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A concrete groyne in Ukraine along the coast with the Black Sea.

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Gabions

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Breakwaters are offshore concrete walls that break incoming waves out at sea so that their erosive power is reduced when they reach the coast. Breakwaters are effective but they can be easily destroyed during a storm and they can be an eyesore.

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Here is an example of a revetment. Costs = Moderate (£2000 to £50,000/100m frontage length).

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Disadvantages -- Aesthetics

Gabion structures have suffered a reputation for being unsightly and unnatural in river, pond and beach settings. The front-facing walls appear bland and mechanical in design, rather than form natural-looking rock barriers. Large gabion walls constructed on tourist beaches serve as a distraction, where very thick and long walls must be used to protect large beach areas.

Disadvantages -- Maintenance

If the rocks shift or become worn down inside the metal baskets as a result of heavy water and wave activity, the entire wall must be disassembled to reached the damaged area. For very tall gabion stacks, any damage to the lower areas requires the removal of the upper wall elevations, which can be costly and time-consuming.

Disadvantages -- Wall Assembly and Cost

Although gabion walls offer a good economic choice for most applications, they remain more expensive to install than natural vegetated slopes or riprap. Gabion walls require heavy equipment to construct, since mechanical lifting is required to set heavy walls sections in place.

Disadvantages -- Endurance

In instances of high velocity streams and wave interaction, gabion wall wire mesh baskets can abrade and tear open, spilling the rock fill.

Disadvantages -- Inspection

Gabion walls must be inspected on a regular basis to insure their integrity. They must also be immediately inspected and evaluated after any storm, which has caused heavier than normal water flow.

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A sea wall is a wall or embankment to protect the sea eroding and destroying the land and to protect settlements. They are often recurved which means waves are reflected back on themselves.  This can cause the erosion of material at the base of the sea wall.

Cost: £3000-4000/m

Limitations + Potential Problems:
-Expensive to build.
-Curved sea walls reflect the energy of the waves back to the sea. This means that the waves remain powerful. Over time the wall may begin to erode.
-The cost of maintenance is high.

This is a photo of a sea wall

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Revetments are concrete or wooden structuress built along the base of a cliff. They’re slanted and act as a barrier against waves. They absorb the wave's energy, preventing erosion of the cliff. They can be modified so that they have rippled surfaces, which helps to dissipate the wave energy. Revetments are usually successful at reducing coastal erosion but are expensive to build. Once built however, they don’t require as much maintenance as a sea wall

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Gabion Benefits of Gabions

Flexibility: Subjected to alternating forces of tension and compression, the inherent flexibility of a Gabion structure enables it to deform rather than break. This prevents loss of structural efficiency. Deforming in response to subsidence of foundation or internal stress is a functional feature, and rather than being a fault is in fact, a benefit.

Strength: Since Gabion are bound together as a monolithic unit, the wire mesh is extremely strong under tension. The wire mesh shell is not simply a container for the stone filling, but a reinforcement of the entire structure. Additional strength is achieved by the use of vertical diaphragms. These diaphragms are affixed to the base of the gabions to restrict internal movement of the stone filling and provide further reinforcement. Gabion efficiency, rather than decreasing with age, actually increases. During early periods of use, silt and vegetation will collect within the rock filling to form a naturally permanent structure, enhancing the environment.

Permeability: Interstitial spaces in the stone fill within the baskets provide a great degree of permeability throughout the structure eliminating the need for a drainage system and preventing buildup of hydrostatic pressure which will displace and crack concrete structures. In river works, pressure and counterpressure on the banks due to variations in water depth between flood and low water are therefore also eliminated.

Economy: Wire mesh gabions are less expensive than most construction materials. Graded stone fill is usually locally available. Waste materials such as crushed concrete may be specified in place of stone.

Construction costs are reduced; unskilled laborers can easily learn to erect Modular Gabion Systems, fill them and close them properly. Many gabion structures may be built without any mechanical equipment. Pilings, underwater drainage systems and excavations are unnecessary. There's no need to drain the site or to construct a cofferdam for underwater installation. The first layer of gabions can be laid in water or in mud.

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Picture of a sea wall 🌊💦

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One way to protect beaches from being swept away is to build barriers, called groynes. These trap sand which the waves have moved along the beach and prevent the sand being moved too far along the coast. A man-made barrier built across a beach (from the back of the beach down into the sea). Groynes are usually made of wood or concrete and are built to trap sand and hold it on the beach. The average groyne costs £150,000 to construct and install.

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Rock or other materials used to protect coastlines from wave erosion. Also known as Riprap

How does it operate?

Works by absorbing and deflecting the impact of waves before they reach the defended structure

Cost?

£13.37 for an 8 tonne load

Limitations?

- Visual pollution
- Requires maintenance

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As the variety and scale of demand made on coastlines has grown so the need for management has increased. Hard engineering involves the construction of structures, to control or prevent natural processes that threaten property, harbours and tourist amenities.
Breakwaters are offshore structures of concrete or boulders, they deflect or absorb wave energy before it reaches the shore. If poorly aligned they can deflect waves to erode at other points on the shore.
Revetments are sloping ramps build with open baffles of concrete, wood or rocks. They are designed to absorb wave energy. They are visually intrusive they can be undermined and can damage beach and shore ecosystems. Below is an example of a breakwater

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Groynes are constructions built perpendicular to the shoreline to limit longshore drift, increase sedimentation rates and build up beaches.

Advantages;

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Sea Walls
Rock Armouring
Gabions
Groynes
Revetments
Breakwaters

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What are some reasons why our coastlines need protecting?

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What are some reasons why our coastlines need protecting?