GB2425559A

GB2425559A - Pivoting flood defence apparatus

Info

Publication number: GB2425559A
Application number: GB0605074A
Authority: GB
Inventors: Ronnie Falconer
Original assignee: Jacobs UK Ltd
Current assignee: Jacobs UK Ltd
Priority date: 2005-04-27
Filing date: 2006-03-14
Publication date: 2006-11-01
Anticipated expiration: 2026-03-14
Also published as: GB0605074D0; GB2425559B; GB0508502D0

Abstract

A flood defence apparatus (10) comprises a support structure (14), such as a retaining wall or flood wall, and one or more tiltable wall units (12) hingedly attached about a pivot axis to the top of the support structure. Each wall unit has a buoyant water retaining lever arm (20) and a counterweighted abutment lever arm (21) arranged on opposite sides of the pivot axis. The support structure (10) is provided with abutment means (34) which abuts against the abutment lever arm (21) to hold the wall unit in a raised position when the water retaining wall is subject to hydrostatic pressure on its water facing side. In the raised position the water retaining lever arm (20) extends substantially upwards, thereby increasing the effective height of the retaining wall or flood wall (14). The water retaining lever arm (20) may be retracted by tipping back to the lowered position after the risk of flooding has passed.

Description

1 Tipping Flood Defence Apparatus 3 This invention relates to flood

defence apparatus 4 which can be installed in areas prone to flooding and is in a lowered position in normal use, but 6 which can be deployed by tipping to a raised 7 position to contain high water levels in the event 8 of flooding. In particular the invention relates to 9 flood defence apparatus which can be deployed by tipping from a lowered position to a raised position 11 in which the apparatus forms a flood wall, and which 12 can be retracted by tipping back to the lowered 13 position after the risk of flooding has passed.

In fluvial and estuarine situations the adoption of 16 fixed flood defences, such as walls or embankments, 17 as a means of reducing flood risk can often disrupt 18 the visual amenity of an area particularly when 19 these defences are higher than about one metre.

With flood defence schemes, particularly in urban 21 areas, it is usual to seek to achieve environmental 22 enhancement of the area and avoid structures that 1 detract from the visual amenity. There is therefore 2 a requirement for a robust flood defence apparatus 3 which does not detract from the visual amenity but 4 which can be deployed quickly and easily to provide flood protection when the flood conditions require 6 it.

8 According to a first aspect of the present invention 9 there is provided a flood defence apparatus comprising a support structure and at least one 11 tiltable wall unit hingedly attached about a pivot 12 axis to the support structure, wherein each wall 13 unit comprises a water retaining lever arm and an 14 abutment lever arm arranged on opposite sides of the pivot axis, and wherein the support structure is 16 provided with abutment means adapted to abut against 17 the abutment lever arm to hold the wall unit in a 18 raised position in which the water retaining lever 19 arm extends substantially upwards when the water retaining wall is subject to hydrostatic pressure on 21 its water facing side.

23 Preferably the support structure comprises a 24 permanent retaining wall, most preferably a flood retaining wall. The support structure may be of 26 mass concrete, reinforced concrete, steel, alloy, a 27 mixture of any of these or any other suitable 28 material.

Preferably the pivot axis extends close to the 31 centre of gravity of the wall unit. Preferably the 32 wall unit includes a counterweight arranged on the 1 abutment lever arm. The counterweight is thus on 2 the opposite side of the pivot axis to the water 3 retaining lever arm. Preferably the counterweight 4 and pivot axis are arranged such that under the action of gravity alone the wall unit is urged 6 towards a lowered position.

8 Preferably the abutment means comprises a structural 9 element of the support structure provided below the hinge. Preferably the abutment means includes an 11 abutment surface adapted to engage sealingly with a 12 corresponding abutment surface on the abutment lever 13 arm. The abutment means may include a sealing 14 means, such as a sealing strip.

16 The wall unit may include one or more buoyant 17 portions in or adjacent to the water retaining lever 18 arm. Preferably the buoyant portions are arranged 19 such that rising water urges the wall unit to the raised position.

22 Preferably the apparatus comprises a plurality of 23 tiltable wall units hingedly attached to the support 24 structure arranged to form a continuous wall when in the raised position. Preferably the wall units 26 comprise first units and second units arranged 27 alternately, such that a first unit is adjacent to 28 two second units. Preferably the first units are 29 adapted to be raised first and are provided with laterally extending flanges against which the second 31 units can seal, while the second units are adapted 32 to be raised after the first units have been raised.

