B.3 Managing coastal margins

Why coasts need managing

Coastal management is the planning and action people take to reduce erosion and flood risk on a coast and to balance its different uses.

Coasts need managing because natural processes and dense human use meet there. Destructive waves erode cliffs, longshore drift moves sediment along the shore and storms push water inland as a storm surge, while homes, roads, ports and power stations stand at the water’s edge. About 40% of the world’s population lives in coastal zones, which make up less than 15% of the Earth’s land area.

Two different hazards are managed, and one strategy rarely deals with both equally well. Coastal erosion is the permanent loss of land as waves and weathering wear back cliffs and remove beach sediment; it is usually gradual, metres a year on soft rock. Coastal flooding is the temporary covering of low land by the sea, usually during a surge at high tide; it is sudden and can be deadly, as in the North Sea flood of 1953, which killed 307 people in the United Kingdom and over 1,800 in the Netherlands.

Coastal flood risk depends on the hazard, on exposure (the people and assets in its path) and on vulnerability (how easily they are harmed). A sea wall reduces the hazard, moving homes reduces exposure, and warnings and insurance reduce vulnerability. Good management usually combines all three.

A coast is a system

Coastal sediment moves within sediment cells, lengths of coast in which sand and shingle are supplied, moved by longshore drift and deposited, with little exchange with neighbouring cells. Because the system is connected, a structure that traps sediment in one place starves the beaches downdrift of it, so protecting one stretch of coast can increase erosion on the next. For this reason coastal plans in many countries now treat the whole sediment cell, not one town’s seafront, as the unit of management.

Sea-level rise adds pressure everywhere. Global mean sea level rose by about 4.6 mm a year in 2013–2022, roughly twice the twentieth-century average, and where the land is also sinking the relative sea-level change is far faster. Every defence built today must cope with higher water and bigger waves in future, or be replaced.

Hard engineering

Hard engineering uses built structures of concrete, rock, steel or timber to resist the energy of the sea. It is the traditional approach where valuable land lies behind the coast: town centres, ports, railways and power stations. It gives a high and predictable standard of protection, but it is expensive, needs maintenance, changes the look of the coast and often interferes with sediment movement.

Hard structures work in one of three ways: they reflect wave energy back out to sea (vertical walls), absorb it by making waves break over a rough or sloping surface (rock armour, revetments, gabions, breakwaters), or trap sediment so that a wider beach absorbs the waves (groynes).

Sea walls and revetments

A sea wall is a wall of concrete, stone or steel along the back of the beach that stops waves reaching the land. Many have a recurved lip that throws breaking waves back seaward. Reflected waves churn up the beach in front of the wall and carry sand offshore, so the beach level drops and the foot of the wall is exposed. This toe scour can undermine the wall unless it is protected with rock or deep foundations.

A revetment is a sloping structure of concrete, stone, timber or loose rock against the cliff foot or the back of the beach. Waves run up the slope and lose energy instead of slamming against a vertical face, so it causes less scour than a wall. Impermeable revetments are usually designed to last 30–50 years.

Rock armour and gabions

Rock armour (rip-rap) is a pile of large boulders, often hard rock brought from elsewhere, at the foot of a cliff or sea wall. The rough surface and the gaps between rocks break waves and absorb their energy. It is fairly cheap where rock is close by, but it looks out of place, blocks access and can be shifted by storms.

A gabion is a wire-mesh cage filled with stones, stacked as a wall or slope. Gabions are cheap and can use local stone, so they suit places where large rocks are unavailable or long-term protection is not justified, but the wire corrodes in salt water and on exposed coasts they may last only 5–10 years.

Groynes and breakwaters

A groyne is a low wall of timber, rock or concrete built out from the shore at right angles to trap sediment moving by longshore drift. Sand builds up on the updrift side of each groyne, widening the beach, and a wide beach makes waves break and lose energy before they reach the land.

