GB2491011A - A Self-raising Flood Protection Barrier - Google Patents

Abstract

The invention relates to a flood barrier B connected by a hinge H along a lower edge to a base, such that the barrier may rotate about the hinges axis. The barrier is made to float when only partially immersed in water, such that the barrier rises from a prone at rest position, to an upright in use position as the flood water level rises. A float chamber may be incorporated into the barrier to achieve the desired buoyancy. When the barrier is rotated to an in use upright position, the base is preferably brought into firm contact with the base such that a compression seal C is formed between the barrier and the base.

Description

A Self-raising Flood Protection Bather

Description

The barrier for protection against flooding here described is so designed and constructed that, when once installed, should the surface of water to one side of it rise to a level that would otherwise inundate an area on its other side which it is intended should be kept free of inundation, the bather is raised by the pressure of the rising water against its wetted face to a more upright position that prevents flooding from oecurring.

The barrier (B, Figsla,b,c) has a foundation appropriate to the ground conditions upon which it is to be erected, adequate to support the maximum thrust exerted upon it and the overturning moment transferred to it by the barrier when raised to withstand a flood at the maximum height for which it is designed. The bather is hinged (H, Figs la,b,c) to its foundation along the leading edge of its base, that is, along the bottom edge of its face in contact with the water when raised in use.

When not in use, the bather rests in a prone position upon the ground, or other exposed surface between its foundation and the water's edge, while water levels are normal and safe (Fig.la). The bather has a relatively light structural section so that it is sufficiently buoyant to float in water when only partially immersed. Should the water level rise to a height such that flooding of the area to be protected could occur, floatation of the bather is initially achieved (Fig. la). Thereafter, as the water level may rise further, the barrier is rotated to an increasingly upright position by the pressure of the water against its wetted face (Fig. lb), until finally its base may be brought into finn contact with the foundation, forming a secure compression seal (C, Fig. lc), and the barrier is in its fully raised position.

A bather inclined towards the flood it is resisting when in the fully raised position has the advantage that its centre of gravity may be located towards the flood water relative to the hinge, H, so that as the flood subsides the barrier returns to the initial prone position. Should the centre of gravity of the design section be to the landward' side of the hinge, some device such as a trough along the flood' face, filling with water as the flood rises, may be added, to provide the moment needed to induce lowering as the flood recedes (Fig. Id).

Should the chosen design section not quite achieve floatation, or at a sufficiently early stage, a suitable float chamber may be incorporated into the design to achieve the desired buoyancy (Fig. 1 e).

In certain circumstances an inclined contact' face for the foundation may be preferred (Fig. 10.

Should the body, or stream of water be abutted by a wall too low to contain more severe floods, the bather may be mounted so as to hang below the top level of the wall, provided that its centre of buoyancy (C.B.) is towards the body or stream relative to the hinge (Fig.lg).

Should space to accommodate a bather above such a wall not be available, it may be mounted on a cantilevered ledge to provide a base of sufficient width to support it in the raised position (Fig. lg).

In some circumstances, a flood side' vertical face, or one inclined away from the flood, may be preferred. In such instances, returning the barrier to its not in use' prone position would require manual or mechanical intervention (Fig.lh).

The bather may be of any structural material possessing the necessary strength in compression, shear and flexure at safe working stresses, resistance to fatigue, and to corrosion, whether inherently, by surface treatment, or application of a surface coating, having due regard to durability, environmental, aesthetic and other economic considerations.

The structural section may be any having a section modulus such that all stresses within the material shall comply with applicable safe limits, having regard to economic factors of quantities of material, simplicity, speed and ease of manufacture, fabrication, assembly and installation, as also any environmental, or aesthetic restraints that might be imposed.