1 Preferably the laterally extending flanges are 2 provided with sealing slots or other sealing means.

3 Preferably the lateral edges of the second units are 4 provided with corresponding sealing means adapted to sealingly engage with the sealing slots or other 6 sealing means of the first units.

8 Preferably the lateral edges of the water retaining 9 lever arms are provided with slots adapted to accommodate a stop log or other suitable means of 11 sealing a gap between two units if a unit between 12 the two units fails to be raised.

14 In one embodiment of the invention the water retaining lever arm is provided with a traffic 16 bearing surface on its side opposite to its water 17 facing side. In use the traffic bearing surface may 18 be used as a road, walkway or path when the wall 19 unit is in its lowered position. Preferably the outer edge of the water retaining lever arm is 21 provided with a barrier means adjacent to the 22 traffic bearing surface. The barrier means may be a 23 fence, guardrail, handrail or the like. The barrier 24 means may be fixed, demountable or capable of dropping to a lowered position when the water 26 retaining lever arm is in the raised position.

28 Preferably the support structure includes a recess 29 adapted to house the abutment lever arm and/or counterweight in both the raised and lowered 31 positions. Preferably the recess includes a 32 drainage channel. Preferably the support structure 1 includes a curtain wall adapted to prevent access to 2 the underside of the wall unit while the wall unit 3 is in the lowered position. Preferably the curtain 4 wall includes a cover portion adapted to prevent access to the recess and/or to cover the abutment 6 lever arm while the wall unit is in the lowered 7 position. Optionally the cover portion may include 8 secondary abutment means adapted to abut against the 9 wall unit to hold it in a raised position in which the water retaining lever arm extends substantially 11 upwards when the water retaining wall is subject to 12 hydrostatic pressure on its water facing side.

14 Optionally the apparatus may include actuation means operable to raise the wall unit from the lowered 16 position towards the raised position.

18 Optionally the apparatus may include releasable 19 locking means to hold the wall unit in the lowered position.

22 Optionally the apparatus may include releasable 23 locking means to hold the wall unit in the raised 24 position.

26 Preferably the wall unit is of steel, alloy, 27 reinforced concrete, a mixture of these or any other 28 suitable material. The buoyant portions may be 29 voids or inserts of lightweight material. The counterweight may be of reinforced or mass concrete, 31 steel or any other suitable material.

1 In another embodiment of the invention the water 2 retaining lever arm is in the form of a cope.

3 Preferably the support structure is a flood wall.

Preferably the cope is adapted to provide an 6 effective increase in height of the flood wall when 7 the wall unit is in the raised position. Preferably 8 the abutment means is provided at the rear of the 9 flood wall. Preferably the front of the flood wall is provided with a seating means adapted to support 11 the wall unit when it is in the lowered position.

13 Preferably the wall unit is of steel, aluminium, 14 polypropylene, glass reinforced plastic or other

suitable material.

17 Examples of the invention, which are not limiting, 18 will now be described with reference to the 19 following drawings in which: 21 Fig. 1 shows a sectional view through a unit of a 22 flood defence apparatus of the invention according 23 to a first embodiment; Fig. 2 shows a partial sectional view to an enlarged 26 scale through the counterbalance of the flood 27 defence apparatus of Fig. 1 in the raised position; 29 Fig. 3 shows a sectional plan view 111-111 of a number of adjacent units of the flood defence 31 apparatus of Fig. 1 in the raised position; 1 Fig. 4 shows a partial plan view to an enlarged 2 scale of the flood defence apparatus of Fig. 3; 4 Fig. 5 shows a sectional view of another embodiment of a flood defence apparatus of the invention; 7 Fig. 6 shows a sectional view of a further 8 embodiment of a flood defence apparatus of the 9 invention; 11 Fig. 7 shows a sectional view of yet another 12 embodiment of a flood defence apparatus of the 13 invention; and Fig. 8 shows a front elevational view Vill-VIlI of 16 the flood defence apparatus of Fig. 7.