Groynes work by holding back sediment, so downdrift of the last groyne the beach is starved and erosion speeds up: the terminal groyne effect. At Mappleton on the Holderness coast of England, a £2 million scheme in 1991 built two rock groynes and a revetment to protect the village, where the till cliffs had been retreating by about 1.7 m a year between 1952 and 1989. The village was saved, but erosion increased on the cliffs immediately to the south, where the land was mostly farmland. The scheme was a trade-off: it protected one community by moving the cost downdrift to landowners who had no right to compensation, which is why shoreline management plans now judge schemes across a whole sediment cell rather than one frontage at a time.

An offshore breakwater is a barrier of rock or concrete built in the sea parallel to the coast, so that waves break on it before reaching the shore; sand often settles in the calmer water behind it. Breakwaters are expensive to build in open water, but they protect harbours and beaches without a wall on the shore itself; their main side effect is that the sand trapped behind them no longer moves downdrift.

Tetrapods, interlocking four-legged concrete blocks of several tonnes, armour many breakwaters and sea walls in Japan, the Mediterranean and India, because their legs lock together and leave gaps that absorb wave energy. On the Gold Coast of Australia, the submerged Narrowneck artificial reef works in the same way as a breakwater and holds sand on the beach.

Storm surge barriers

Where a large city lies on an estuary, a storm surge barrier can close the mouth of the estuary when a surge is forecast and stay open the rest of the time for ships and river flow.

• Thames Barrier, London (1982). Ten steel gates rotate up from the riverbed when high tides and surges threaten central London. It cost about £535 million and was designed against a 1-in-1,000-year surge to 2030. Expected to close two or three times a year, it made 221 flood defence closures by July 2026 and is planned to operate until about 2070.

• Maeslantkering, Rotterdam (1997). Two floating gates, each 210 m long, swing across the 360 m wide channel to the Port of Rotterdam when a 3 m surge is forecast, decided entirely by computer. It cost €450 million, first closed for a storm on 8 November 2007, and completed the Delta Works built after the 1953 flood.

Barriers protect huge areas for a fraction of the damage they prevent, but they depend on accurate forecasts and will close more often as the sea rises.

Costs and lifespans

Costs vary widely with exposure, materials and height, so the indicative ranges are used only for early comparisons of options.

Sources: Environment Agency, Cost estimation for coastal protection: summary of evidence (2015), using the Environment Agency unit cost database (2007 prices) and Crossman and Simm (2002).

Soft engineering

Soft engineering works with natural processes instead of resisting them. It adds or restores beaches, dunes, saltmarshes and mangroves that absorb wave energy, so that the coast protects itself. Soft schemes are usually cheaper, look natural and can create habitat, but they need repeating or maintaining and give a less certain standard of protection than a wall.

Beach nourishment and reprofiling

Beach nourishment (beach replenishment) adds sand or shingle, usually dredged offshore, to a beach. A higher, wider beach absorbs more wave energy, protects the cliffs or wall behind it and keeps the beach attractive for tourism. Because waves and longshore drift keep moving the sediment, nourishment must be repeated, typically every few years.

In 2011 the Netherlands’ Sand Motor (Zandmotor) placed 21.5 million m³ of sand in a hook-shaped peninsula of 128 ha south of The Hague, for about €70 million. Instead of nourishing the beach every 3–5 years, it lets waves, wind and tides spread the sand along the coast for 20 years or more, disturbing the seabed less often. Beach reprofiling and shingle recycling move sediment already on the beach back to where it was eroded; they are cheap but add nothing to the system.

Dune regeneration and natural defences

Dune regeneration rebuilds or stabilises dunes so they can store sand and block flooding: planting marram grass, fencing areas to keep people off, laying boardwalks, and thatching bare sand with brushwood to trap blown sand. Costs are very low, roughly £2–20 per metre for fencing or thatching, but dunes take years to recover and need space to move inland as the sea rises.

Healthy saltmarsh in front of a flood bank reduces wave height, so the bank can be lower and cheaper. Creating saltmarsh and replanting mangroves in the tropics are therefore treated as defences in their own right, often called nature-based solutions.

