, the erosive water flow is comprised of a long shore transport current parallel to the shoreline and periodic waves traveling within the fluid body. The wave action represents a transient fluid velocity that is superimposed upon the average fluid flow velocity, or long shore transport current, of the body of water adjacent to the shore. In Fig. 3, Vectors A represent a portion of a wave impacting the face of the sea wall 36. Applying basic continuity principles of fluid flow and ignoring any compressibility effects, the volume of fluid impacting the sea wall face at any given increment of time due to the wave action must equal the volume of fluid traveling down the face and reflected from the seawall. In Fig. 3, the leading edge of the wave has impacted the sea wall 36 and Vectors D represent a portion of the fluid volume traveling down the face of the sea wall 36 and Vectors B represent a reflected turbulent portion of the original fluid volume. The velocity vector D of Fig. 3 is typically higher than the original wave velocity represented by Vector A of Fig. 3.

It is thus seen that a portion of the fluid flow (vectors D) actually accelerates across the face of the sea wall 36 which can cause serious erosive effects immediately adjacent to the sea wall 36. Such erosion occurring over a period of time often undermines the foundation integrity of a body placed in the erosive water flow. However, the sea wall 36 does accrete sand in that a region of turbulence occurring between the average fluid of the wave (vectors A) and the faster moving water traveling down the face of the seawall (vectors D). As shown in Fig. 3, the turbulent flow region, represented by vectors B, typically occurs as a swirl in the fluid medium forming on the trailing edge of the passing wave and adjacent the sea wall.

Typically, the turbulent region (vectors B) forms continuously along the face of the sea wall

36 as adjacent turbulent cells of swirling fluid in the wake of the impacting wave. After the wave passes, the fluid velocity within each turbulent cell begins to slow. As shown in Fig. 4, the swirling fluid gradually losses energy to reach a critical accretion velocity, shown here as vectors C, such that the water will begin to accrete any sediment contained therein at the time the vector C is attained. Consequently, the accretion zone 38 for sediment accreting from the slowed water is away from the face of the sea wall 36 and is generally a small area in comparison to the entire surface area of sea bed because the accretion zone 38 will only occur at areas of turbulence.

In the prior art Figs. 5 and 6, there is shown a rigid body 40 generally circular in cross section, such as a pole, stanchion, or wire being placed into the erosive water flow. As a wave impacts the body 40 in Fig. 5, the water velocity adjacent the body increases as the wave travels around the obstacle. In Fig. 5, the wave velocity is shown by vector A and the velocity of the water adjacent the body by vectors D. As with the sea wall of Figs. 3 and 4, turbulent regions represented by vectors B will form between the impacting fluid flow (vector A) and the higher velocity fluid (vectors D) adjacent the body. As shown in Fig. 6, after the wave passes the swirling fluid will slow to attain the critical accretion velocity (vectors C) in the region of turbulence. Thus, as shown in Fig. 6, accretion zones 42 will form outward from the body 40 in the areas of turbulence.

In contrast as shown in Figs. 7-9, the inventive compliant porous groin 10 has the solid portions of the barrier compliant at the point of impact of the wave and lessens the velocity (vector A) of the fluid deflecting off the barrier to aid the sand accretion. In Fig. 7, the wave is beginning to impact a compliant body 50, which could be an elastic body, such as a string portion of a net or a section of an interwoven member, or the compliant body 50 may be a rigid body that is flexibly attached to the supports 12. As shown in Fig. 8, the compliant body 50 moves in response to the impact of the wave. For purposes of illustration, the compliant body 50 is shown as having moved rearward a distance, represented by vector X, in response to the impact of the wave in a particular direction (vector A). During the movement of the compliant body 50 from the starting position at impact of the wave, the deflecting water flow (vectors D) is imparted with a lower velocity than would be attained from impacting a rigid barrier. The lower velocity (vectors D) lessens the erosion that would otherwise occur adjacent to the body. As with the rigid body of Figs. 5 and 6, a turbulent region (vectors B) will form adjacent the body between the impacting water flow (vector A) and the deflecting water (vectors D). As shown in Fig. 9, after the wave passes the turbulent fluid will slow to attain the critical accretion velocity (vectors C) in the region of turbulence. The reduced velocity of the deflected water flow (vectors D) results in the turbulent fluid having less energy than that imparted by impacting a rigid body. A portion of the deflected water flow is immediately slowed to the critical accretion velocity by impacting the compliant barrier. The resultant turbulent fluid of the compliant body 50 slows to the critical accretion velocity more quickly which results in a higher sand accretion rate than that of a rigid body. Additionally, the movement of the compliant body 50 over the distance (vector X) results in a larger area of turbulent flow. Thus an enlarged accretion zone 52, shown in Fig. 9, will form outward from the body 50 in the enlarged areas of turbulence.

