WO1996025560A1

WO1996025560A1 - Device for erosion control

Info

Publication number: WO1996025560A1
Application number: PCT/US1996/001886
Authority: WO
Inventors: Richard E. Creter; Charles W. Bowman
Original assignee: Geo-Syn Products Company
Priority date: 1995-02-16
Filing date: 1996-02-13
Publication date: 1996-08-22

Abstract

A fence for shoreline erosion control includes a plurality of posts (102, 104) and a one-piece transverse member (106) extending between the posts. The transverse member may be a high-strength, high-density polyethylene grid having a plurality of horizontal ribs (107-110) and a plurality of vertical junctions (112, 114), forming a plurality of horizontally-elongated openings (116).

Description

DEVICE FOR EROSION CONTROL

Field Of The Invention

The present invention relates to devices for protecting shorelines and in particular to a fence for preventing erosion of beaches and/or dunes caused by wave run-up and storm surges.

Background Information

It is well-known that storms can cause extensive damage to shorelines (e.g., beaches, roadways, and houses in close proximity to an ocean) . Indeed, the high wind velocities often associated with storms cause surges of water which, as they move across a beach, pick-up sand and together cause further damage to structures which they ultimately impact. Sand dunes are valuable, natural, non-structural barriers that protect and reduce damage in areas behind the dunes. However, dunes themselves are often damaged (eroded) by storms, necessitating costly repair and restoration.

Sand/snow fences are often installed along beaches to catch wind-blown sand in an effort to create and/or reinforce sand dunes. These fences are typically formed of multiple, spaced, vertically-oriented wood slats connected by metal wire, for example.

Such fences, however, are ineffective in protecting adjacent beaches and dunes from the surges of water (and high wind velocities) associated with severe storms (and, indeed, are not installed for that purpose) . Because such fences are relatively weak (particularly at the connections) , they are often destroyed during such storms. In addition, such fences are also subject to biological and chemical breakdown because of the wood composition. Finally, such fences are relatively poor in preventing sand picked-up by strong waves from being carried by the waves into the ocean as the waves retreat.

Summary Of The Invention

The present invention is directed to an upland device, and in particular a fence, preferably installed at the toe of a sand dune in order to protect the beach and dune from wave run-up and surges of water that would otherwise seriously erode the beach and dune. The fence is particularly advantageous with respect to water surges during severe storms.

The fence according to the present invention includes at least two substantially-vertical support members, which are preferably steel posts. A one-piece transverse member, which is preferably a polyethylene grid, extends between the two support members. The transverse member is supported solely by the support members (e.g., by using a weaving technique) , preferably without any fastening mechanisms between the support members and the transverse member.

The transverse member includes at least upper and lower ribs. Preferably, the ribs are horizontally oriented between vertically-oriented junctions, so as to form horizontally-elongated openings.

In operation, the fence according to the present invention is very effective in breaking wave run-up and surges, thus reducing the energy contained in the waves and the damage that the waves ultimately cause to areas behind the fence. In addition, because the fence according to the present invention is preferably made of a one-piece high-density polyethylene grid with no connections between the grid and its supporting posts, the fence is uniformly very strong, i.e., there is a continuity of high tensile strength (e.g., 130,000 lbs/ft) . As a result, damage to the fence during severe storms is largely avoided, thus preserving the fence's ability to protect the shoreline. Moreover, because large portions of the fence are composed of plastic, the fence is generally not subject to biological or chemical breakdown. Consequently, the fence is very long-lasting and requires relatively little maintenance.

Moreover, the horizontal ribs and the horizontally- elongated openings of the fence are very effective in retaining sand and, thus, preventing beach erosion. In particular, the horizontal-rib arrangement, dimensioned as in the exemplary embodiment described below (or as in any other advantageous horizontal set-up) , is much more effective than conventional vertical-slat arrangements, for example, in dropping sand out of the waves by breaking the waves upon impact with the horizontal ribs. As a result, the fence according to the present invention effectively reduces erosion by preventing dune and beach sand from being carried into the ocean by retreating waves. Indeed, it has been found that the fence according to the present invention may have, for example, over four times more sand retention capability than conventional fences.