Cliff stabilisation

Many cliffs fail through wave erosion at the foot combined with mass movement higher up. Rain soaks into the rock, raises the water pressure in its pores and lubricates surfaces along which slumps and slides occur. Cliff stabilisation tackles both parts of the problem: toe protection with rock armour or a revetment, regrading the cliff to a gentler angle, drainage to let groundwater out, rock bolts and netting to hold loose blocks, and vegetation to bind the surface.

Stabilisation can secure cliff-top towns, but eroding cliffs are an important source of sediment for beaches and spits downdrift. Where they are stabilised that supply stops, and beaches further along may thin, so stabilising one cliff can raise erosion risk elsewhere in the sediment cell.

Managed retreat and no active intervention

Holding the coastline in place everywhere is neither affordable nor, as the sea rises, possible. Managed retreat, called managed realignment in the United Kingdom, deliberately moves the line of defence inland, often by breaching an old embankment and building a new one further back. The land in between floods with the tide and becomes saltmarsh or mudflat, which absorbs wave energy and protects the new defence.

At Medmerry, near Selsey in West Sussex, a shingle bank and 1960s embankment were repeatedly breached, flooding farmland, caravan parks and roads. In 2013 the Environment Agency completed a new 7 km floodbank inland and let the sea through the shingle bank. The £28 million scheme was the largest open-coast managed realignment in Europe when built; the flooded land became an RSPB reserve, and homes behind it gained a higher standard of protection.

No active intervention means that no money is spent on building or maintaining defences, and the coast is left to erode or flood. It is chosen where land is of low value, where defences would cost more than the assets they protect, or where eroding cliffs supply sediment to the rest of the coast. It is cheapest for the state, but the costs fall on the people who own land on that stretch.

Happisburgh, on the soft cliffs of north-east Norfolk, shows what a change of policy means for residents. When its 1959 timber defences decayed, the cliff retreated by 50 m between 1996 and 1999. The 2012 shoreline management plan changed Happisburgh’s policy from holding the line to managed realignment, and 35 homes were lost between 1988 and 2025. In a pilot scheme from 2009 to 2011, the council bought nine properties at 40% of their market value and demolished them.

Making coastal management decisions

Choosing between defence, retreat and doing nothing is a political and economic decision as much as a technical one, because the people who pay are not always the people who benefit. Most countries now use formal planning frameworks that look at the whole coast over the long term.

Shoreline management plans

In England and Wales each sediment cell or sub-cell has a shoreline management plan (SMP) that sets a policy for every stretch of coast for three periods: up to 20 years, 20–50 years and 50–100 years. There are four policies: hold the line (keep the shoreline where it is with defences, used for towns and infrastructure), advance the line (build seaward, rare), managed realignment (as at Medmerry) and no active intervention (undeveloped coast).

SMPs make the sediment cell, rather than the council boundary, the unit of planning, and they make the long-term future visible to residents. Their weakness is that they are not legally binding or tied to guaranteed funding, so a policy of holding the line can still fail if no money is found.

Cost–benefit analysis

A cost–benefit analysis compares the total cost of a scheme over its life with the value of the losses it prevents. A scheme is usually funded only if the benefits clearly exceed the costs.

Cost–benefit analysis makes decisions consistent and transparent, but it values things with a market price (houses, crops) more easily than heritage, a view or a sense of community, and it favours places where property is expensive. Two villages at equal risk can receive different decisions because their houses are worth different amounts, which raises questions of equity.

Environmental impact assessment and ICZM

Large schemes also need an environmental impact assessment, a formal study of their likely effects on habitats, sediment movement and water quality before permission is given. Integrated coastal zone management (ICZM) goes further: it brings together government departments, councils, ports, fishers, tourism businesses, conservation groups and residents so that defence, development, fishing, tourism and conservation are planned together across land and sea. The European Union recommended it to member states in 2002. It treats the coast as one system and gives weaker groups a voice, but it has no power of its own to stop a powerful developer or ministry.