The illustration shows that, proportional to the fixed and rigid bodies of Figs. 3-6, the compliant body 50 of Figs. 7-9 can improve the accretion rate, and effect a far greater accretion zone through the lower deflected fluid velocity in contrast to the higher deflected fluid velocity caused at impact with the rigid sea wall 36 in Figs. 3 and 4 and the rigid body 40 in Figs. 5 and 6.

Consequently, the barrier 14 is comprised of solid bodies not rigidly affixed in the water flow, such as the strings of a net or solid portions of an otherwise porous barrier, and the actual compliance of the barrier can be adjusted such that the deflecting water flow velocity (vector D in Fig. 8) is reduced and the rate of sand accretion, and size of the sand accretion zone 52 are maximized. Further, the porosity of the net can also be varied to increase or decrease overall resistance of the barrier within the water flow. It is preferred, but not necessary, that porosity be greater than 50% of area on the barrier because lower porosity significantly interferes with the water flow and increases the force load on the barrier 14 and supports 12. Moreover, the compliant body 50 cannot be infinitely compliant and will thus give some resistive force to the water flow, especially as the full elastic limit is approached for whatever compliant method is used in the groin 10, such as an elastic barrier 14 or a rigid barrier 14 flexibly attached to the supports 12.

In operation, as shown in Figs. 10 and 11, the barrier 14 is placed in water, preferably such that a portion of the barrier 14 is above the water line 18 so that the groin 10 is visible and does not pose a water hazard. The barrier 14 is also placed in the water preferably such that the barrier 14 is generally perpendicular to the direction of the main erosive water flow, which in a coastal shoreline, is typically the longshore transport, but the barrier 14 will also work with non-orthogonal water flows. In Fig. 11, once the sediment-laden water flow begins to flow through at least a portion of the barrier 14, the water flow shown in the direction of

Arrow F, the barrier 14 begins to cause the accretion of the sediment suspended in the water, as shown by the accreting sediment 60. The accreting sediment 60 also can cover the bottom edge of the barrier 14, such as weighted bottom edge 22, such that there is a covered lower edge 62 of the barrier 14. The barrier 14 should thus be occasionally pulled out of the accreting sediment 60 such that the covered bottom edge 62 does not become too buried within the accreting sediment whereby extreme force must be used to extract the barrier 14. As long as the barrier 14 is periodically raised, the entire groin 10 can be easily removed from the shoreline by detaching the barrier 14 from the supports and removing same, and then extracting the supports 12 from the beach.

As shown in Figs. 1, 2, 10 and 11, the use of the porous groin 10 thus provides a method for restoring a shoreline that has a eroding water flow moving at an velocity thereacross, which includes the steps of placing at least two supports 12 in the eroding shoreline (such as seabed 16), attaching a compliant porous barrier 14 to the at least two supports 12 such that the barrier is at least partially within the water flow of the shoreline and the water flow passes through at least a portion of the barrier, as shown in Figs. 10 and 11, and accreting sediment from the water flow with the compliance of the barrier 14 slowing the water flow impacting the barrier 14 to at least the critical accretion velocity, as shown in Fig. 11. The method can include the step of lifting the barrier 14 out from the accreting sediment 60 as sediment accretes from the water flow to cover the barrier 14, as shown by covered lower edge 62 in Fig. 11. The method also preferably includes the step of removing the barrier 14 and at least two supports 12 from the shoreline once the shoreline is renourished, thus reflecting the temporary nature of use of the compliant porous groin 10 to restore the shoreline. The step of placing at least two supports 12 in the eroding shoreline can be placing at least two supports 12 are entirely in the substantially water-covered portion of the shoreline, i.e. between the high tide line 26 and the low tide line 30, or entirely in the water beneath the low tide line 30. Otherwise, at least one support 12 can be placed in the beach portion, i.e. above the high tide line 26, and at least one support 12 can be in the substantially water- covered portion, i.e. below the high tide line 26.

