WO2006120410A1

WO2006120410A1 - Flood barrier

Info

Publication number: WO2006120410A1
Application number: PCT/GB2006/001663
Authority: WO
Inventors: John Robert Greenwood
Original assignee: John Robert Greenwood
Priority date: 2005-05-10
Filing date: 2006-05-08
Publication date: 2006-11-16
Also published as: ATE419432T1; EP1880058A1; GB0509477D0; DE602006004581D1; GB2426026A; EP1880058B1

Abstract

A flood protection or defence barrier for preventing flooding of areas or regions prone to flooding. The barrier comprising a liner (1) for lining an interior of an excavated trench and receiving a backfill from the trench, and at least one rigid pivotable cover (6) coupled to the liner (1) , which rests at or near groud level when not in use. In response to localised flooding, the cover (6) is operable to pivotally rise under the action of a buoyant force, to thereby impede /prevent the flow of flood water passing by the barrier. The invention also relates to a method of installing such a barrier.

Description

FLOOD BARRIER

The present invention relates to flood protection and flood defences for areas and regions liable to flooding, and in particular relates to a flood barrier for protecting land and property and a method of installing such a barrier.

The need to protect land and property from the dangers of flooding have been apparent since earliest times. However, with recent environmental and climatic changes, the frequency of flooding events in populated areas has increased steadify during the last few years. Unexpected flooding is nearly always undesired and usually significant damage to property and/or land results from any such event. T)⁷PiCaIl)', there will be large costs involved in the subsequent clearing up operation by local authorities, as well as both financial and personal loss for those unfortunate individuals who are caught up in such natural disasters.

The authorities responsible for preventing flooding, such as the Environment Agency and local municipal authorities in the UK₅ conventionally use permanent or semi-permanent fixed flood protection walls or bunds, situated close to those sites, such as river banks and shoreline deltas etc., which are particularly vulnerable or liable to flooding at various times of the year. However, a major disadvantage of such walls or bunds is the cost of installation, which can be significant depending on the size of the area or region which is at risk of flooding.

Moreover, it is usual for conventional permanent defences to be physically intrusive on the surrounding landscape and may also be quite unsightly in appearance. Therefore, such defences can significantly detract from an area's aesthetic appeal, particularly in regions of natural beauty, such as in the countryside or along river banks etc.

The costs of permanent defences are especially important to under-developed countries, or third world countries, as the considerable installation costs are usually not viable for such countries. Therefore some of the most vulnerable areas can be left unprotected. This can have significant implications for destruction of crops and homes during flooding events, which can have disastrous effects on the local econoni)' and health of the effected populations.

The present invention is directed to a flood protection or defence barrier which is intended to replace conventional fixed flood protection walls and bunds, while avoiding the physical and aesthetic intrusion of the conventional flood defences on the surrounding environment.

The fabrication and installation of the present barrier is expected to be of relatively lower cost than existing flood defences, and will provide a viable alternative for many flood risk areas and regions of the UK, and in the world in general. In particular, it will provide an attractive low cost solution to local flood risk regions in many third world developing countries etc., while leaving only a marginal 'fingerprint' on the surrounding landscape and environment.

An object of the present invention is to provide a flood defence barrier that can automatically respond to a flood event and prevent the subsequent flow of flood waters passing by the barrier.

A further object of the present invention is to provide a flood defence barrier that can operate under the action of a buoyant force created by the ensuing flood waters.

A further object of the present invention is to provide a flood defence barrier that when not in use has only a minimal fingerprint on the local environment.

According to a first aspect of the present invention there is provided a flood protection barrier including an impermeable flexible membrane entrapped within a backfilled trench and rigid covers which rest at or near ground level and which rises automatically on floats during flood conditions.

According to a second aspect of the present invention there is provided a flood defence barrier, comprising: a liner for lining an interior of a trench, and receiving backfill material to at least partly fill the trench; and at least one pivotable cover coupled to the liner and operable to pivotally rise under the action of a buoyant force in response to a flood event.