Who decides and who pays

Evaluating hard and soft approaches

Hard engineering remains the only realistic option where cities, ports and critical infrastructure sit at the shoreline, as in London, Rotterdam or Jakarta. Soft engineering is better value on most beach and dune coasts, where it protects without moving the problem elsewhere. Managed retreat is the most sustainable option in the long term on low-value land, but it is socially the hardest, because a few people bear losses so that the wider coast and the public purse benefit. As the sea rises, the length of coast that can be defended at reasonable cost will shrink, and more coasts are likely to move from holding the line towards realignment.

Conflicting land-use pressures on coastlines

Coasts offer flat land, ports, fish, cooling water and the beaches that drive tourism, and many of the largest cities, from Shanghai to Lagos, grew as ports. The pressures on coastal land include:

• Tourism and second homes: hotels, resorts and marinas cluster at the shoreline, often on dunes or cliff tops, raising land prices.

• Ports and industry: container ports, refineries, gas terminals and nuclear power stations take large areas and alter sediment movement.

• Housing and urbanisation: growing cities spread along the shore and onto wetlands; in many cities of low- and middle-income countries the poorest households live in informal settlements on the lowest, most flood-prone land.

• Aquaculture: fish and shrimp ponds replace mangroves and saltmarsh on tropical coasts.

• Conservation: national parks and marine reserves protect habitats and so restrict all the other uses.

Where flat land is scarce, it is made. Land reclamation creates new land from the sea or from wetlands by draining or filling them. Singapore grew by about 25%, from 581.5 km² in 1960 to 725.7 km² in 2019, mostly through reclamation for housing, the airport and industry. Dubai’s Palm Jumeirah, begun in 2001 for luxury homes and hotels, had over 25,000 residents by 2022.

A conflict matrix

A conflict matrix sets each land use against every other one to show which pairs can share a stretch of coast and which cannot, helping planners decide which uses must be separated.

The matrix shows which uses clash, not who wins. Outcomes depend on power: capital to invest, backing from national government, legal ownership and the ability to be heard. Port authorities and developers usually have capital and political support; fishers, informal residents and wildlife usually do not. At Abbot Point in Queensland, a coal port expansion was approved in 2014 with a plan to dump about 3 million m³ of dredged seabed inside the Great Barrier Reef Marine Park; after protests by tourism operators, scientists and conservation groups, the spoil was moved to land and in 2015 the federal government banned dumping of such dredge spoil in the Marine Park.

Conservation measures and coastal planning

Governments control coastal development with protected areas (national parks, marine reserves, Ramsar sites, World Heritage Sites), setback lines, coastal zoning and ICZM. A setback line keeps new building a fixed distance from the shore. Setback lines are cheap and avoid the need for defences later, but they are hard to apply where buildings already stand, and landowners resist them because they lower land values.

Spain’s Coastal Law (Ley de Costas) of 1988 made the shore public property and set a protection zone, normally 100 m inland, in which new building is restricted; a 2013 reform reduced it to 20 m in some areas that were already built up, after pressure from owners of homes built before 1988.

Coastal zoning gives each activity its own space: a port where dredging does least harm, tourism on resilient beaches, and dunes, marshes and reefs as conservation zones. The Great Barrier Reef Marine Park is the best-known example of zoning at sea.

Stakeholders on the Gold Coast, Queensland

The Gold Coast is a city of about 690,000 people (2025 estimate) along 70 km of sandy coast in south-east Queensland, Australia. About 10 million visitors a year come for its surfing beaches, theme parks and high-rise resorts such as Surfers Paradise, and tourism is its largest industry. In 1967 a series of eleven cyclones removed most of the sand from its beaches and exposed beachfront buildings built on the frontal dunes. The response, based on a 1971 report by engineers from Delft University, has shaped every stakeholder’s role since.