As shown in Figs. 1, 2, 10 and 11, the step of attaching a compliant porous barrier 14 to the at least two supports 12 can be attaching a rigid porous barrier 14 to the at least two supports 12 such that the barrier is flexibly held to the at least two supports 12, such as with flexible fasteners similar to bands 24. In such embodiment, the step of accreting sediment from the water flow impacting the barrier 14 is accreting sediment from the water flow impacting the rigid barrier 14 made compliant to the impacting water flow from the flexible attachment to the at least two supports 12, with the compliance of the rigid barrier slowing the impacting water flow to at least the critical accretion velocity, as illustrated in Figs. 7-9. Alternately, the step of attaching a compliant porous barrier 14 to the at least two supports 12 can attaching an elastic porous barrier 14, such as the mesh in Fig. 1, to the at least two supports 12, and the step of accreting sediment from the water flow impacting the barrier 14 is accreting sediment from the water flow impacting the elastic barrier 14 that is compliant to the impacting water flow from the elasticity of the barrier 14, the compliance of the elastic barrier slowing the impacting water flow to at least the critical accretion velocity.

In another embodiment of the present invention, the porous groin is suspended by flotation support within 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.

Fig. 12 is a side view of another embodiment of the porous groin apparatus 10 for shoreline reclamation. In Fig. 12, the water is depicted at water level 18. In the apparatus 10, a compliant porous barrier, shown here as a barrier 14, is supported in the water above the seabed 16. A plurality of flotation supports 70 are attached to the upper edge 21 of the barrier 14 to elevate the mesh net above the seabed 16. The flotation supports 70 and barrier 14 extend from the waterline into the surf from the shoreline. The flotation supports 70 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 70 may be a plurality of individual floats as shown in Fig. 12, or may be a continuous float stretching along the barrier 14.

The bottom edge 22 of the barrier 14 is attached to a plurality of seabed anchors 78 spaced along the length of the barrier 14. Tether lines 74 are attached to the flotation supports 70 at one end, are woven down through the material of the barrier 14, and attached to seabed anchors 78 at the other end. The seabed anchors 78 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 78 have a loop on the upper end which extends above the seabed 16 after installation and allows the attachment of a line, such as tether line 74. In operation, the mesh net material is stretched between the bottom edge 22 and the flotation supports 70 by the buoyant force generated by the flotation supports 70. The flotation supports 70 provide a sufficient buoyant force to lift the barrier 14 off the seabed 16, but will not lift the bottom edge 22 off the seabed 16, nor pull the barrier 14 bottom edge 22 free from the seabed anchors 78. The barrier 14 may also have a weighted bottom edge 22 to restrain it to the seabed 16, or the barrier 14 may have both a weighted bottom edge 22 and be attached to seabed anchors 78.

In one embodiment of the apparatus 10, the flotation supports 70 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 barrier 14 changes the compliance of the barrier 14 to the impacting surf. For example, a high buoyant force generated by relatively large flotation supports 70 will result in the mesh net being pulled taut between the flotation support 70 and mesh net bottom edge 22, thus resisting deflection by the impacting waves and current. Conversely, a smaller flotation support 70 will result in a lower tension in barrier 14 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 barrier 14 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 70 are fixed volume, molded or cast polyethylene floats. The fixed volume flotation supports 70 provide a predictable buoyant force when immersed in the surf. The flotation supports 70 are sized to provide the proper buoyant force required at each flotation support 70 application point along the barrier 14. The buoyant force is adjusted by replacing the flotation support 70 with a different fixed volume flotation support, or by adding additional flotation supports 70, or by removing a select portion of the flotation supports 70. By adjusting the buoyant force acting on the net at each flotation support 70, the compliance of the barrier 14 to the impacting surf is optimized along the length of the net.