The requirement that the barrier should float is favourable to the use of structural materials of lighter weight and thinner section to achieve a design section of adequate section modulus. A wide variety of suitable sections are possible, only several of which are illustrated in Figure 2. Figures 2a, 2b and 2c show three alternative tapered stiffened box sections, while Figures 2d and 2e show two alternative tapered corrugated sections with a continuous stiffening backing plate along their rear, landward' faces. Corrugated sections even without a backing plate are feasible, provided that their upper and lower ends, the crest and base of the bather, respectively, are sealed by a continuous sheet, or plate, to prevent ingress of flood water to the inner, landward' corrugations, and to provide a satisfactory compression seal between base and foundation.

The practicality of continuous rising flood barriers of more than a restricted length requires that in the majority of situations such barriers would need to be constructed in modules, or units of convenient length, overall dimensions and weight. This limitation requires a gap between adjacent units to provide a sufficient construction tolerance, and an effective watertight seal to be incorporated into the barrier's overall design along the full height of their adjacent rear -or leading -edges. One suitable such seal is shown in Fig.2f, a bracket along the full height of both edges of alternate units to which is bonded a compressible sealing strip (C). As the bather rises with the rising flood water, the edges of intermediate units will be pressed against these strips, so as to provide an effective seal while the bather remains in the fully raised position, as shown in Fig.2g, the part section indicated in Fig.2f to an enlarged scale.

This arrangement facilitates dismantling and removing units for maintenance, or repair, and for reinstalling or replacement, the units with seals accessed directly, intermediate units by first raising the seal' units either side in order to gain access. While the barrier may likewise be dismantled for storage off site, this would require space for such purpose, transport from and to site, with the risk, due to a sudden flash flood, of not having the barrier in place in time to prevent flooding, and is here not recommended.

Instances may arise where a change of direction, or alignment, is required, as at intervals along the inner, convex, bank of a river, or along the outer, concave, one. The former situation gives rise to a reflex angle between adjacent units (Fig.2h), the latter an obtuse one (Fig.2i). The former does not present a serious problem, as the adjacent ends of the two units immediately either side of the change may readily be shaped to accommodate this, with a constant minimum construction tolerance gay, as viewed from above in Fig.2h, the units raised shown in full lines, and in the prone position, dashed.

The reflex angle situation is more complex. If the change in alignment is relatively small, the adjacent ends of the two units immediately either side of the change can be shaped to provide a constant minimum construction gap in the prone position, but with the bracket (Fig.2f) for the compression seal shaped as a trapezium, its upper edge extended to span the linearly increased gap between the two adjacent units in the fully raised position, set at the angle of alignment change to accord with the edge of the adjoining unit with which the seal is to make contact. An alternative practical solution, which may prove acceptable, is to construct a narrow, tapered, columnar section of barrier in the permanently fully raised position across the point of alignment directional change as suggested in Fig.2i. The seals (Fig.2f) would require to be mounted along both edges of such a fixed columnar section.

The barrier described in the foregoing pages has the potential to be installed also at coastal locations to protect against severe storms and tidal surges (Figure 3), possibly even tsunamis.

At such locations, where severe storms or exceptional tidal surges are likely to occur at only infrequent intervals, they could prove visually less intrusive and inconvenient during the extended periods for which protection is not necessary than fixed walls of the height and size that would otherwise be required. Both the structural sections of the barriers and the foundations to support them adequately would generally need to be more substantial than for inland situations. Close attention would need to be paid to the structural implications of repeated dynamic impact by storm waves (Fig.3a), and alternatives carefUlly examined for each individual situation to achieve a practical solution.

In the case of tidal surges, such as those induced by tsunamis, the momentum of the disturbed mass of water is probably the most serious challenge. Shaping the seaward faces of both foundation and barrier so as to divert the flow upwards, thereby creating a horizontal vortex in front of the barrier, and directing the bulk of the flow skywards, for gravity to reduce its kinetic energy, thus dissipating the force it would otherwise exert directly against the barrier, is one possible method of achieving a viable solution (Fig.3b). Claim