The map shows that the coast works as one sediment system. Sand moves north from the Tweed River towards the Seaway, so the bypassing scheme in the south supports the beaches of Coolangatta, Burleigh Heads and Surfers Paradise, and each stakeholder’s interest depends on what happens to the sand further south.

The groups with the most capital, the developers and the state, secured a defended, nourished shoreline that supports high property values, but they also carry most of the cost. Residents and surfers with little money still changed decisions through campaigns, and undeveloped land was left to natural processes.

Sources: Australian Bureau of Statistics (2025 estimate); City of Gold Coast shoreline management documents, as summarised in Wikipedia’s Gold Coast articles (accessed 2026).

Managing coral reefs and mangrove swamps

Mangroves

A mangrove is a salt-tolerant tree or shrub of the intertidal zone on sheltered, muddy tropical and subtropical coasts, estuaries and deltas. Mangrove forests (mangrove swamps) covered about 137,600 km² in 118 countries and territories in 2010.

Mangroves provide many ecosystem services: dense roots reduce wave height and slow storm surges; sheltered channels are nurseries for fish, crabs and shrimp; communities take timber, fuelwood and honey; and waterlogged mangrove soils store large amounts of carbon, about 4.19 billion tonnes worldwide in 2012. Carbon held in coastal and marine ecosystems is called blue carbon, and it is released as carbon dioxide when mangroves are cleared.

Mangroves are cleared mainly for shrimp and fish ponds, rice fields, oil palm, resorts and urban growth. Losses were fastest in the late twentieth century: world mangrove area fell from about 188,000 km² in 1980 to 152,000 km² in 2005, about a fifth, with the largest losses in Asia, where shrimp ponds replaced mangroves in Indonesia, Thailand, Vietnam and the Philippines. Clearance has since slowed, and global mangrove area fell by a net 3,700 km² between 1999 and 2019, with annual losses of up to 0.7% in some countries.

Sources: FAO, The world’s mangroves 1980–2005 (2007); Global Mangrove Watch, as reported in Wikipedia’s Mangrove article (accessed 2026).

Coral reefs

A coral reef is built from the calcium carbonate skeletons of coral polyps in warm, shallow, clear, nutrient-poor tropical water; the corals depend on zooxanthellae, algae in their tissues that supply food by photosynthesis. Reefs hold a large share of marine species, break waves and support fisheries and tourism. They face global threats, marine heatwaves that cause coral bleaching and ocean acidification that slows skeleton growth, together with local ones: overfishing and blast fishing, sediment and fertiliser runoff that feeds outbreaks of the coral-eating crown-of-thorns starfish, anchors and trampling, and coral mining.

How reefs and mangroves are managed

• Marine protected areas and no-take zones. A marine protected area (MPA) restricts human activities by law; a no-take zone inside it bans all fishing and collecting. Protected fish grow larger and spill over into fished areas nearby.

• Community-based management. In Fiji, Locally Managed Marine Areas let villages set temporary closures (tabu areas), gear limits and seasons using customary authority.

• Mangrove replanting. It restores protection and fisheries, but many projects fail because seedlings are planted on mudflats or in places flooded too often or too rarely, or with one fast-growing species.

• Payment for ecosystem services. Under payment for ecosystem services, those who benefit from an ecosystem (a government, a tourism company, buyers of blue carbon credits) pay those who manage it to keep it intact.

• Reef restoration. Reef restoration grows coral fragments in nurseries and transplants them, or fixes rubble so corals can settle. It helps small areas but is slow and costly.

• Catchment management. Cutting the fertiliser, soil and sewage that reach the sea from land is as important as rules at sea.

Detailed example: the Great Barrier Reef, Australia

The Great Barrier Reef has over 2,900 reefs and 900 islands stretching more than 2,300 km along Queensland’s coast over about 344,400 km²; it became a World Heritage Site in 1981. Tourism, mainly diving, snorkelling and boat trips from Cairns, Port Douglas and the Whitsundays, is its largest commercial use.