According to a third aspect of the present invention there is provided a method of installing a flood defence barrier, comprising the steps of: lining an interior of an excavated trench with a liner; backfilling the liner with backfill material; and coupling at least one pivotable cover to the liner, the cover being operable to pivotall)' rise under the action of a buoyant force in response to a flood event.

Embodiments of the present invention will now be described in detail by way of example and with reference to the accompanying drawings in which: Figure 1 is a side cross-section view of a flood defence barrier according to a preferred arrangement, in a stowed position.

Figure 2 is a side cross-section view of the flood defence barrier of Figure 1 in a deplo}'ed position during a flood event.

Figure 3 is a side cross-section view of a flood defence barrier according to an alternative arrangement, in a deployed position.

Figures 4(a)-4(l) are side cross-section views of a preferred method of installation of a flood defence barrier according to the present invention.

With reference to figure 1 there is shown a particularly preferred arrangement of a flood defence barrier according to the present invention. The barrier is located in areas or regions which are known to be at risk from flooding. In figure 1, the area

(e.g. land and/or property) to be protected is denoted by 10, which for sake of example is relatively higher than the opposing area denoted by 9. In all the figures

1 to 4, flood waters are expected to arrive from the lower area 9 (e.g. from an overflowing river bank or shore) and head towards the higher area 10.

The barrier comprises a liner 1 for lining an interior of an excavated trench, which is located between the area 10 to be protected and the area 9 from which flood waters are to be expected. In preferred arrangements, this liner 1 is formed from a substantially flexible membrane, which is impermeable to flood water. The membrane is preferably a reinforced pofymer material, such as plastic sheeting, or a rubberised matting or else may be a similar hardwearing material.

It is to be appreciated that the length of the membrane is dimensioned to fit the length of the trench, and therefore referring again to figure 1. the membrane can extend into the plane of figure 1 for as long as the trench continues. It has been found that the stability of the barrier of the present invention is optimum when the depth and the width of the trench are approximately equal to each other and equal to the height of the flood water above the top of the trench, as shown in figure 4(a) (this being measured for example relative to the lower area side 9).

Therefore, in preferred arrangements, the width dimension of the membrane is preferably at least 5 times the width d of the trench, so as to cover each of the excavated interior faces of the trench and provide two portions external to the trench, as best shown in figure 4(c). These two external portions will be described in detail below.

It is to be appreciated however, that although a substantially square trench cross- section is preferred for use with the present barrier, other trench cross-sections are consistent with the present invention. Moreover, an advantage of using a flexible membrane liner 1 is that the liner 1 can deform to follow the contours of the trench and therefore any suitable shape trench may be used.

To accommodate variations in the ground surface and/or natural landscape contours, the membrane can be constructed in sections of predetermined lengths, which can be joined together using suitable water tight joints and/or adhesives etc. Alternatively, if a single continuous membrane is used, then regular pleated portions can be incorporated into the membrane to permit the membrane to contort, horizontally and/or vertically, to follow the natural variations of the landscape. To secure or entrap the membrane in place within the trench, the membrane is filled with excavated material 2, i.e. 'backfill', such as soil etc. that originated from the trench. This provides stability for the barrier and also advantageously makes use of the original ground material, thereby avoiding the need to provide building aggregates etc. at the installation site and hence reducing the cost of installation. However, it will be understood that the expression 'backfill' is intended to encompass any suitable material for providing ballast or stability to the barrier, and need not be material excavated from the trench.

Referring again to figure 1, the barrier further comprises at least one pivotable cover 6, which is coupled to the liner 1 and is operable to pivotalry rise under the action of a buoyant force in response to a flood event.

By 'flood event' we mean that flooding has commenced and that at least some initial flood waters have begun to flow across the barrier towards the protected area 10 of land and/or property.

Of course, it is to be appreciated that in practical applications, there would be a plurality of pivotable covers 6, each adjacent to the other and extending along the length of the membrane (i.e. trench), to thereby provide a self-erecting, automatic barrier to the passage of flood water. In preferred arrangements, the width dimension of the cover 6 is substantially the same as the width of the trench, which in the optimum arrangement is the same as the depth of the flood waters. However, the width of the cover 6 can be made slightly larger than the width of the trench, to accommodate any unexpected variances in the depth of the flood water.