Brief Description Of The Drawings

Figure 1 shows a partial side view of an embodiment of the fence according to the present invention.

Figure 2 shows a top view of an exemplary configuration of a section of the fence according to the present invention.

Detailed Description

Referring to Figure 1, there is shown a representative portion of a preferred embodiment of a retention fence according to the present invention. The fence includes a plurality of support members which are preferably substantially-vertically-oriented posts (only two shown) 102, 104. Each of the posts 102, 104 may be made, for example, of steel pipe of 3" diameter. The posts 102, 104 are spaced, for example, 15' apart. The support members may instead be anchoring devices, for example.

The fence further includes at least one single-piece transverse member 106 which extends between adjacent posts 102, 104. The transverse member 106 is preferably a high-strength, high-density, permeable plastic grid, and is most preferably a grid made of high-density polyethylene, having flexural rigidity, and being approximately 60% permeable. A "geogrid" is commercially available from, for example, Tensar Earth Technologies Inc. of Morrow, Georgia.

An embodiment of the transverse member 106 includes a plurality of ribs (only some of which are shown) 107-110. The ribs 107-110 are preferably oriented horizontally, but can instead be slanted, for example. The transverse member 106 preferably further includes a plurality of vertically-oriented junctions 112, 114 which connect the ribs 107-110 so as to define openings 116 between the ribs. In the preferred embodiment as shown in Figure 1, these openings 116 are horizontally-elongated (approximately oval-shaped) .

The (rigid) transverse member 106 is supported in an upright position solely by the posts 102, 104. In the preferred embodiment of the fence according to the present invention as shown in Figure l, the ribs 107-100 (between the junctions 112 and 114) are woven around the post 102. For example, the ribs 107, 109 may contact a front portion of the post 102, while the ribs 108, 110 contact a rear portion of the post 102. It is important to note that a technique other than weaving can be used. For example, the transverse member can be wrapped around an end post in order to secure the transverse member to the post. In any case, no separate mechanical fasteners are necessary in order to support the transverse member 106 with respect to the posts 102, 104.

In an exemplary embodiment of the fence according to the present invention, the transverse member 106 is dimensioned as follows: Each of the ribs 107-110 is approximately 6" long and 1/4" wide (at center) , and the distance between adjacent ribs 107-110 (at center) is approximately 3/4" (making each of the openings 116 approximately 6" in the horizontal direction and 3/4" in the vertical direction). Each of the junctions 112, 114 is approximately 3/4" wide and has a height approximately equal to the height of the fence. Therefore, for a

4 1/2' high fence, for example, the height of the posts 102, 104 and the height of the junctions 112, 114 are preferably 4 1/2' .

It should be understood that the quantities, formations and dimensions of the posts, ribs and/or junctions can vary with the particular application of the fence according to the present invention. It should also be understood that the materials used to form the posts and the transverse member can vary with the particular application of the fence according to the present invention. For example, even though the transverse member is most preferably composed of polyethylene, other types of plastics can be used, as well as other types of materials of sufficient strength.

Referring now to Figure 2, there is shown an exemplary configuration of a section of the fence according to the present invention, and in particular two separate fences arranged in a double zig-zag formation. The fences 202, 204 are positioned at a portion of a beach 206 preferably at the toe of a dune (system) 208 upland from the body of water. In this embodiment, the fences 202, 204 do not contact the water except when waves run-up toward the dune 208 during a severe storm, for example.

Each of the posts 210, 212, 214 is embedded into the beach 206 to a depth sufficient to absorb shock of direct impact on the fence from wave run-up and storm surges. If the distance between the central posts 210, 212 is 15', for example, the portions of the fences 202, 204 shown in Figure 2 extend along approximately 150' of the dune 208. The post 212 of the fence 202 and the adjacent post 214 of the fence 204 can be arranged, for example, 2' apart.

