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Unlock This CourseWaves erode cliffs and storm surges flood low land, so people try to protect homes, roads and farmland. Remember that hard engineering means building artificial structures and soft engineering means working with natural processes. Coasts use both. You need to evaluate them: for each one, say how it works, its advantages and disadvantages, its cost, and what it does to the coast further along.
That last point matters because of longshore drift, which carries sand and shingle along the coast. If a structure stops the material, places further along lose their supply.
| Technique | How it works | Advantages | Disadvantages | Cost and effects along the coast |
|---|---|---|---|---|
| Sea wall | A strong concrete wall at the foot of the cliff or the edge of the town. It stops waves reaching the land. | Very effective. Lasts many years. Gives a promenade for walking. | Ugly. Waves bounce back and scour (dig out) the beach in front, so the wall can be undermined (weakened from below). | Very high cost, plus repairs. Erosion can increase at the unprotected ends. |
| Recurved sea wall | A sea wall with a curved top that throws the wave energy back out to sea. | Better at stopping waves going over the top. | Even more costly to build. Still sends reflected wave energy on to the beach. | Highest cost of the walls. Same problem of passing erosion on. |
| Groynes | Wooden or rock fences built out into the sea at right angles to the beach. They trap sand moved by longshore drift. | Cheap. Builds a wider beach, which absorbs waves and helps tourism. | Not very attractive. The beach is only wider on one side of each groyne. | Low to medium cost. Starves beaches further along the coast of sand (cuts off their supply), so erosion increases there. |
| Rock armour (rip rap) | Big boulders piled at the foot of the cliff or in front of a wall. They break up the waves. | Fairly cheap and easy to build. Needs little maintenance. | Rocks are often brought from far away. Can look ugly and make it hard to reach the beach. | Medium cost. Can pass erosion on to the next stretch of coast. |
| Gabions | Wire cages filled with rocks, stacked against a cliff or bank. | Cheap and quick to build. Water drains through them. | The cages rust and break, so they do not last long. Weak against big waves. | Low cost, but they need replacing. Only suit places with low wave energy. |
| Revetments | Sloping slatted wooden or concrete barriers in front of the cliff. Waves pass through the gaps and lose energy. | Cheaper than a sea wall. Absorbs wave energy. | Needs repairing often. Can look ugly. | Medium cost. Protects only the part of the coast where it is built. |
| Offshore breakwaters | Rocks or concrete blocks placed in the sea, parallel to the shore. They make waves break before they reach the coast. | Reduces wave energy for the whole beach behind it, and sand builds up there. | Expensive. Dangerous for boats and swimmers. Can look ugly. | High cost. Can change the pattern of drift and starve beaches further along. |
After a hurricane storm surge killed thousands of people in 1900, the city of Galveston in the USA built a large concrete sea wall. It still protects the city, and shows how a big, costly hard structure can save lives where many people live.
Sand is brought from elsewhere and added to the beach. A bigger beach absorbs more wave energy. It looks natural and helps tourism, but the sand is washed away, so it has to be repeated. It is costly, because sand must be bought, moved and replaced again and again. Miami Beach in Florida is nourished this way.
Bulldozers push sand from the lower beach up to the top, making the beach steeper and higher. It is cheap and uses the beach's own sand, but it must be repeated after storms.
Marram grass is planted and fences are built to trap sand, so dunes grow. Dunes act as a natural barrier to the sea. It is cheap and good for wildlife, but people walking over the dunes can damage them.
Defences are taken down and the sea is allowed to flood low land, which can turn into a salt marsh that soaks up wave energy. It is also called managed realignment. It is cheap to carry out and creates a habitat, but farmers and homeowners lose land.
The slope of a cliff is made gentler, so it is less likely to slump (slide down). It reduces the danger of collapse, but it is expensive and needs a lot of land.
Pipes and drains take water out of a cliff, so it is lighter and slides less. It is fairly cheap, but it does not stop the waves at the base.
Soft engineering is usually cheaper and looks more natural than hard engineering. It does not cut off the sand supply, so it does less harm further along the coast. Sand added to one beach may even drift along and help the next. Its weakness is that it protects less strongly in a big storm.
Key terms:
Hold the line is used for towns and ports, where the land is worth a lot. No active intervention is used where the land is worth little and the defences would cost more than the damage. Advance the line is very costly and rarely used, but it can create new land for building or ports. At Medmerry in West Sussex, England, new banks were built inland and the old shingle bank was breached in 2013, so the sea could flood farmland and form a wetland that protects villages behind it.
Sustainable coastal management meets today's needs without harming the future. For the coast, it means working with natural processes, being affordable over the long term, and not harming people or wildlife further along the coast. Ask these questions:
Hard engineering protects best where many people and buildings are at risk, but it is costly and can move the problem on. Soft engineering is cheaper and more sustainable, but gives less protection. Most places use a mixture, chosen by the value of what is being protected.
Fig. 1.1 describes Carrow, a made-up coastal town. It has 4,000 people, a promenade and a sandy beach that is losing sand. Along the coast, east of the town, is low farmland worth little money. A sea wall is proposed for the town.
(a) Identify two types of hard engineering. [2 marks]
(b) Explain how beach nourishment helps to protect a coast. [3 marks]
(c) Evaluate a plan for Carrow that holds the line for the town and uses managed realignment for the farmland. [6 marks]
(a) Any two from: sea wall (1); groynes (1); rock armour (1); gabions (1); revetments (1); offshore breakwaters (1).
(b) Sand is added to the beach (1). A bigger, higher beach absorbs more wave energy before the waves reach the land (1). A bigger beach also makes waves break earlier, so it protects the cliff and buildings behind it (1).
(c) Level 3 (5-6 marks): a balanced, developed evaluation with a clear judgement. For example: Holding the line with a sea wall protects 4,000 people and the promenade, which brings in tourists, so it is worth the high cost. However, a sea wall can make erosion worse along the coast beyond the end of the wall. Managed realignment on the low farmland costs little and lets the sea flood land of low value, where a salt marsh can form and absorb wave energy, helping to protect the town. Farmers would lose land, though, and may need compensation. Overall the plan is sensible, because it spends money where the value is highest and works with nature on the rest.
Level 2 (3-4 marks): some points on both parts, with some explanation but little judgement.
Level 1 (1-2 marks): simple ideas only, for example: A sea wall stops the sea.
In "evaluate" questions, use cost, effect further along the coast, and who benefits, then end with a clear judgement.