In preferred arrangements, the covers 6 are substantially rigid and are. made from any of the following materials: exterior plywood, timber decking, recycled polymer compound or medium density fϊbreboard (MDF). However, it is to be appreciated that the covers 6 can be made from any suitable material, even plastics. Of course, the covers 6 must be hardwearing and strong, to resist the forces of the flood water, and it is preferred that the covers 6 have a degree of internal buoyancy, such that a suitable uplift will arise in response to ensuing flood water.

Moreover, the cover material should ideally be in keeping with the local environment, so as to minimise the visual impact of the barrier on the surrounding landscape. For these reasons, the above example forms of wood are preferred.

The cover 6 is preferably coupled to one of the external portions of the membrane, i.e. the portion of membrane which is located on the trailing edge of the trench. By 'trailing edge' we mean the edge on the side of the trench which is situated adjacent the area 10 to be protected from flooding (see figure 2). Preferably, the cover 6 is coupled to the membrane by way of conventional bolts and washers, either metal or plastic, at points 5 and 14 for example. Alternatively, water-proof adhesives may be used instead.

Preferably most, if not all, of the inner face of the cover 6 (i.e. the flood water facing side) is covered by the trailing edge portion of the membrane. In this way, a more secure and water-tight barrier is achieved along the length of the defence.

Referring to figure 1 again, it can be seen that in preferred arrangements, the cover 6 resides at substantially the level of the ground surface, when in a stowed (i.e. non-flood event) position. By 'level of the ground surface' or 'ground level' etc. we mean the average level of the ground surface immediately adjacent to the barrier.

In this way, the fingerprint or physical extent of the barrier on the local landscape is minimised when there is no flooding, as the only visible part of the defence is the outer face of the stowed cover 6. It is possible to match the colour of the cover 6 to the natural or artificial colour-scheme of the local environment, to thereb)' further reduce the physical intrusion on the surrounding landscape.

As shown in figure 2, the cover 6 responds to a flood event by pivoting at the trailing edge of the trench, by virtue of the coupling to the membrane. In this way, the membrane acts as a hinge device for the covers 6 along the length of the barrier, without the need for any mechanical hinges or additional hinge components.

The maximum height of the cover 6 is a function of the depth of the flood water above the top of the trench, which in most installations is approximately at the level of the surrounding ground. This relationship can most readily be appreciated in figure 2. By 'maximum height of the cover' we mean the height above ground level of the leading edge of the cover 6.

To increase the buoyancy of the cover 6, in some preferred arrangements, a float 7 can be attached to the cover 6 or the membrane, close to the leading edge of the cover. Any suitable float 7 may be used, provided it is capable of uplifting the cover 6 in response to a flood event. Typical examples include fishing floats, boat floats, sealed hollow plastic containers and blocks of polystyrene etc. Of course, the size and effectiveness of the floats 7 will need to be closely matched to the particular application and the dimensions and weights of the associated covers 6.

Preferably, during non-flood events, when the cover 6 is in a stowed position, the float 7 resides beneath the cover 6 and inside a small hollow cavity remaining at the top of the trench. The volume of this cavity can be adjusted by varying the amount of the backfill material, to thereby accommodate varying sizes of float 7, depending on the particular application.

In some arrangements, the float 7 may be attached to the membrane/cover by repeatedly wrapping a portion of the membrane around the float 7, as illustrated in figure 3. This of course, requires the overall width of the membrane to be increased accordingly, so that the external portion on the trailing edge side of the trench has sufficient length to wrap around the float 7.

To avoid the cover 6 from being overturned or flattened by the force of the flood waters when in a deployed position, as shown in figure 2, flexible ties 3 may be attached to the cover 6 to limit the pivotal (or angular) displacement of the cover 6. e.g. at point 5. In a fully deployed position, the cover 6 is preferably substantial^ vertical with respect to the surrounding ground surface, as illustrated approximately in figure 2. Therefore, the length of the tie 3 is selected to permit and limit the displacement of the cover 6 to this substantially vertical position.

