Coastal Management Strategies and Case Study

Why coastlines need management

Coastal erosion removes land, while coastal flooding covers land with seawater. Both can threaten homes, roads, businesses and habitats. Management aims to reduce these risks, but protecting one stretch of coastline can change conditions elsewhere.

A beach is itself a form of protection: waves lose energy as they travel across it, so a wider beach can reduce the energy reaching the land behind. This explains why some strategies protect the shore directly, while others aim to maintain beaches or dunes.

Deciding what to protect involves more than choosing the strongest defence. Managers weigh construction and maintenance costs against the value of threatened property, infrastructure, livelihoods and environments. They also consider who benefits and who may lose out. A sustainable scheme needs to remain useful over time without creating unacceptable problems elsewhere.

Hard engineering: protecting the shore with structures

Hard engineering uses built structures to resist coastal erosion or flooding. Different structures work in different ways, so their benefits and limitations are not interchangeable.

Sea walls are usually concrete barriers built along the shore to protect the land behind from erosion and flooding. A recurved face reflects waves back towards the sea, helping prevent them from reaching the land. Sea walls provide strong, long-lasting protection where wave energy is high, so they can be suitable for valuable settlements and infrastructure. Bridlington on the Holderness Coast, for example, has a 4.7 km sea wall. A promenade on top can also provide space for walking and recreation.

However, sea walls are expensive to build and maintain. Reflected waves can scour—erode and remove—beach material at the wall's base, potentially undermining its foundations. This means that protecting the land does not necessarily protect the beach in front. High waves can still overtop the wall and cause flooding. Sea walls can also restrict beach access, damage coastal habitats and look unnatural. Their strength must therefore be weighed against their financial and environmental costs.

Rock armour, also called riprap, consists of large boulders piled along the shore, often at the foot of cliffs or sea walls. The rocks absorb wave energy, reducing its impact on the coast. It is relatively cheap to construct compared with some other substantial defences, but powerful storms can erode or dislodge the boulders, requiring repairs.

Gabions are wire cages filled with stones, placed at the foot of cliffs or sea walls. They absorb wave energy and are a relatively inexpensive defence. However, the cages can break and must be securely tied down. