GB2459638A - Coastal defence system - Google Patents

Abstract

A wave energy dissipation device comprises a base member having, at its seaward edge, a primary wave impact member and, at its landward edge, a land armour protection member which presents an angled surface to the advancing waves. The device has a gap or cavity between the primary wave impact member and the land armour protection member, to further enhance the dissipation of wave energy. When deployed at ground level the invention reduces wave impact force to a fraction of its original strength which has the effect of slowing coastal land erosion. In time residual erosion is focused into a specific area of elevated land just above the land armour protection member so that a platform area is created for a second layer of devices to become joined to the first. Once the structure gains sufficient height its function alters from reducing erosion to that of a robust coastal defence barrier which is ultimately intended to prevent coastal flooding. The periodic upgrading of the structure as and when required is intended to significantly ease the financial burden of providing coastal barriers at a time when climate change has started to melt quantities of ice that are already causing measurable increases in global sea levels.

Description

Small coastal defence system This invention introduces a new class of small and affordable coastal defence system which allows protection against coastal erosion to become more accessible to consumers wishing to defend their land and property. It is referred to as a coastal defence system because horizontal deployments reduce erosion while vertical upgrades over time (as and when required) prevent coastal flooding.

Introduction

In order to reduce coastal erosion it is necessary to halt or significantly reduce wave energy impacting against coastal land. While it is possible to defeat waves with large bulky structures the challenge is to intercept wave energy in an efficient and cost-effective manner which, ideally, also makes provision for people to enjoy existing beach areas for recreational purposes.

One of the biggest problems that discourages protection of land from the sea is the huge cost of traditional coastal defence schemes that primarily focus on absolute coastal protection for essential public infra-structure. These coastal protection schemes cost millions and usually have to be financed by central government after very detailed and lengthy considerations.

The initial purpose of the invention (in its cheapest configuration) is to provide substantial but not total protection from coastal erosion, in practical terms this means that coastal property owners can deploy the invention and effectively delay erosion in a chosen location. Once the invention is deployed it can be upgraded horizontally or vertically allowing customers the flexibility to protect coastal land either partially or totally depending on the urgency of the situation.

The invention will now be described making references to the following drawings.

Figure 1 demonstrates coastal erosion in a before and after scenario based on photographs of coastal landslides located in East Anglia (UK).

Figure 2 shows the side profile of the structure with descriptions.

Figure 3 shows thc invention deployed on a iypicai beach iocation with the sea at low tide in conjunction with traditional (East Anglian) coastal defences. (This diagram seeks to highlight the recreational opportunities and advantages that this invention offers.) Figure 4 shows the invention (at high tide) in conjunction with a typical one metre wave (drawn approximately to scale in relation to the primary impact zone which is also one metre high) about to impact the invention. Waves of this size are considered to be absorbed with little or no contribution to land erosion.

Figure 5 shows the invention deployed with the sea at high tide in conjunction with a two metre wave about to impact the coastal defence structure. This image contains a simultaneous estimation of impact splash, filled cavity area and residual seawater momentum exiting the structure.

Figure 6 is an impression of the likely (elevated) land reshaping that will probably occur based on erosion patterns associated with soft coastal land located in East Anglia (U.K).

Figure 7 shows a variant of the basic design that is intended to be used in an elevated position and designed to reinforce existing (lower level) land armour that will become subject to greater impact forces as sea levels rise.

Figure 8 shows an impression of the invention in its coastal defence barrier configuration.

Figure 9 shows a variant of the basic design that is intended to protect property that is uncomfortably close to falling into the sea.

To gain some idea of scale, the primary impact zone (in figure 2) is one metre tall while the overall length of the structure is a proportion (approximately I.5x) of the gap between the leading edge of waves in a particular deployment location.

In order to appreciate some of the drawings and invention features it is necessary to review an aspect of coastal erosion land mechanics. When soft elevated coastal land is undermined by erosion, wave impacts can start a landslide which frequently results in slopes that have an angle of approximately 45 degrees. In areas with coastal land that has a similar strength to chalk huge quantities of unprotected coastal land can relocate with the ferocity and speed of avalanches.

(Figure 1) When the invention is compared to the original lines of "wooden post" coastal defences that were deployed around the 1 950's in the East Anglian (U.K) region (figure 3) it is fairly obvious that recreational users of the beach cannot gain access to the water and views of the sea are diminished.

Unlike traditional coastal defences located on beaches the invention is deployed against land to be protected (to the rear of beaches) which means that the structure will not excessively interfere with tourists or users.

How the invention works Traditional coastal defence structures work by resisting the impact force of waves, this invention works on the principle of wave attrition using a variety of sequential methods that avoid having to engage the full force of a wave strike. Once wave energy is reduced residual seawater momentum strikes land armour which provides a final defence against erosion.

The invention (see figure 2) initia!ly interacts with waves by partially impacting and climinating movement of seawater up to a specified height (figure 4). Waves that have sufficient height to pass over the primary impact zone (figure 5) are briefly supported by the structure but then fall and disperse into a cavity capable of significant and rapid drainage. The goal of the cavity area is to be in the act of draining at the time the next wave falls in as there is a beneficial dispersion force if incoming water strikes departing water. Residual wave content which maintains enough forward momentum is directed towards sloped land armour which converts remaining kinetic energy to potential in a relatively gentle action. Seawater that manages to travel completely up the slope will impact elevated land with significantly reduced energy when compared to a unmitigated wave strike.

The variant shown in figure 9 has a custom made length of land armour that reaches beyond the effective height of waves (at the time of deployment survey) in order to maximise protection against erosion. This variant is not as cost effective as a standard structure but is intended to provide a unique service to properties that are uncomfortably close to destruction.

Sea levels are rising as global warming melts ice. The extra global height of seawater is already reshaping the map of the world as low lying islands effectively sink, over the next century the effects will become considerable. The invention is intended to make coastal defences more attractive to investors by offering an immediate mechanism to combat coastal erosion while providing the foundations for a substantial coastal barrier that can be more fully constructed over a period of decades as and when needed allowing capital sums of investment money to be significantly reduced.

Figure 6 shows time delayed and reduced quantities of erosion eventually forming a useful platform shape on to which another layer of the invention adds to the overall height of the coastal defence structure.

Figure 7 highlights a elevated variant of the invention which replaces ground level foundations with a structural support system that facilitates the inventions secondary usage as a coastal barrier.

Figure 8 shows multiple tiers of the invention that compact the protected land mass, the front former foundation shape has a new purpose of binding together and reinforcing the forward facing structure in a similar fashion to grass binding the soil used in Dutch sea dykes. As sea levels rise the initial land armour segments benefit from extra structural support as wave strikes gradually move higher.

The invention is constructed from (marine grade) steel reinforced concrete and forms a passive structure that has only to be deployed and joined together before it begins to function.

Advantages The invention represents the first use of sequential wave attrition methods (impact, dispersion and kinetic to potential energy transfer) to mitigate wave strength in a small integrated structure whose length is related to the gap between waves in a specific location.

The use of land armour as part of a coastal defence system upgrades the strength of soft land mass such as chalk towards the strength of granite.

The combination of wave attrition and land armour represents one of the most effective methods to combat coastal land erosion.

The invention is designed to work towards the top end of its performance specification on a daily basis (at high tide levels) rather than traditional larger, substantially more expensive coastal defence structures which are primarily designed to resist periodic storm force waves.

The relatively small volume of the invention related to the quantity of erosion that it prevents means that this invention is deemed to be efficient and cost-effective when compared to larger structures.

The dual purpose of this invention means that when climate change and rising sea levels cause coastal flooding and the phenomenon progresses from affecting a small number of people to a significant quantity of the population, existing installations will already be in place at ground level for almost immediate upgrade into small coastal defence barriers.

Global warming will cause sea levels to rise over a period of decades. The gradual union of multiple segments solves the biggest coastal defence problem of capital project finance by effectively turning a erosion device into a capital barrier for the price of a few upgrades as and when required.

Managed coastal erosion that occurs above the height of the land armour segment will cause the remaining land to be shaped in a predetermined fashion that partially prepares the installation site for additional segments to be deployed with reduced digging costs and landslide risks. (Figure 6A-C) A supplementary use of the invention allows recreational beach users who may be inconvenienced or even trapped by rising tides to gain additional time to vacate beaches more safely by using the cavity area behind the raised impact zone as a sheltered pathway from encroaching waves.

The invention represents the first use of "organic planning" in construction where natural processes such a waves reshaping land determine the optimal scheduling of additional building work.