As shown in Fig. 13, in another embodiment the flotation supports 70 are attached to the upper portion of the barrier 14, and intermediate flotation supports 82 are also attached to the barrier 14 at varying elevations off the seabed. To aid in distributing the buoyant force to the barrier 14, the intermediate floatation supports 82 are also attached to tether lines 74.

When only upper flotation supports 70 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 barrier 14 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 barrier 14 below the point of interest hangs from the portion of the barrier 14 above the point of interest. The lower portion of the barrier 14 is supported by the upper portion of the barrier 14 and thus generates vertical tension within the netting material. For this reason, the barrier 14 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 21 of the barrier 14, and at a minimum value at the bottom edge 22 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 barrier 14 material in seawater, multiplied by the effective volume of seawater displaced by the portion of the barrier 14 of interest.

Affixing intermediate flotation supports 82 vertically down the face of the barrier 14 will result in a more uniform buoyant force acting upon the mesh net. The uniform buoyant force will lower the vertical tension in the barrier 14 between a flotation support 70 and the lower intermediate flotation support 82, and between intermediate flotation support 82 and the mesh net bottom edge 22, thus resulting in a porous groin apparatus 10 that is more compliant to the impacting surf. The lower vertical tension in the barrier 14 makes the apparatus 10 more compliant since the barrier 14 will deflect more easily within the impacting surf.

The entire barrier 14, with the exception of the bottom edge 22, is also easily deflected by the impacting surf since the barrier 14 is not strongly urged to a flotation position directly above the restrained bottom edge 22. In this manner, the barrier 14 may wash gently from side to side as the net is impacted by the surf. The compliance of the barrier 14 to the impacting surf is optimized at vertical elevations off the seabed by altering the buoyant force generated by the intermediate flotation supports 82 at each elevation. The buoyant force is altered by varying the intermediate flotation supports 82 volume, or by adding additional intermediate flotation supports 82, or by removing select intermediate flotation supports 82.

As shown in Fig. 13, the length of tether lines 74 are such that the flotation supports 70 are restrained vertically off the seabed at the approximate low tide level 32. At tide levels above low tide level 32, 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 86 are be tethered to the upper portion of the barrier 14 to indicate the presence of the net at high tide level 28 when the barrier 14 is restrained below the surface of the water. The marker floats 86 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 barrier 14 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 barrier 14 is constructed of a material that almost floats in seawater, the vertical tension within the barrier 14 is minimized. The optimal barrier 14 material will have a specific gravity approaching 1, or slightly below 1, which allows maximizing the compliance of the barrier 14 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 .9 and 1.1. The body of the barrier 14 in such embodiment is comprised of specially formulated polyethylene plastic (PET), or other suitable material. The material comprising the barrier 14 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 .9 and 1.1.

As shown in Fig. 14, in another embodiment, the mesh net bottom edge 22 is not attached to the seabed anchors 78. The bottom edge 22 of the barrier 14 is weighted with a steel chain 90 woven through the mesh material to retain the bottom edge 22 proximate to the seabed 16. The tether lines 74 pass through and slidably engage the bottom edge 22 of the barrier 14 and are then attached to the seabed anchors 78. The tether lines 74 engage the bottom edge 22 of the net 14 by passing through an opening in the mesh material and through a link of the steel chain 90 at the barrier 14 bottom edge 22 such that the tether line 74 may slide through the link. The tether lines 74 allow vertical movement of the bottom edge 22, but restrict substantial movement of the porous groin structure 10 along the seabed 16. The tether lines 74 allow the bottom edge 22 of the barrier 14 to be easily lifted out of the accreted sediment by sliding the bottom edge 22 upward along the tether line 74, without necessitating physically elevating the seabed anchors 78 in the seabed 16 each time the net is lifted. As sand is accreted, the seabed anchors 78 become deeply buried within the accreted material. At the end of the reclamation process the seabed anchors 78 are pulled free from the seabed and accreted material using the tether lines 74. It may be necessary to use jet-pumping, manually digging, or other extraction means to facilitate the removal of the seabed anchors 78.