Of course, it is to be appreciated that the maximum height of the cover 6 can be set by selecting specific lengths of the tie 3, depending on the particular application and expected depth d of flood water. Therefore, for example, the pivotable cover 6 could be configured to be limited to an angle of approximately 45 degrees with respect to the ground level, if flood waters are not expected to warrant the full deplo3'ment of the cover 6. However, in most practical applications, full deployment (i.e. substantially vertical alignment) is expected to be required, thereby providing maximum protection against ensuing flood waters.

In some alternative arrangements, the flexible tie 3 can be substituted by coupling the leading edge portion of the membrane directly to the cover 6, thereby providing a means of limiting the pivotal displacement of the cover 6 and avoiding the cover 6 overturning during use. In such arrangements the width of the membrane is increased accordingly, so as to provide a wider leading edge portion of the membrane external to the trench. This may then be coupled to an appropriate attachment point (e.g. point 5 in figure 2) on the inner face of the cover 6. To facilitate operation of the cover 6, and avoid undue forces acting on the leading edge portion of the membrane, the portion is perforated with drainage holes across its surface to allow flood water to pass therethrough and to flow against the inner surface of cover 6.

To further improve stability of the barrier, a stabilising structure, such as a concrete block or slab 4, can be placed inside the trench portion of the membrane, directly on top of the backfilled material, as shown in figures 1 and 2. The slab 4 may perform one or more beneficial functions, such as (i) exert compressive forces on the backfill, (ii) resist forces from the tie 3, (iii) provide lateral rigidity across the width of the trench and (iv) generally provide greater stability for the barrier. Of course, any suitable weight, strut or block 4 can be used to impart compressive forces to the backfill material and/or maintain stability of the barrier, including locally sourced materials, such as boulders etc. However, a rigid block 4 is preferred since it can also act as a horizontal strut maintaining dimensional stability of the barrier, e.g. by extending across the width of the barrier.

Should additional stability be required, depending on the particular application, one or more tethered ground anchors 16 may be used. These are preferably inserted into the ground material surrounding the trench during excavation of the trench and are then tethered to the one or more stabilising structures 4, e.g. at point 13 in figures 1 and 2. Any suitable anchoring devices and tethers may be used, but 'duckbill' or 'platypus' style anchors and flexible, high tensile tethers are preferred.

In all arrangements, the membrane, ties 3 and tethered ground anchors 16 may all be attached to one or more stabilising structures 4 within the liner of the trench, so as to provide increased stability of the barrier against the hydraulic forces created by the flood waters. The ties 3 may be extended and connected to the membrane liner 1 near the base of the trench. The connection may be by welding, use of adhesive or by mechanical means. A convenient method is to fold and weld the membrane back on itself incorporating a plastic rod in the fold. A small notch may then be cut locally in the membrane to expose the rod and permit the tie to pass around the rod and be knotted or mechanically fixed back on to itself. The use of the extended tie or perforations in the membrane on the low area side 9 of the trench, will be beneficial in preventing water standing becoming stagnant within the trench lining.

To facilitate the ingress of flood water under the cover 6 during a flood event, the region of ground 8 at the leading edge of the trench is preferably replaced by a high permeability material, such as coarse gravel or aggregate, as shown in figures 1 and 2. By 'high permeability' we mean that the material allows substantially unimpeded flow to flood waters passing through the material. In this way, flood water is allowed to 'seep' under the cover 6 during a flood event, to thereby give rise to a requisite buo3^?ant force required to cause the cover 6 to pivot upwardly and deplo3^r in the face of the ensuing water.

Of course, it is to be appreciated that any suitable means ma}' be used as an alternative to the gravel, such as a metal grate or porous stone etc., depending on the particular application and requirement not to intrude on the aesthetics of the local environment.

Referring to figure 3, there is shown an alternative arrangement of the barrier of ^■ the present invention. In this arrangement, the liner 1 comprises a substantially rigid open-top box structure 17, as a replacement for the trench (or underground) portion of the membrane, and further comprises a flexible membrane portion coupled to the box structure 17. The box structure 17 may be made from any suitable strong, hardwearing material, and preferably is selected from one of the following materials: concrete, brick, plastic polymers and metal. However, in an exemplary arrangement, the box structure is a plastics polymer crate.