18 With reference to Figs. 1 to 4 there is shown a body 19 of water 2 and a flood defence apparatus 10 comprising a number of tiltable wall units 12 which 21 are each attached to a support structure 14 by a 22 hinge bearing assembly 16. The body of water 2 may 23 be a water course, river, lake, estuary, coastal 24 water or any other body of water, and may not be permanently carrying water. The tiltable wall unit 26 12 is shown in the lowered position in Fig. 1, with 27 intermediate and raised positions of the wall unit 28 12 indicated by the reference numerals 12' and 12'' 29 respectively. In the lowered position the upper surface of the wall unit forms a light traffic 31 bearing surface such as a walkway 18. A guard rail 1 or hand rail 19 may be provided at the outer edge of 2 the walkway 18.

4 The wall unit 12 includes a water retaining lever arm 20 extending to the right of the hinge 16 in 6 Fig. 1, and an abutment lever arm 21 extending to 7 the left of the hinge 16, on which is arranged a 8 counterweight 22. The wall unit can tip about a 9 pivot axis 24 extending through the hinge 16. The counterweight 22 is arranged so that in an 11 equilibrium state with no buoyancy forces the 12 overturning moment from the water retaining lever 13 arm 20 is greater than that from the abutment lever 14 arm 21 and counterweight 22 so that the wall unit remains in the lowered position, even if load from a 16 pedestrian or vehicle is applied to the portion of 17 the walkway to the left of the hinge 16.

18 Alternatively a locking mechanism (not shown) may be 19 installed to secure the wall unit in the lowered position until such time as water levels rise to a 21 predetermined level. At this time the locking 22 mechanism may be released automatically, manually or 23 remotely. Simultaneously an audible or visual 24 warning of the impending operation of the flood defence apparatus may be provided to persons in the 26 vicinity of the flood defence apparatus.

28 The support structure 14 comprises a retaining wall, 29 constructed either as a stand-alone retaining wall or behind or above an existing retaining wall 26.

31 The support structure 14 may be of mass or 32 reinforced concrete, steel or other construction.

1 The existing retaining wall may typically be of 2 masonry, but may be of any construction. The 3 support structure includes a recess 28 which can 4 accommodate the abutment lever arm 21 as the wall unit 12 tilts to the raised position 12''. A 6 drainage channel 30 extends along the recess 28 and 7 takes any water leaking past the raised wall unit 12 8 to a pumping station (not shown) or water holding 9 area (not shown) . The recess 28 is bounded by a curtain wall 32 which extends to the finished ground 11 level adjacent to the traffic bearing surface 18 of 12 the wall unit 12 and which prevents access to the 13 recess 28 while the wall unit 12 is in the lowered 14 position.

16 The support structure 14 includes a structural 17 element 34 extending adjacent to the recess 28. The 18 structural element 34 in the illustrated example is 19 a wall which includes a sloping surface 36 which serves as an abutment means to support the wall unit 21 12 in the raised position, by abutting against the 22 abutment lever arm 21. As can be seen in Fig. 2 23 sealing means, such as compressible rubber "0" ring 24 sealing strips 38, are fixed to the structural element 34 to provide a substantially watertight 26 seal between the support structure 14 and the wall 27 unit 12 when the wall unit 12 is in the raised 28 position. In this position the hydrostatic pressure 29 of the water urges the wall unit 12 to pivot in a counter-clockwise direction, such that the abutment 31 lever arm 21 is urged to compress the sealing strips 32 38.

2 When the wall unit 12 is in the lowered position it 3 rests on a seat 39 provided on the support structure 4 14.

6 The wall unit may be provided with a locking member 7 40 at the end of its abutment or counterweight lever 8 arm 21. The locking member includes a detent 9 portion 42 which is biased by a sprung hinge 44 so that it engages with a nosing 46 of steel or other 11 suitable material when the wall unit 12 reaches the 12 raised position. A release mechanism, for example a 13 cable 48 leading to a manual release handle or lever 14 (not shown) or any other suitable mechanism, may be operated to release the locking member 40 so that 16 the wall units 12 may be lowered manually once the 17 risk of flooding has passed.