As shown in Fig. 15, in another embodiment restraint tether lines 94 and restraint floats

92 are used to retain the bottom edge 22 of the barrier 14 proximate to the seabed. In this embodiment, the tether lines 74 are secured to the bottom edge 22 of the barrier 14. The restraint tether lines 94 are secured to the bottom edge 22 of the net 14 at one end and slidably engage the seabed anchors 78 by passing through loops in the seabed anchors 78. On the opposing end of the restraint tether lines 94 a restraint float 92 is attached. As the restraint float 92 is immersed in the surf, the restraint tether line 94 is pulled taut, the restraint tether line 94 slides in the seabed anchor 78, and pulls the bottom edge 22 towards the seabed 16. Herein, to pull the bottom edge 22 towards the seabed is to apply a force to the bottom edge 22 such that the bottom edge 22 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 92 is selected to provide an appropriate restraining force on the bottom edge 22 of the barrier 14 at particular locations on the groin 10. For example, the volume of the restraint float 92 may be increased as the apparatus 10 extends outward from the shore and into deeper water since the vertical height of the barrier 14 above the seabed increases. In this manner, the rigidity with which the bottom edge 22 is restrained to the seabed 16 is adjusted and optimized at individual locations along the groin. The bottom edge 22 of the barrier 14 may also be weighted by a steel chain, as shown in the embodiment of Fig. 14, to further aid in retaining the bottom edge 22 proximate to the seabed 16.

The effective length of the restraint tether lines 94 is adjusted by changed the location of the restraint float 92 along the restraint tether line 94. The effective length of the restraint tether lines 94 are adjusted such that the restraint floats 92 will be constantly immersed in the water below the low tide level 32. When the bottom edge 22 of the net 14 is positioned on top of the accreted sediment, the restraint floats 92 will merely be pulled deeper below the water surface. In this manner the bottom edge 22 of the barrier 14 is restrained to the seabed 16 with a constant force regardless of the tidal level. Storm restraint lines 96, are attached to the seabed anchors 78, and the bottom edge 22 of the net 14 to preclude a radical repositioning of the apparatus 10 in heavy seas. The storm restraint lines 96 are sized to allow the bottom edge 22 of the barrier 14 to be raised as sand is accreted during the restoration of the beach. The compliant property of a porous groin system with flotation supports 70 and intermediate floatation supports 82 allows the use of a barrier 14 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 70 and intermediate floatation supports 82 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 V_ inch, however other sizes may be used. As shown in Fig. 16, in another aspect of the present invention, the bottom edge of the net 14 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 74 hour period. The porous groin reclamation apparatus 10 may take advantage of the changing tide level to periodically extract the bottom edge 22 of the net 14 out of the accreted sediments. The apparatus may also use the wave action at high tide periods to elevate the net 14 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. 16 depicts the apparatus 10 operating at high tide level 28. A plurality of extraction lines 102 are attached to the bottom edge 22 of the barrier 14 at regular intervals. An extraction float 100 is attached along each extraction line with the position of the extraction float 100 on the extraction line 102 readily adjustable. The effective length of each extraction line, i.e. the distance along the extraction line 102 from the bottom edge 22 of the net 14 to the point of attachment of the extraction float 100, is adjusted such that the extraction float 100 will provide a lifting force on the net 14 for a 1 to 3 hour period during the mean high tide level of the surf. The effective length of each extraction line 102 will gradually vary along the length of the net 14 as the seabed becomes deeper and hence, the bottom of the net 14 is a greater distance below mean high tide. At tide levels other than mean high tide 28, such as low tide level 32, the extraction line 102 is slack with the extraction float 100 drifting in the surf beside the net 14. In this manner, the present invention eliminates the need for manual elevation of the net 14 from the accreted sediment and insures a twice daily elevation of each net 14. The extraction floats 100 also indicate the presence of the net when the barrier 14 is restrained below the surface of the water. The extraction floats 100 may be brightly colored with for example international orange paint, and include warnings to swimmers and boaters.

The plurality of extraction floats 100 are sized to provide a constant upward extraction force on the bottom edge 22 of the net 14 during the mean high tide. The extraction floats 100 are tethered to the bottom edge 22 of the barrier 14 at 3 foot intervals by extraction lines 102.