In the same manner as the previous arrangements, the box structure 17 is placed inside of an excavated tench, and backfill material is placed inside the box structure 17 for stability. Depending on the particular rigidity of the box structure 17, additional stabilising structures or blocks 4 may or may not be required, as the box structure itself may be able to provide sufficient stability against the forces of the ensuing flood water. In figure 3, additional stabilising structures are not shown for clarity.

To permit ingress of flood water under the cover 6, via the coarse gravel region 8, access holes or bores 19 are included at the leading edge of the box structure, as shown in figure 3.

The flexible membrane portion is coupled to the box structure 17 at point 20, using any suitable means, including nuts and bolts and water-proof adhesives etc. As before, the membrane portion is arranged to cover the inside surface of the cover 6, and as shown in figure 3, may be sufficient in width to wrap around a float 7. if fitted. The flexible membrane portion my act as a binge device for the cover 6, or alternatively, the cover 6 can be attached directly to the box structure using any suitable mechanical hinge 22.

The box structure 17 can be made in any length and need not be linear in form. Hence, the box structure may be fabricated in arcuate sections, as appropriate, so as to follow natural contours and features within the landscape of installation. However, in preferred applications, the box structure 17 is rectangular in form and is arranged to be modular, so that each box structure 17 can be connected to one or more adjacent box structures within the trench, each having at least one pivotable cover 6.

Preferably, the box structures 17 are connected by way of linking bolts 21, which may be pre-fabricated on the side walls 18 of the structure, and which are received by reciprocal sockets on the side walls of adjacent box structures 17. Alternatively, the side walls of adjacent box structures may be drilled in situ and bolted together, as appropriate, at the site of installation.

It is also possible that the box structures could have side walls which are fabricated with reciprocal 'tongue and groove' members, which permit adjacent box structures to be slotted together, again in situ.

In all arrangements, concrete or any suitable hardwearing material, e.g. asphalt or tarmac etc., may be placed on the ground at either side of the trench, to provide greater stability and, if necessary, to provide additional load bearing support for the cover 6 when in a stowed position. This latter feature can be useful where the barrier is to be deployed in regions where vehicle traffic is expected to pass over the barrier, so that the covers 6 are better supported when bearing a load. In such arrangements, the covers 6 can be made wider than the width of the trench, so that the peripheral edge portions of the cover reside on the concrete or asphalt supports. Referring to figures 4(a) to 4(1), there is shown a sequence of steps in a particularly preferred flood barrier installation method according to the present invention. This sequence of figures relates to installation of a continuous, flexible membrane liner 1 as discussed in earlier arrangements. However, many of the steps are equally applicable to box structure liner arrangements, requiring only minor changes in installation, and therefore the illustrated steps are not intended to be limiting.

In figure 4(a), a schematic side view of the identified flood barrier site is shown, together with the depth d of the flood water expected to arise when a flood event occurs in this area. In typical arrangements, as discussed previously, the optimum arrangement for the barrier is to use a trench that has a width and depth approximately equal to the depth of the flood waters. Therefore, as shown, the trench width = trench depth = depth of flood water d. This arrangement provides a suitably stable and reliable configuration for the barrier.

Once the site of the barrier is identified, by way of geological surveying and/or previous flooding records etc., mechanical diggers, or manual labour, can be used to excavate a suitably dimensioned trench, as shown in figure 4(b), with the backfill from the trench being retained.

In figure 4(c), the step of lining the interior of the excavated trench with a liner 1, e.g. flexible membrane, is completed. Depending on the particular application, the width of the membrane is preferably selected to provide overlapping portions Ia, Ib of the membrane (i.e. external to the trench) which are at least d metres in width, on either side of the trench. These portions Ia, Ib were referred to previously as the leading and trailing edge portions of the membrane. If it is desired to use the leading edge membrane portion Ib as a replacement for tie 3, then this portion should have a width greater than d, to permit appropriate pivotal displacement of the cover 6 during use.

