Manage the Coast

You cannot defend all of it

You already know how waves erode a headland into a cave, an arch and finally a stack. Coastal management starts from the fact that this is going to keep happening. So the real question is never "how do we stop the sea?" It is which stretches are worth defending, with what, and what happens to the coast next door once we do. Every answer in this topic is a cost-benefit argument.

What the sea takes

Two processes threaten people on the coast, and they are not the same thing:

The defence that causes erosion

A seaside town builds a long line of groynes. A few years later, the next stretch of coast down the shore is eroding faster than before. Why?

• The groynes trap sediment moving by longshore drift, so the coast beyond them is starved of the beach that protected it
• The groynes make the waves bigger further along the coast
• It is a coincidence, since defences only affect the beach they are built on
• Sea level rose specifically at that point on the coast

Two philosophies

Management approaches split into hard engineering, which builds something to resist the sea, and soft engineering, which works with natural processes instead.

Match each defence to how it actually works

The price of concrete

Select the TWO genuine drawbacks of hard engineering.

• It has a very high build cost, and a sea wall is the most expensive option per metre
• It can increase erosion elsewhere on the coast
• It has to be replaced every single year
• It is not permitted anywhere in the UK

Letting it go, on purpose

Managed retreat, also called coastal realignment, means deliberately allowing low-value land to flood or erode instead of defending it. It sounds like giving up, and examiners reward students who explain why it is not. The flooded land becomes salt marsh, which absorbs wave energy and protects what lies behind it, permanently and for almost nothing. The honest costs are real too: landowners lose farmland, and someone has to compensate them.

The rational case

Under what circumstances is managed retreat the rational choice for a stretch of coast?

• When the cost of defending the stretch is greater than the value of what is behind it
• Whenever a council has run out of money for defences
• Never, because losing land is always the worst outcome
• In town centres, where the most people would benefit from new salt marsh

The Jurassic Coast, Dorset

This is the named coastline to write about, and it makes an unusually sharp argument. The Jurassic Coast is a World Heritage Site, designated for the rock exposures that record millions of years of Earth history. Those exposures survive only because the sea keeps eroding the cliffs.

You are the coastal officer

You advise a Dorset council with a limited budget on three stretches of the same coastline. Take them one at a time.

• Stretch one is the town seafront: hotels, homes and the businesses the town lives on. What do you recommend?
• Stretch two is low-lying grazing farmland behind a crumbling earth bank. Defending it would cost more than the land is worth. What do you recommend?
• Stretch three is undeveloped World Heritage cliffs. A councillor asks why you are not protecting them too. What is your answer?

Plan the answer

A management question is really a decision process. Put its stages into the order that produces a full-mark answer.

• Identify what is actually at risk on this specific stretch
• Judge the value of it: homes and businesses, or farmland and open cliff
• Set out the realistic options, hard and soft, with their costs
• Work out the knock-on effects further along the coast
• Decide, justify the decision against the alternative, and say how it will be monitored

Hard and soft defences

Cliffs retreating and taking land with them is coastal _____. A concrete barrier that reflects wave energy is a _____, and timber fences that trap sediment moving along the shore are _____. Deliberately allowing low-value land to flood is called _____, and the habitat it creates, which absorbs wave energy, is _____.

Evaluate the strategy

"Hard engineering is the best way to manage a coastline." Using the Jurassic Coast in Dorset, evaluate this statement and reach a conclusion.

• Give one stretch where hard engineering IS the right answer, and say why in cost-benefit terms
• Give one stretch where it is not, and explain what is done instead and why
• Explain one knock-on effect that hard engineering can have further along the coast
• Refer to the named coastline throughout, not to coasts in general
• Finish with a conclusion that answers "best" rather than listing both sides