It should be understood that the principles of the present invention are equally applicable to other single- fence and multiple-fence configurations including, among others, single zig-zag, parallel and angled configurations. In addition, it should be understood that the fence can be used in locations other than at the toe of a dune. For example, the fence can also be used on narrow beaches where dune creation may not be possible because of continual damage from wave run-up and storm surges.

Claims

What Is Claimed Is:

1. A device for controlling erosion, comprising: a substantially-vertical first support member; a substantially-vertical second support member spaced from the first support member; and a one-piece transverse member extending between the first and second support members, the transverse member including an upper rib and a lower rib, the upper and lower ribs traversing the first support member, the first and second support members supporting the transverse member in a substantially-vertical position.

2. The device according to claim 1, wherein the transverse member is composed primarily of a plastic material.

3. The device according to claim 2, wherein the plastic material is rigid and includes polyethylene.

4. The device according to claim 3, wherein the polyethylene has a density greater than a preselected value.

5. The device according to claim l, wherein the transverse member includes a one-piece permeable grid, the grid including the upper and lower ribs.

6. The device according to claim 5, wherein the grid is composed primarily of a plastic material.

7. The device according to claim 6, wherein the plastic material includes polyethylene.

8. The device according to claim 7, wherein the upper and lower ribs are horizontally-oriented and are spaced from one another, at least one horizontally-elongated opening being defined between the upper and lower ribs. 8

9. The device according to claim 8, wherein the grid further includes first and second vertically-oriented junctions, the horizontally-elongated opening being defined between the first and second junctions and the upper and lower ribs.

10. The device according to claim 9, wherein the opening is approximately 6" long and approximately 1" wide.

11. The device according to claim 1, wherein the first and second support members include first and second posts, respectively.

12. The device according to claim 1, wherein the first support member has a first portion and a second portion opposite the first portion, and wherein the upper and lower ribs are weaved around the first support member such that the upper rib traverses the first portion of the first support member and the lower rib traverses the second portion of the first support member.

13. The device according to claim 12, wherein each of the upper and lower ribs is composed primarily of a high- density plastic material.

14. The device according to claim 13, wherein the plastic material includes polyethylene.

15. The device according to claim 14, wherein the first and second support members include first and second steel posts, respectively.

16. The device according to claim 11, wherein the transverse member is supported by the first and second posts without a mechanism to fasten the transverse member to the first and second posts.

17. The device according to claim 1, wherein the device is a sand retention fence.

18. The device according to claim 1, wherein the device is arranged in a zig-zag formation.

19. The device according to claim 1, wherein the device is arranged in a double zig-zag formation.

20. An upland device installed at a toe of a sand dune spaced from a body of water for preventing erosion of the sand dune by the water, comprising: a substantially-vertical first support member installed in a first part of the toe of the dune, the first support member having a first portion and a second portion opposite the first portion; a substantially-vertical second support member installed in a second part of the toe of the dune; and a one-piece polyethylene grid member extending between the first and second support members, the grid member including first and second substantially- horizontal ribs, the first and second ribs traversing the first and second portions, respectively, of the first support member, the first and second support members supporting the grid member in a substantially-vertical position.

21. The device according to claim 20, wherein the grid member further includes at least one substantially- vertical junction extending between the first and second ribs, at least one horizontally-elongated opening being formed between the first and second ribs.

22. A device for positioning upland from a body of water for preventing erosion by the water, comprising: a one-piece, permeable grid, the grid including first and second substantially-horizontal ribs and first and second substantially-vertical junctions, at least one horizontally-elongated opening in the grid being formed by the first and second ribs and the first and second junctions, the grid being composed primarily of a plastic material; a first securing member for securing a first portion of the grid to a first location upland from the body of water; and a second securing member for securing a second portion of the grid to a second location upland from the body of water.

23. The device according to claim 22, wherein the grid is in a substantially-vertical position.

24. The device according to claim 22, wherein the grid is composed entirely of the plastic material, the plastic material including polyethylene.