19 The wall unit 10 is typically fabricated from mild steel, aluminium, plastic, lightweight concrete, 21 composite construction or the like. The water 22 retaining lever arm 20 includes positive buoyancy, 23 such as hollow cavities, foamed plastic or the like, 24 so that as the water level adjacent to the apparatus 10 rises, buoyancy forces urge the water retaining 26 lever arm 20 upwards. To this end a downwardly 27 projecting buoyant nose portion 60 is provided at 28 the free end of the water retaining lever arm 20, 50 29 that the buoyancy forces start to act before the water level reaches the top of the structural 31 element 34. However it is to be understood that if 32 required the wall unit 12 can be raised manually or 1 by means of an actuator such as the optional 2 hydraulic ram 41. The ram 41 acts between the 3 support structure 14 and the water retaining lever 4 arm 20 and i.n its extended position 41'' holds the wall unit 12 in the raised position.

7 As can be seen in the plan views of Figs. 3 and 4 8 the flood defence apparatus 10 comprises a plurality 9 of Liltable wall units 12 hingedly attached to the support structure 14 arranged to form a continuous 11 wall when in the raised position. There are two 12 types of wall unit, first 12A and second 12B units.

13 First units 12A and second units 12B are arranged 14 alternately, such that a first unit 12A is adjacent to two second units l2B. When the wall is raised 16 the first units 12A are raised first. The water 17 retaining lever arms of the first units 12A have 18 laterally extending flanges 50 against which 19 laterally extending flanges 52 on the water retaining lever arms of the second units 12B can 21 seal when the second units 12B are raised. As can 22 be seen in Fig. 4 sealing means, such as 23 compressible rubber "0" ring sealing strips 54, are 24 fixed to the flanges 54 of the first Units 12A to provide a substantially watertight seal between the 26 first and second units 12A, 12B when the wall units 27 are in the raised position.

29 The lateral edges 56 of the water retaining lever arms 20 are provided with slots 58 adapted to 31 accorrimodate a stop log (not shown) or other similar 32 device, in a known manner, so that stop logs or 1 other devices can be used to bridge between two non- 2 adjacent units in the event that a unit is damaged 3 or cannot be raised.

In the normal' lowered position the apparatus of 6 the invention minimises disruption to views of the 7 environment of the body of water 2 from the area to 8 be protected. Once the flood defence apparatus 10 9 has automatically risen to its raised position during the onset of a flood or extreme high tide or 11 water level it provides the same degree of flood 12 protection that a fixed flood defence of equivalent 13 height (in its raised position) would provide.

The support structure 14 may be constructed at the 16 top of an existing training wall or revetment, or 17 even the top of an existing flood wall. In the 18 lowered position the water retaining lever arm 20 19 cantilevers out over the body of water 2 or its adjacent area and lies at some height above the 21 normal water level 2A.

23 At the onset of a flood or extreme high tide or 24 water level, as the water level 2 rises up to and above the level of the nose portion 60 the buoyancy 26 of the nose starts to raise the water retaining 27 lever arm 20 until a point is reached when the whole 28 wall unit 12 automatically tips up to the raised 29 position and remains in that position until such time as the water level has subsided.

1 It is not essential that a completely watertight 2 seal be obtained between adjacent units 12A, l2B.

3 Any excess leakage can be drained via the drainage 4 channel 30 to a sump (not shown) and if necessary pumped back to the body of water 2.

7 After a flood or extreme high tide or water level 8 event the units 12 are returned to the lowered 9 position manually. In practice operational conditions may be such that the total length of a 11 series of units may be limited, with a short length 12 of fixed flood defence wall between each series of 13 units provided if necessary.

The flood defence apparatus shown in Figs. 1 to 4 is 16 capable of providing a flood defence structure up to 17 a level 30 around 3m high above the existing general 18 landward ground level 3A during high water 19 conditions. This is achieved by providing an additional approximately 2m high water retaining 21 structure over and above the level 3B of protection 22 provided by the structure in the lowered Position 23 which may be approximately lm high above ground 24 level. The dimensions are indicative only. Figs. 5 and 6 show alternative arrangements capable of the 26 same order of protection.

28 Referring to Fig. 5, there is shown a body of water 29 2, such as a river, lake, estuary, coastal water or the like, and a flood defence apparatus 110 31 comprising a number of tiltable wall units 112 which 32 are each attached to a support structure 114 by a 1 hinge bearing assembly 116. The tiltable wall unit 2 112 is shown in the lowered position in Fig. 5, with 3 intermediate and raised positions of the wall unit 4 112 indicated by the reference numerals 112' and 112'' respectively. Where elements of the apparatus 6 are similar to the embodiment illustrated in Figs. 1 7 to 4 these are indicated with the same reference 8 numeral and are not described further.

