Coastal Management: Hard Engineering

Types of Hard Engineering

Sea Walls

Sea walls are strong concrete or stone barriers built along the coast to reflect wave energy back into the sea. They prevent the sea from eroding the base of cliffs or flooding coastal land. Sea walls often have a curved shape to deflect waves upwards, reducing their impact.

Groynes

Groynes are wooden, stone, or concrete structures built at right angles to the coastline. Their purpose is to trap sediment moved by longshore drift, building up the beach. Longshore drift is the movement of sediment along the coast by wave action. A wider beach acts as a natural barrier, absorbing wave energy and reducing erosion.

Rock Armour

Rock armour, also called riprap, consists of large boulders placed at the base of cliffs or along the shore. These rocks absorb and dissipate wave energy, reducing erosion and protecting the coast behind them.

Gabions

Gabions are wire cages filled with rocks or stones, placed along the coast to absorb wave energy. They are flexible and can be stacked to form walls that protect cliffs and shorelines from erosion.

Purpose of Hard Engineering

• Prevent coastal erosion by absorbing or reflecting wave energy
• Protect homes, businesses, roads, and other infrastructure near the coast
• Reduce the risk of flooding from the sea, especially during storms and high tides

Hard engineering is often used in areas where valuable land or property is at risk and where immediate, strong protection is needed.

Advantages of Hard Engineering

• Effective immediate protection: Structures like sea walls and groynes provide strong barriers against waves and storms, reducing erosion and flooding quickly.
• Long lifespan: Many hard engineering structures last for decades if maintained properly, offering durable coastal defence.
• Supports tourism and recreation: By protecting beaches and coastal towns, hard engineering can help maintain areas popular for holidays, fishing, and water sports.

For example, groynes help maintain wide sandy beaches that attract tourists, benefiting local economies.

Disadvantages of Hard Engineering

• Expensive to build and maintain: Construction costs can be very high, and ongoing maintenance is needed to repair damage from storms and wear.
• Environmental damage: Hard structures can harm coastal ecosystems by changing natural habitats and disrupting wildlife.
• Disrupts natural sediment movement: Groynes trap sediment on one side but cause increased erosion further down the coast where sediment supply is reduced.

This can lead to “terminal groyne syndrome,” where beaches beyond the last groyne become narrower and more vulnerable to erosion.

Learning Example: Calculating the Cost of a Sea Wall

Suppose a sea wall costs $\text{£}3,000$ per metre to build. A coastal town needs a 500-metre sea wall to protect its properties.

Total cost = cost per metre $\times$ length

$\text{£}3,000 \times 500 = \text{£}1,500,000$

So, the town must spend $\text{£}1.5$ million to build the sea wall.