GB2373280A

GB2373280A - Block for seashore erosion protection

Info

Publication number: GB2373280A
Application number: GB0106715A
Authority: GB
Inventors: Reginald Slack
Original assignee: SEA DEFENCES Ltd
Current assignee: SEA DEFENCES Ltd
Priority date: 2001-03-16
Filing date: 2001-03-16
Publication date: 2002-09-18
Anticipated expiration: 2021-03-16
Also published as: GB0106715D0; GB2373280B

Abstract

An erosion prevention structure comprises a number of large blocks 1 interconnected and arranged along a beach 14, Fig 2) to be protected, each block has a sloping top side which rises from a front edge to an up-beach lip 2 which is shaped to collect beach material (15, Fig 2) behind it. The blocks may be made of concrete and may be generally cubic in shape with a flat top surface 9 and a curved lip 10 extending up from the back edge of said top surface. The sides of the blocks may have complementary dovetail formations 7 and 8 such that a number of the blocks can be interconnected to form the structure. Two or more lines of the blocks may be arranged across a beach with interconnection blocks (21, Fig 3) provided to link the lines.

Description

GROYNE The present invention relates to a groyne Generally groynes are positioned up and down a beach, in the direction of rise and fall of the tide, with the objective of interrupting tidal movement of beach material-for example shingle and gravel-along the beach due to tidal flow along the beach, such flow typically being stronger at the beach in one direction than the other. The interruption of movement results in deposition of the material on the up tide side of the groyne. The result is that the beach is higher to one side of the groyne than the other.

Tidal flow along a beach is an order of magnitude less than the speed of waves up and down beach. The most movement at any one time is of material being washed up and down the beach by waves breaking on and washing the beach and then flow back down.

Sea defences are positioned at the top of a beach, along its length, or along a sea front at positions where the tide does not ebb far enough to expose a beach. They are high and substantial whereby normal wave action does not wash beach material over the top of them.

The object of the present invention is to provide a groyne of an unconventional nature that can be arranged along a beach to take advantage of meach material being washed up the beach, trapping it and thereby augmenting the beach.

According to the invention there is provided a groyne comprised of a series of massive blocks interconnected and arranged along a beach, the blocks being arranged with a sloping top side rising to an up-beach lip arranged for beach material to accumulate behind.

Typically the blocks will be of concrete.

It is envisaged that the blocks could have upright front and back sides, with the back side being taller than the front side in accordance with the sloping top side However, the blocks are preferably configured such that the up-beach lip extends from backside. Where the top of the main body of the block is flat and the lip extends up from the back side, the cross-sectional shape of the groyne is generally similar to the side view of a saucepan with the lip representing the handle.

To help understanding of the invention, a specific embodiment thereof will now be described by way of example and with reference to the accompanying drawings, in which : Figure 1 is a perspective view of a single concrete block of the invention; Figure 2 is cross-sectional side view of a three lines of block s as in Figure 1 set in a beach; Figure 3 is a perspective view of three lines of blocks set in a beach.

Referring to first to Figure 1, the individual block 1 thereshown has a generally cubic shape with a substantial lip 2 extending from one side 3, referred to as the back side, because in use the opposite front side 4 faces the sea The sides 5,6 extending between the front and back sides have complementary dovetail formations 7,8, where a number of the blocks can be connected in line. The top surface 9 of the block is generally flat, above the main body of the block within the sides 3,4, 5,6 The lip is angled up at a slight angle-typically 15 , but chosen to suit the beach in question where the groyne is to be installed. The top surface of the lip curves smoothly from the flat top of the main body. The edge 10 of the lip is angled sharply down to provide a face against which beach material can accumulate. Typically, the bodies of the blocks will be of the cubic with dimension of the order of 1. 25m and a volume of approximately 2m3, and weigh of the order of the order of 4.5 to 5 0 tonnes. Such a block can have a front side 4 to back edge 8 dimension of 1.85m and a corresponding height rise of 0 30 metres. This corresponds to a beach gradient of 1 in 6. This is a steep gradient and blocks can be made shallower for shallower beach gradients.

As shown in Figures 2 & 3, the block are connected together in lines 11,12, 13 forming groynes along the beach, each groyne being spaced apart from the next up

and down the beach. In this respect, these Figures are exaggerated in showing close I spacing of the lines. The blocks are positioned originally with upto one half of their extent exposed above the original beach surface 14. As shown, those further up the beach are installed more proud than those lower down the beach As the waves washes against the groynes, beach material is washed over them and becomes trapped 15 behind them As the material becomes progressively deposited behind the first groyne, it will be at a height to be washed by wave action over the next groyne. Thus the entire beach to landward of the groynes can be expected to build up to a new level 16.

It is expected that the groynes will be set out closer to the low tide mark than the high tide mark to gain benefit over more of the beach. In particular where the beach is backed by an eroding cliff, the groynes would be set away from the foot of the cliff, to allow the beach to aggregate at the foot of the cliff to restrict washing of the foot of the cliff at high tide.

The invention is not intended to be restricted to the details of the above described embodiment. For instance on beaches where there is a strong tide along the beach, the lines of groyne blocks may be interconnected by periodic interconnection blocks 21 as shown in outline in Figure 3 Each end 22,23 of these essentially comprises one of the blocks, fitting into the extent of the longitudinal groyne and an interconnection run 24 Where the interconnection run would extend too far up the beach to be able to be made as one length, it may be subdivided into pieces themselves connected by dovetail joints. The interconnection blocks are set at the height of the expected new level 16 of the beach to stabilise it between the longitudinal groynes, that is avoid the new level being washed out along the beach

Claims

CLAIMS : 1. A groyne comprised of a line of massive blocks interconnected and arranged along a beach, the blocks being arranged with a sloping top side rising to an up-beach lip arranged for beach material to accumulate behind.
2. A groyne as claimed in claim 1, wherein the blocks are of concrete.
3. A groyne as claimed in claim 1 or claim 2, wherein the blocks have upright front and back sides, with the back side being taller than the front side in accordance with the sloping top side.
4. A groyne as claimed in claim 1 or claim 2, wherein the blocks are configured such that the up-beach lip extends from the back side.
5. A groyne as claimed in claim 4, wherein the top of the main body of the blocks is flat and the lip extends up from the back side.
6. A groyne as claimed in claim 5, wherein the cross-sectional shape of the groyne is generally similar to the side view of a saucepan with the lip representing the handle.
7. A groyne as claimed in any one of claims 4 to 6, wherein the top surface of the lip curves smoothly from the flat top of the main body.
8. A groyne as claimed in any one of claims 4 to 7, wherein the lip is angled up at a slight angle.
9. A groyne as claimed in any one of claims 4 to 9, wherein the distal edge of the lip is angled sharply down to provide a face against which beach material can accumulate.
10. A groyne as claimed in any one of claims 4 to 10, wherein the distal edge of the lip is rounded.
11. A groyne as claimed in any preceding claim, wherein the sides of the blocks intermediate the front sides and the back sides have complementary dovetail formations by means of which a number of blocks are interconnected in line to form the groyne.
12. A groyne as claimed in any preceding claim, wherein the blocks are of generally cubic shape.
13. A groyne as claimed in any preceding claim, comprising two or more lines of blocks, the lines being interconnected by periodic interconnection blocks.
14. A groyne substantially as hereinbefore described with reference to the accompanying drawings.
15. A block for the groyne as claimed in any one of the preceding claims.