Its average coral cover fell by about half between 1985 and 2012, mainly through tropical cyclones and outbreaks of crown-of-thorns starfish, and mass bleaching in 1998, 2002, 2016, 2017, 2020, 2022, 2024 and 2025 has since left little time for recovery. More than 90% of the pollution reaching it from rivers, its largest source of nutrients, comes from farms, mainly sugar cane and grazing.

The Great Barrier Reef Marine Park (1975) is managed by zoning; a 2004 plan raised the share in no-take zones from 4.5% to over 33%. The Reef 2050 Plan (2015, updated 2021) targets water quality, starfish control and restoration, and after UNESCO’s 2022 mission recommended an “in danger” listing, the government promised A$4.4 billion and an end to gill-net fishing by 2027.

Scientists argue that only deep cuts in greenhouse gas emissions can stop repeated bleaching; the coal and farming industries argue for development, and commercial fishers oppose the gill-net ban. Local management can improve water quality, but ocean temperature is decided at the global scale.

Sources: Great Barrier Reef Marine Park Authority; UNESCO World Heritage Centre (2022); Australian Government letter to UNESCO (May 2023), as reported in Wikipedia (accessed 2026).

Detailed example: the Sundarbans, Bangladesh and India

The Sundarbans, the world’s largest mangrove forest, covers about 10,000 km² of the Ganges–Brahmaputra–Meghna delta, about 60% in Bangladesh and 40% in India, and each country’s part is a World Heritage Site. It is one of the last large habitats of the Bengal tiger and supports millions of villagers who collect fish, crabs, honey and wood. It is also a cyclone barrier: Cyclone Sidr damaged about 40% of the forest in 2007, but the forest absorbed much of the surge that would have reached villages inland.

Sea-level rise and reduced freshwater flow, partly linked to India’s Farakka Barrage upstream, are raising salinity, and shrimp farms press on its edges. The coal-fired Rampal power station, a project of Bangladesh’s Power Development Board and India’s NTPC agreed in 2010 and sited 14 km north of the forest, was criticised by UNESCO in 2016 and by groups citing the Ramsar Convention, while the Bangladeshi government argued that the country needed electricity. Because the forest, the river that feeds it and the threats to it cross the border, neither government can protect it alone.

Sources: UNESCO World Heritage Centre, as reported in Wikipedia’s Sundarbans article (accessed 2026).

Sovereignty and maritime zones

Sovereignty is the supreme authority of a state over its territory. At sea, how far that control extends matters because the sea holds fish, oil, gas and minerals and carries trade and navies. The rules are set by the United Nations Convention on the Law of the Sea (UNCLOS), agreed in 1982 and in force since 1994, which has 172 parties, including 168 UN member states and the European Union. The United States has not ratified it, although it follows most of its navigation rules in practice.

The zones

All zones are measured from the baseline, normally the low-water line on official charts; along deeply indented coasts or fringing islands, straight baselines may join headlands or islands. Waters landward of the baseline (bays, estuaries, harbours) are internal waters under full state control.

A state does not own the water of its EEZ and cannot stop ships passing, but it alone decides who may fish, drill or mine there. Where the continental shelf runs beyond 200 nm, a state can claim seabed rights up to 350 nm by sending evidence to the UN Commission on the Limits of the Continental Shelf, which in 2008 confirmed Australia’s rights over an extra 2.5 million km². In the Arctic, Russia, Denmark (for Greenland) and Canada have made overlapping submissions for the seabed around the North Pole, including the Lomonosov Ridge, because retreating sea ice is making its resources easier to reach.

Islands, rocks and boundaries

Every island generates its own territorial sea and EEZ. Kiribati has only 811 km² of land, but its 33 islands spread across about 3.4 million km² of the Pacific, earning income from licences sold to foreign tuna fleets. France, through its overseas territories, has an EEZ of about 10.2 million km², around 7% of the area of all EEZs.