The extraction floats 100 are sized to provide an extraction force of approximately twice the weight of the corresponding 3 foot section of the lower portion of the barrier 14. On a porous groin equipped with restraint floats 92, as depicted in Fig. 16, the extraction floats 102 are also sized to overcome the downward force generated by restraint float 92. For a weighted bottom edge 22 in the form of a 3/8 inch chain, as depicted in the embodiment of Fig. 14, the extraction force provided by a fully immersed extraction float 102 is twice that of a 3 foot section of 3/8 inch chain. The extraction force may be adjusted by changing the volume of extraction float 100, by adding additional extraction floats 100, or by removing select extraction floats 92. Storm restraint lines 96, are attached to the seabed anchors 78, and the bottom edge 22 of the net 14 to preclude a radical repositioning of the apparatus 10 as the bottom edge of the apparatus is elevated by extraction float 100 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 barrier 14 and, if used, the restraint force generated by restraint floats 92. In this embodiment, the wave and surf action traveling down the net 14 and submerging successive extraction floats 100 will free the net bottom edge 22 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 92. If the bottom edge 22 were to become trapped in the accreted sediment, the extraction floats 100 can be made to act upon the net 14 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 102 will vary with the sand and surf conditions of the beach to restored.

The buoyant force generated by extraction floats 102 will provide a constant upward extraction force on the bottom edge of the net 14 for the 1 to 3 hours of mean high tide 28.

While the extraction force provided by the extraction floats 100 is not great when compared to the force required to manually extract the net 14 by hand, the extraction force acting constantly over the 1 to 3 hour period of the submersion, or partial submersion, of the extraction floats 100, coupled with the wave and tidal action of the shoreline will slowly free the bottom edge 22 of the net 14 from the sediment accreted in the previous 70 hour period. Since the extraction force is applied twice daily by the extraction float 100, the depth the bottom edge 22 of the barrier 14 is buried in the accreted sediment prior to mean high tide level 28 will be predictably shallow.

As sediment is accreted over time, the effective length of each extraction line 102 will be reduced. This is easily and quickly accomplished by a movable clamp on the extraction line 102 above the extraction float 100 and over which the extraction float 100 cannot slide. Periodically, beach restoration personnel will swim/walk down the net 14 and reposition each clamp to shorten the effective length of each extraction line 102. For example, each extraction float 100 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 barrier 14 than pulling successive sections of the net 14 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 100 along the net 14 as a wave travels down the net 14 when high tide level 28. For example, a wave with a crest height of 3 feet over the mean high tide level 28 will force the extraction floats 100 to be submerged as the wave travels the length of the net 14. The length of the extraction lines 102 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 14 during the mean high tide 28 periods. In this embodiment, the effective lengths of the extraction lines 102 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 14 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. 16, the invention is easily applied to a floating net 14 design.

There the bottom edge of the net 14 will be tethered to the seabed at interval using seabed anchors 78 and tether lines 74. The seabed anchors 78 are driven into the seabed on the up stream side of the net 14 in relation to the prevailing long-shore transport current. During mean high tide, the bottom edge 22 of the net 14 will be elevated out of the accreted sediment by extraction floats 100 and extraction lines 102. The tether lines 74 will prevent the net 14 from becoming a drift net as the bottom edge 22 of the net 14 is elevated. During periods when the bottom edge 22 is elevated, the net 14 will drift in the direction of the long-shore current, but only to the extent allowed by the storm restraint lines 96. For the majority of a 74 hour period the net 14 bottom edge will lay upon the seabed unaffected by the slack extraction lines 102.

As shown in Fig. 17, in another embodiment the extraction lines 102 and extraction floats 100 may be applied to a compliant porous groin apparatus 10 using stanchion supports 12, or other supports as are known in the art, driven into the seabed 16 to support the barrier 14. Fig. 17 depicts the apparatus 10 operating at high tide level 28. In this embodiment, the bottom edge 22 of the barrier 14 is slidably restrained against the stanchion supports 12 using elastic restraining straps 108 stretching from below the net 14 bottom edge 22 on the stanchion to above the net on the stanchion. The upper edge 21 of the barrier 14 is supported by cleat 110. In this manner, the bottom edge 22 of the net 14 is restrained against the stanchion supports 12, but may slide in relation to the stanchion supports 12 as the bottom edge 22 is periodically elevated by the extraction floats 100 and extraction lines 102 during periods of high tide level 28. As also shown in Fig. 17, the apparatus 10 may also use floatation supports 70, attached to the barrier 14 at the level of low tide 32, and intermediate flotation supports 82, attached to the barrier 14 below the level of low tide 32, to provide flotation support to the mesh net between the stanchion locations. The magnitude of the floatation support, and hence the compliance of the barrier 14 to the impacting surf, is adjusted by varying the size of the floats 70 and 82, by adding additional floats 70 and 82, or by selectively removing floats 70 and 82.