Hence, it can be seen in figure 4(c) that for a square cross-section trench, the width of the membrane would need to be at least 5 times the width of the trench. For stability, the trench portion of the liner 1 is then backfilled with excavated material 2, as shown in figure 4(d). Most, if not all, of the backfill material 2 may be used. However, a small cavity or volume at the top of the trench should be retained, to permit storage of the float 7 and ties 3 when the cover 6 is in a stowed position, i.e. during non-flood events.

As shown in figure 4(e), a stabilising structure 4, such as a concrete slab or block 4, may optionally be placed on top of the backfilled material 2, to compress and compact the material and/or provide greater stability for the barrier.

Once the membrane is entrapped by the backfilled material, at least one pivotable cover 6 is coupled to the liner, as shown in figure 4(f), using bolts or adhesive etc. In the example shown, the cover 6 is coupled to the trailing edge portion of the membrane Ia.

Optionally, depending on the particular application and size and weight of the cover 6, a float 7 may be attached to the coλ'er 6 as shown in figure 4(g).

At the same time, one or more ties 3 may be connected to the cover 6 to limit the pivotal displacement of the cover during deployment. Alternatively, the leading portion of the membrane can be folded back and connected directly to the cover 6, as a replacement for one or more of the ties, as shown in figure 4(h).

Although not illustrated in figure 4, tethered ground anchors 16 may also optionally be attached to the stabilising structure 4 at this time, having previously been inserted into the ground following excavation of the trench.

In figure 4(i), the barrier is then checked by stowing the cover 6 and verifying that all components are aligned correctly etc, and that the cover 6 rests unobtrusively at or near ground level. As a final step, the ground adjacent to the leading edge of the trench may be replaced by high permeability material, such as coarse gravel 8, as shown in figure 4Q).

In figures 4(k) and 4(1), the flood barrier is shown in both deployed and stowed positions respectively. In figure 4(k), a flood event has given rise to flood water which has caused the cover 6 to pivotally rise and thereby prevent the flow of flood water beyond the barrier and towards the protected area 10. When the flood water subsequently subsides, the cover 6 gradually falls under the action of its own weight (and that of the float 7 if fitted) until it once more assumes a stowed position, at or near to ground level, thereby minimising the visual intrusion on the local landscape, as shown in figure 4(1).

Although in previous arrangements, it has been discussed that the flood barrier is preferably installed at ground level, there are some applications in which installation of the barrier at a position slightly above ground level can be advantageous. In particular, in regions where tsunami type wave fronts or tidal waves occur, i.e. unexpected uprisings in the level of the local water table. In these applications, the present barrier can be positioned at a relatively raised level to the surrounding ground, so as to provide a more rapid response to the surging flood water. Of course, this does have the effect of intruding more on the local environment, however for such regions the greater protection afforded against surging flood water is deemed to be appropriate compensation for any possible detrimental effect on the aesthetic appearance of the immediate area.

In such arrangements, the impact forces of the surging flood water on the covers 6 can be absorbed by including one or more shock absorbing devices, preferably comprised of lengths of resilient material attached to the flexible ties 3, which come into effect when the covers 6 reach a substantially vertical position, i.e. when they are fully deployed.

Although the flood defence barrier of the present invention is ideal for preventing flooding in flood risk areas and regions, it will be recognised that one or more of the principles can extend to other applications, including containing hazardous liquid spills and leakages, and anywhere where temporary water storage is required, e.g. in flood lagoons, balancing ponds, temporary reservoirs etc. It will be understood that the expression 'flood protection barrier' is intended to encompass all forms of fluid containment barriers whether used to contain accidental or deliberate flooding of an area. The barrier as described herein can also be used to supplement existing flood barriers, e.g. by construction of the barrier on top of an existing flood defence such as a levee.

Other embodiments are taken to be within the scope of the accompanying claims.

Claims

1. A flood protection barrier including an impermeable flexible membrane entrapped within a backfilled trench and rigid covers which rest at or near ground level and which rises automatically on floats during flood conditions.

2. A barrier as claimed in claim 1 where stability is maintained by flexible ties, which ma}' be an extension of the membrane in claim I₅ entrapped in a backfilled trench.