UNCLOS distinguishes islands from rocks: a feature that cannot sustain human habitation or economic life of its own gets only a 12 nm territorial sea. Japan has encased the two rocks of Okinotori, with under 10 m² of dry land, in concrete and claims an EEZ around them; China, South Korea and Taiwan reject the claim. In 2016 an arbitral tribunal ruled that none of the Spratly Islands in the South China Sea can generate an EEZ. Where coasts are less than 400 nm apart, the EEZs overlap and the states must agree a boundary, usually a median line equidistant from the two baselines.

Case study: Jakarta, subsidence, sea walls and moving a capital

Jakarta, the capital of Indonesia, lies on the north-west coast of Java at the mouth of the Ciliwung River, facing Jakarta Bay and the Java Sea. The province covers about 664 km² and had about 11 million registered residents in 2025, while the United Nations estimated the population of the wider urban area at 41.9 million. It is built on a low alluvial plain that was once swamp, crossed by 13 rivers, and about 40% of it, mainly in the north, now lies below sea level.

The process: a city sinking faster than the sea is rising

Jakarta’s coastal flood risk is driven mainly by the sinking of the land, and only partly by sea-level rise. The city is sinking through land subsidence, mainly because of the pumping of groundwater from the aquifers beneath the city: as water is removed, the fine clay and silt layers compact and the ground drops. The weight of buildings adds to the compaction. Households and businesses pump their own groundwater because the piped network has for decades been incomplete and expensive; in 2026 the city water company PAM Jaya still did not reach every household.

The National Research and Innovation Agency (BRIN) estimated in January 2026 that the city as a whole is sinking by about 3.5 cm a year, and that parts of North Jakarta have dropped by as much as 4 m in four decades. Other estimates for the north give 5–10 cm a year, ten to twenty times the rate of global sea-level rise.

As the ground sinks, seawater flows into low-lying districts at high tide (tidal or rob flooding), river water can no longer drain to the sea by gravity, and pumps must lift it over embankments. Monsoon rain, blocked drains and urban growth upstream add river floods. In 2007 about 70% of the city was flooded, up to 4 m deep in places, and about 80 people died. BRIN estimates that floods cost Jakarta at least US$186 million a year, rising to US$421 million by 2030 if subsidence continues.

The decisions and the actors

Three responses have been debated, each favoured by different actors with very different amounts of power.

• 1. Walls and reclamation: the National Capital Integrated Coastal Development (NCICD). A master plan drawn up by the Indonesian government with Dutch firms. Phase A strengthens and raises the existing coastal embankments; later phases would build a giant offshore sea wall across Jakarta Bay enclosing a lagoon to store river water, with 17 artificial islands for offices, housing, a port and toll roads. The full plan was estimated at about US$40 billion.

• Construction began on 9 October 2014; by January 2026 only about 20 km of the 46 km NCICD embankment had been built.

• 2. Stopping the cause: controlling groundwater. In 2021 the governor banned groundwater extraction in nine industrial areas and along 12 roads, and the city is extending piped water. Scientists at BRIN and the National University of Singapore argue that without stopping groundwater pumping, any wall will only buy time, because the land behind it will keep sinking.

• 3. Moving the seat of government: Nusantara. In August 2019 President Joko Widodo announced that the capital would move to a new city in East Kalimantan, on the island of Borneo. Nusantara is planned in five phases to 2045 at an estimated Rp 523 trillion (about US$35 billion). Indonesia held its Independence Day there for the first time on 17 August 2024. Jakarta remains the capital until a presidential decree formally transfers the role.

The outcomes have been uneven. The embankments that have been built have reduced tidal flooding compared with unprotected coasts elsewhere in Java, such as Demak. But the poorest residents, nearest the sea and most reliant on groundwater, face the highest risk, while reclaimed land would mainly benefit investors. Critics argue that the public pays for the walls while developers take the profits.