The wall unit 112 is fabricated from mild steel or 11 aluminium U sections and plate or other suitable 12 material, and has a concrete counterweight 22. The 13 curtain wall 132 includes a cantilever portion 133 14 which projects over the counterweight arm when the unit is in the lowered position, thereby avoiding 16 the danger of debris entering the recess 28 or 17 accidental operation of the wall unit by traffic 18 loads. In this embodiment a locking mechanism to 19 hold the wall unit 112 in the lowered position is not essential. The cantilever portion 133 can also 21 serve as a kerb for the walkway 18. The support 22 structure 114 includes an enlarged seat 39 which 23 supports the water retaining lever arm 20 when the 24 unit is in the lowered position. it is to be understood that this arrangement could be also 26 adopted with the embodiment of Figs. 1 to 4.

27 Additional buoyancy may be provided by a tank 62 of 28 fibreglass, plastic or other suitable material 29 fastened to the underside of the water retaining lever arm 20.

1 Referring to Fig. 6, there is shown a flood defence 2 apparatus 210 in which the raising can be triggered 3 manually or remotely. The apparatus 210 comprises a 4 number of tiltable wall units 212 which are each attached to a support structure 214 by a hinge 6 bearing assembly 216. The tiltable wall unit 212 is 7 shown in the lowered position in Fig. 6, with the 8 raised Position of the wall unit 212 indicated by 9 the reference numeral 212''. Where elements of the apparatus are similar to the embodiment illustrated 11 in Figs. 1 to 4 these are indicated with the same 12 reference numeral and are not described further.

14 The wall unit 212 may be fabricated from mild steel, aluminium, composite, plastic, lightweight concrete 16 or other suitable material. The support structure 17 214 includes a hinged retaining leaf 80. When the 18 unit 212 is in the lowered position the retaining 19 leaf 80 is also in the lowered position and supports the water retaining lever arm 20. An inflatable 21 rubber membrane 82, which can be inflated like a 22 balloon with pressurised air or pumped water, is 23 provided between the support surface 84 of the 24 support structure 214 and the underside of the retaining leaf 80. Under normal operation, when the 26 unit 212 is in the lowered position, the membrane 82 27 is deflated. However when it is required to raise 28 the flood defence the membrane 82 is inflated by 29 controlling a pump or valve (not shown) . This pushes the retaining leaf 80 upwards to a raised 31 position 80', which in turn pushes the water 32 retaining lever arm 20 upwards, until a point is 1 reached when the whole wall unit 212 automatically 2 tips up to the raised position and remains in that 3 position until such time as the water level has 4 subsided.

6 Figs. 7 and 8 show a flood defence apparatus which 7 can be used to provide additional raising of the 8 level of protection provided by a fixed flood 9 defence wall by up to around 0.6rii.

11 The flood defence apparatus 310 comprises a number 12 of tiltable wall units 312 which are each attached 13 to a support structure in the form of a flood wall 14 314 by a hinge bearing assembly 316. The tiltable wall unit 312 is shown in the lowered position in 16 Fig. 7, with the raised position of the wall unit 17 312 indicated by the reference numerals 312' 19 The wall unit 312 is typically of the order of lm wide and includes a buoyant water retaining lever 21 arm 320 which in the lowered position forms a cope 22 at the top of the flood wall 314, typically 500 to 23 600 mm wide although other widths may be envisaged.

24 On the opposite side of the pivot axis 324 is an abutment lever arm 321 with a counterweight 322.

26 When the water level rises towards the top of the 27 cope, the buoyancy of the water retaining lever arm 28 320 causes the wall unit 312 to tip to the raised 29 position 312' . A locking member 390 of any suitable type may be provided to hold the wall units 312 in 31 the raised position once they have reached this 32 position, thus providing an effective increase in 1 height of the flood wall when the wall unit is in 2 the raised position. The flood wall 314 includes an 3 abutment portion 336 which abuts against the 4 abutment lever arm 321 when the unit is in the raised position. Sealing means (not shown) may be 6 provided on the abutment portion, as described above 7 with reference to Figs. 1 to 4. The flood wall 314 8 also includes a seat 339 which supports the wall 9 unit 312 when it is in the lowered position.