The apparatus 10 can be constructed in a manner such that the length of the barrier 14 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 barrier 14 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 barrier 14 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 of the flexible porous groin and steps of the method for shoreline reclamation without departing from the underlying spirit and scope of the invention. Moreover, the description of the preferred embodiment above is not intended to imply any specific definition to the terms of the Claims unless expressly stated to the contrary.

Claims

CLAIMS What is claimed is:

1. A compliant porous groin for restoring an eroding shoreline, the shoreline having a eroding water flow moving at an velocity thereacross, and the water flow including suspended sediments therein and having a critical accretion velocity wherein the suspended sediments accreting from the water flow if the velocity of water flow is less than the critical accretion velocity, the compliant porous groin comprising: at least two supports placed in an eroding shoreline; and a adjustably compliant porous barrier attached to the at least two supports such that the barrier is at least partially within the water flow of the shoreline and the water flow passes through at least a portion of the barrier, and wherein the barrier is compliant such that the water flow impacting the barrier is slowed to at least the critical accretion velocity.

2. The porous groin of claim 1, wherein the shoreline includes a beach portion and a substantially water-covered portion, and the at least two supports are placed entirely in the substantially water-covered portion.

3. The porous groin of claim 1, wherein the shoreline includes a beach portion and a substantially water-covered portion, and the at least two supports are placed such that at least one support is in the beach portion, and at least one support is in the substantially water- covered portion.

4. The porous groin of claim 1, wherein the barrier is made of a rigid material and flexibly held to the support to be compliant to the impacting eroding water flow.

5. The porous groin of claim 4, wherein the rigid material is rigid plastic webbing.

6. The porous groin of claim 4, wherein the rigid material is a wire-mesh.

7. The porous groin of claim 1, wherein the barrier is made of an elastic material compliant to the impacting eroding water flow.

8. The porous groin of claim 7, wherein the elastic material is semi-rigid plastic webbing.

9. The porous groin of claim 7, wherein the elastic material is a mesh.

10. The porous groin of claim 1 , wherein at least one of the two supports is a stanchion.

11. The porous groin of claim 1 , wherein at least one of the two supports is a tripod.

12. The porous groin of claim 1, wherein at least one of the two supports is a channel.

13. The porous groin of claim 1 , wherein the barrier is formed of an interwoven series of members.

14. An apparatus for restoring an eroding shoreline, the shoreline having a eroding water flow moving at a velocity thereacross, and the water flow including suspended sediments therein and having a critical accretion velocity wherein if the velocity of the water flow is less than the critical accretion velocity, the suspended sediments accrete from the water flow, the apparatus comprising: a support means for supporting a compliant porous barrier in an eroding shoreline; and a barrier means for causing the water flow impacting the barrier means to be slowed to at least the critical accretion velocity, the barrier means comprised of a adjustably compliant porous barrier attached to the support means such that the barrier means is at least partially within the water flow of the shoreline and the water flow passes through at least a portion of the barrier means.

15. A method for restoring a shoreline having a eroding water flow moving at an velocity thereacross, and the water flow including suspended sediments therein and having a critical accretion velocity wherein the suspended sediments accrete from the water flow if the velocity of water flow is less than the critical accretion velocity, the method comprising the steps of:

placing at least two supports in the eroding shoreline; attaching a adjustably compliant porous barrier to the at least two supports such that the barrier is at least partially within the water flow of the shoreline and the water flow passes through at least a portion of the barrier; and accreting sediment from the water flow with the compliance of the barrier slowing the water flow impacting the barrier to at least the critical accretion velocity.