What the case shows

Jakarta shows that coastal decisions are rarely about the coast alone. The most effective long-term measure, replacing groundwater with piped water, is a question of urban water supply and equity, while the most visible measures, walls and a new capital, attract investment and attention. Nusantara is planned to house government ministries, while Jakarta’s residents and its main port, Tanjung Priok, will still depend on defences that must be raised as the land sinks.

• To what extent is the Jakarta sea wall a sustainable solution to the city’s flood risk?

• Which stakeholders gain most from the NCICD plan, and which lose most? Explain why.

• Suggest why controlling groundwater use has proved harder to achieve than building embankments.

Sources: BRIN, reported by Asia News Network (2026); Indonesia Water Portal (2023); Statistics Indonesia and UN DESA, as reported in Wikipedia’s Jakarta article (2025); Wikipedia: Floods in Jakarta, Giant Sea Wall Jakarta and Nusantara (accessed 2026).

Exam practice

Structured question

The map and table show part of a hypothetical shoreline management plan for a 30 km stretch of eroding coast. Study them and answer the questions.

Extended response

Summary

• Defences in one place can increase erosion elsewhere in the same sediment cell.

• Hard engineering gives strong protection at high cost, with side effects such as toe scour and sediment starvation downdrift.

• Soft engineering works with natural processes but must be repeated or maintained.

• Cliff stabilisation secures cliff tops but can cut off sediment supply to other beaches.

• Managed retreat and no active intervention are cheaper and more sustainable in the long term but transfer losses to landowners.

• Shoreline management plans, cost–benefit analysis and ICZM structure decisions; power, money and compensation decide who gains and who loses.

• Conflict matrices, protected areas, setback lines and zoning help manage competing coastal land uses, as on the Gold Coast.

• Reefs and mangroves are managed through protected areas, no-take zones, community management, replanting, restoration and payments for ecosystem services.

• UNCLOS gives sovereignty to 12 nm, limited control to 24 nm and resource rights to 200 nm; islands, rocks and sea-level rise make zones contested.

• In Jakarta, groundwater-driven subsidence drives flood risk; walls, groundwater controls and a new capital reflect very differently placed actors.

Self-check

• To do:

  I can describe how sea walls, revetments, rock armour, gabions, groynes, offshore breakwaters and storm surge barriers work, with costs and side effects.

• To do:

  I can explain how beach nourishment, dune regeneration, cliff stabilisation and managed retreat work, with named examples.

• To do:

  I can examine how shoreline management plans, cost–benefit analysis and ICZM are used to make coastal decisions.

• To do:

  I can determine a benefit–cost ratio and use it to compare two coastal management options.

• To do:

  I can evaluate hard and soft approaches from the perspectives of different stakeholders.

• To do:

  I can explain coastal land-use conflicts using a conflict matrix and the Gold Coast example.

• To do:

  I can discuss the value, threats and management of coral reefs and mangroves, using the Great Barrier Reef and the Sundarbans.

• To do:

  I can outline the UNCLOS maritime zones and convert nautical miles to kilometres.

• To do:

  I can evaluate the outcomes of coastal management in Jakarta for different groups of people.

Good answers may be well structured (AO4) and may additionally offer a critical evaluation (AO3) which examines how the distribution of costs and benefits depends on governance, eg Norway's state ownership and sovereign wealth fund spread oil benefits widely, unlike states with weak institutions (places, power). Another approach might be to consider different scales: a national gain may hide local losses (scale), or to discuss how international law (UNCLOS, ISA rules, the polluter-pays principle) attempts to share benefits and costs more fairly (possibilities, equity).

For 5–6 marks, expect some weakly-evidenced outlining of costs and/or benefits of abiotic resource use for one or more groups.

For 7–8 marks, expect a structured account which includes:

• either well-evidenced explanation of how costs and benefits are distributed between different places and/or people

• or a discursive conclusion (or on-going evaluation) of the extent of inequality grounded in geographical concepts and/or perspectives.

For 9–10 marks, expect both of these traits.

NB. Maximum [4] if the answer only discusses biotic resources.

Markbands (10 marks, 2 marks per band)