11 The wall unit may be manufactured from steel, 12 aluminium, polypropylene, glass reinforced plastic 13 or other suitable material. The counterweight may 14 be of solid metal.

16 As can be seen in the front elevation view of Fig. 17 8, which shows the flood defence apparatus 310 in 18 the lowered position, the apparatus comprises a 19 plurality of tiltable cope wall units 312 hingedly attached to the support structure 314 arranged to 21 form a continuous wall when in the raised position.

22 There are two types of cope wall unit, first 312A 23 and second 312B units. First units 312A and second 24 units 312B are arranged alternately, such that a first unit 312A is adjacent to two second units 26 312B. The first units 312A are provided with 27 increased buoyancy relative to the second units 28 312B, so that as the wall is raised the first units 29 312A are raised first. The second units 312B have cover plates 392 with laterally extending flanges 31 394 against which recessed portions 396 of the first 32 units 312A can seal when the first units 312A are 1 raised. Because of the increased buoyancy of the 2 first units 312A, the first units 312A urge the 3 second units 312B upwards as they are raised, 4 thereby sealing between the flanges 394 and the recessed portions 396. Any suitable sealing means 6 (not shown) can be fixed to the flanges 394 of the 7 second units 312B to provide a substantially 8 watertight seal between the first and second units 9 312A, 312B when the cope wall units are in the raised position.

12 This embodiment offers an opportunity to provide 13 increased flood protection on an existing or new 14 flood wall 314 without detracting visually. A fixed flood defence wall may be of limited height so that 16 the fixed wall does not disrupt views of the river; 17 typically a fixed wall is not higher than about 1.2m 18 above the landward ground level adjacent to the 19 wall. In the normal lowered position the wall units 312 appear as a cope sitting on top of the wall 314.

21 The wall units 312 may be provided with surface 22 treatment such that the cope blends with the wall 23 and appears as an integrated part of the fixed 24 structure. The effective level of the fixed flood wall may then be raised during flood or extreme high 26 water level conditions by up to about 0.6m. This is 27 a significant amount as it would enable allowance 28 for climate change to be incorporated into many 29 flood defence designs without the disadvantage of disruption of visual amenity.

1 The buoyant nature of the water retaining lever arm 2 20, 320 of the wall units of the invention allows 3 automatic operation of the apparatus as the water 4 level rises. To avoid accidental tipping from the lowered position an actuated locking bolt mechanism 6 (not shown) could if required be provided at the 7 landward side of flood defence apparatus. The 8 locking bolt mechanism could be released either by 9 remote signal from a flood warning system or an operations centre or manually. Similarly the 11 optional locking member 390 which holds the wall 12 units in the raised position may be actuated 13 manually or by a remote signal.

Rather than rely on automatic tipping the invention 16 allows positive tipping of the wall units by any 17 suitable actuating means in all embodiments.

18 Actuating means envisaged by the invention is not 19 limited to the ram assembly 41 shown in Fig. 1 or the inflatable membrane 82 shown in Fig. 6. Any 21 other suitable actuation means may be used, for 22 example an actuating arm operated hydraulically or 23 by a gearing mechanism. The actuation means can be 24 operated remotely by a flood warning signal, or from an operations centre, or locally as a manual over- 26 ride. This arrangement would have the advantage of 27 slower controlled closure during the later stages of 28 tipping and positive closure of the sealing 29 arrangement when the water head against the water retaining lever arm is low. An early warning signal 31 can be provided to warn pedestrians and other 1 persons on the walkway before the locking mechanism 2 (if used) is released and the wall units raised.

4 The invention is not limited to particular materials or dimensions Any suitable hinge mechanism may be 6 used to hingedly attach the tiltable wall units to 7 the support structure.

Claims

1 CLAIMS 3 1. Flood defence apparatus comprising a support 4 structure and

at least one tiltable wall unit hingedly attached about a pivot axis to the support 6 structure, wherein each wall unit comprises a water 7 retaining lever arm and an abutment lever arm 8 arranged on opposite sides of the pivot axis, and 9 wherein the support structure is provided with abutment means adapted to abut against the abutment 11 lever arm to hold the wall unit in a raised position 12 in which the water retaining lever arm extends 13 substantially upwards when the water retaining wall 14 is subject to hydrostatic pressure on its water facing side.