16. The method of claim 15, further comprising the step of lifting the barrier out from the accreting sediment from the water flow as the accreting sediment covers the lower portion of the barrier.

17. The method of claim 15, wherein the shoreline includes a beach portion and a substantially water-covered portion, and the step of placing at least two supports in the eroding shoreline is placing at least two supports are entirely in the substantially water-covered portion of the shoreline.

18. The method of claim 15, wherein the shoreline includes a beach portion and a substantially water-covered portion, and the step of placing at least two supports in the eroding shoreline is placing the two supports in the eroding shoreline such that at least one support is in the beach portion, and at least one support is in the substantially water-covered portion.

19. The method of claim 15, wherein: the step of attaching a compliant porous barrier to the at least two supports is attaching a rigid porous barrier to the at least two supports such that the barrier is flexibly held to the at least two supports; and the step of accreting sediment from the water flow impacting the barrier is accreting sediment from the water flow impacting the rigid barrier made compliant to the impacting water flow from the flexible attached to the at least two supports, the compliance of the rigid barrier slowing the impacting water flow to at least the critical accretion velocity.

20. The method of claim 15, wherein: the step of attaching a compliant porous barrier to the at least two supports is attaching an elastic porous barrier to the at least two supports; and the step of accreting sediment from the water flow impacting the barrier is accreting sediment from the water flow impacting the elastic barrier that is compliant to the impacting water flow from the elasticity of the barrier, the compliance of the elastic barrier slowing the impacting water flow to at least the critical accretion velocity.

21. The method of claim 15, further comprising the step of removing the barrier and at least two supports from the shoreline.

22. A method for restoring a shoreline having a eroding water flow moving at a velocity thereacross, and the water flow including suspended sediments therein and having a critical accretion velocity wherein the suspended sediments accrete from the water flow if the velocity of water flow is less than the critical accretion velocity, the method comprising the steps of: a support placement step for placing at least two supports in the eroding shoreline; a barrier attachment step for attaching a adjustably compliant porous barrier to the at least two supports such that the barrier is at least partially within the water flow of the shoreline and the water flow passes through at least a portion of the barrier; and a sediment accretion step for accreting sediment from the water flow with the compliance of the barrier slowing the water flow impacting the barrier to at least the critical accretion velocity.

23. The method of claim 22, 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 lower portion of the barrier.

24. The method of claim 22, further comprising a removal step for removing the barrier and at least two supports from the shoreline.

25. 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.

26. The complaint porous groin of claim 25, wherein the compliant porous barrier is comprised of a flexible mesh.

27. The compliant porous groin of claim 25, wherein the flotation support includes at least one float attached to the barrier top edge.

28. The compliant porous groin of claim 27, 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.

29. The compliant porous groin of claim 25, wherein the flotation support includes at least one intermediate float attached to the barrier, between the barrier top edge and the barrier bottom edge.

30. The compliant porous groin of claim 25, wherein a marker float is tethered to the compliant porous barrier.

31. The compliant porous groin of claim 25, wherein the barrier bottom edge is retained proximate to the seabed by tethering to a seabed anchor.

32. The compliant porous groin of claim 25, wherein the barrier bottom edge is retained proximate to the seabed by weighting the barrier bottom edge.

33. The compliant porous groin of claim 25, 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.

34. The compliant porous groin of claim 25, wherein the compliant porous barrier is also suspended by at least one support.

35. The compliant porous groin of claim 25, wherein the barrier is constructed from a material having a specific gravity in seawater between .9 and 1.1.

36. The compliant porous groin of claim 25, wherein the barrier is constructed from a material having gas filled, sealed internal voids.

37. 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.

38. The compliant porous groin of claim 37, wherein the compliant porous barrier is suspended by flotation support.

39. The compliant porous groin of claim 37, wherein the compliant porous barrier is suspended by at least one support.

40. The compliant porous groin of claim 39, wherein the compliant porous barrier bottom edge is slidably restrained to the support.

41. 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.

42. The method of claim 41 , 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.

43. The method of claim 42, 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.

44. The method of claim 41 , further comprising a removal step for removing the compliant porous barrier from the shoreline.

45. The method of claim 41 , 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.

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