3. A barrier as claimed in claim 1 or claim 2 where stability is maintained by ground anchors attached to the barrier by flexible ties.

4. A barrier as claimed in any preceding claim where stability is maintained by the membrane, flexible ties and ground anchor ties attached to a slab of concrete or suitable material within a backfilled trench.

5. A barrier as claimed in any preceding claim where stability is maintained by the membrane, covers, flexible ties and ground anchor ties attached to box structures of concrete, polymer or suitable material in a backfilled trench.

6. A barrier as claimed in any preceding claim which when not in use rests unobtrusively at or near ground level protected by covers of suitable material.

7. A barrier as claimed in any preceding claim and having concrete or other substantial edges to the backfilled trench to support the covers in the event of traffic or other loading.

8. A barrier as described in any preceding claim and positioned when not in use slightly above ground level to provide faster response of the floats to a tidal wave or tsunami.

9. A barrier as described in any preceding claim where wave impact forces are absorbed by shock absorbers which may be of resilient material attached to the flexible ties or other suitable form.

10. A flood barrier substantial!}' as herein described above and illustrated in the accompanying drawings.

11. A flood defence barrier, comprising: a liner for lining an interior of a trench and receiving backfill material to at least parti}' fill the trench; and at least one pivotable cover coupled to the liner and operable to pivotally rise under the action of a buoyant force in response to a flood event.

12. The flood defence barrier of claim 11, wherein the liner is made of a substantially flexible membrane .

13. The flood defence barrier of claim 12, wherein a portion of the inner face of the cover is covered by the membrane.

14. The flood defence barrier of claim 11, wherein the width dimension of the cover is substantially the same as the width of the trench.

15. The flood defence barrier of claim 11, wherein the width dimension of the liner is at least 5 times the width of the trench.

16. The flood defence barrier of claim 11, wherein, in use, the maximum height of the cover is a function of the height of the flood water above the top of the trench.

17. The flood defence barrier of claim 11, wherein the liner comprises a substantially rigid open-top box structure.

18. The flood defence barrier of claim 17, wherein the box structure is made of any of the following materials: concrete, brick, plastic polymers and metal.

19. The flood defence barrier of claim 17 or claim 18, wherein the liner further comprises a flexible membrane portion coupled to the box structure.

20. The flood defence barrier of any of claims 17 to 19, wherein the box structure is modular and configured to be connected to one or more adjacent box structures within the trench, each having at least one pivotable cover.

21. The flood defence barrier of any of claims 11 to 20, further comprising a float for attaching to the cover.

22. The flood defence barrier of any of claims 11 to 21, further comprising a stabilising structure extending across the top of the backfill material within the liner to stabilise the barrier.

23. The flood defence barrier of any of claims 11 to 22, further comprising at least one tie attached to the cover for limiting the pivotal displacement of the cover.

24. The flood defence barrier of claim 23, wherein the tie is associated with one or more shock absorbing devices to reduce the effects of flood water forces acting on the cover.

25. The flood defence barrier of any of claims 11 to 24, further comprising at least one tethered anchor for stabilising the barrier.

26. The flood defence barrier of any of claims 11 to 25, further comprising a high permeability material for disposing substantially at a leading edge of the trench to permit the ingress of flood water under the cover during use.

27. A method of installing a flood defence barrier, comprising the steps of: lining an interior of an excavated trench with a liner; backfilling the liner with backfill material; and coupling at least one pivotable cover to the liner, the cover being operable to pivotalfy rise under the action of a buoyant force in response to a flood event.

28. The method of claim 27, further comprising the step of: placing a stabilising structure extending across the backfill material within the liner to stabilise the barrier.

29. The method of claim 28, further comprising the steps of: attaching a float to the cover; attaching at least one tie to the cover for limiting the pivotal displacement of the cover; and attaching a tethered anchor to the stabilising structure for stabilising the barrier.

30. The method of any of claims 27 to 29, further comprising the step of: disposing a high permeability material at a leading edge of the trench to permit the ingress of flood waters under the cover during use.