17 2. Flood defence apparatus according to claim 1, 18 wherein the support structure comprises a retaining 19 wall or flood wall.

21 3. Flood defence apparatus according to claim 1 or 22 2, wherein the pivot axis extends close to the 23 centre of gravity of the wall unit.

4. Flood defence apparatus according to any 26 preceding claim, wherein the wall unit includes a 27 counterweight arranged on the abutment lever arm, 28 the counterweight and pivot axis being arranged such 29 that under the action of gravity alone the wall unit is urged towards a lowered position.

1 5. Flood defence apparatus according to any 2 preceding claim, wherein the abutment means 3 comprises a structural element of the support 4 structure provided below the hinge.

6 6. Flood defence apparatus according claim 5, 7 wherein the abutment means includes an abutment 8 surface adapted to engage sealingly with a 9 corresponding abutment surface on the abutment lever arm.

12 7. Flood defence apparatus according to any 13 preceding claim, wherein the wall unit includes one 14 or more buoyant portions in or adjacent to the water retaining lever arm and arranged such that rising 16 water urges the wall unit to the raised position.

18 8. Flood defence apparatus according to any 19 preceding claim, wherein the apparatus comprises a plurality of tiltable wall units hingedly attached 21 to the support structure arranged to form a 22 continuous wall when in the raised position.

24 9. Flood defence apparatus according to claim 8, wherein the wall units comprise first units and 26 second units arranged alternately, such that a first 27 unit is adjacent to two second units, and wherein 28 the first units are adapted to be raised first and 29 are provided with laterally extending flanges against which the second units can seal, while the 31 second units are adapted to be raised after the 32 first units have been raised.

2 10. Flood defence apparatus according to claim 9, 3 wherein the lateral edges of the second units are 4 provided with sealing means adapted to sealingly engage with corresponding sealing means provided on 6 the laterally extending flanges of the first units.

8 11. Flood defence apparatus according to any 9 preceding claim, wherein the lateral edges of the water retaining lever arms are provided with slots 11 adapted to accommodate a stop log.

13 12. Flood defence apparatus according to any 14 preceding claim, wherein the water retaining lever arm is provided with a traffic bearing surface on 16 its side Opposite to its water facing side.

18 13. Flood defence apparatus according to claim 12, 19 wherein the outer edge of the water retaining lever arm is provided with a barrier means adjacent to the 21 traffic bearing surface.

23 14. Flood defence apparatus according to any 24 preceding claim, wherein the support structure includes a recess adapted to house the abutment 26 lever arm and/or counterweight in both the raised 27 and lowered positions.

29 15. Flood defence apparatus according to claim 14, wherein the support structure includes a curtain 31 wall adapted to prevent access to the underside of 1 the wall unit while the wall unit is in the lowered 2 position.

4 16. Flood defence apparatus according to claim 15, wherein the curtain wall includes a cover portion 6 adapted to prevent access to the recess and/or to 7 cover the abutment lever arm while the wall unit is 8 in the lowered position.

17. Flood defence apparatus according to any 11 preceding claim, wherein the apparatus includes 12 actuation means operable to raise the wall unit from 13 the lowered position towards the raised position.

18. Flood defence apparatus according to any 16 preceding claim, wherein the apparatus includes 17 releasable locking means to hold the wall unit in 18 the lowered position.

19. Flood defence apparatus according to any 21 preceding claim, wherein the apparatus includes 22 releasable locking means to hold the wall unit in 23 the raised position.

20. Flood defence apparatus according to any of 26 claims 1 to 10, wherein the water retaining lever 27 arm is in the form of a cope and the support 28 structure is a flood wall, the cope being adapted to 29 provide an effective increase in height of the flood wall when the wall unit is in the raised position.

1 21. Flood defence apparatus according to claim 20, 2 wherein the abutment means is provided at the rear 3 of the flood wall.

22. Flood defence apparatus according to claim 21, 6 wherein the front of the flood wall is provided with 7 a seating means adapted to support the wall unit 8 when it is in the lowered position.

23. Flood defence apparatus according to any of 11 claims 20 to 22, wherein the wall unit is of a 12 material selected from steel, aluminium, 13 polypropylene and glass reinforced plastic.

24. Flood defence apparatus as hereinbefore 16 described with reference to the accompanying 17 drawings.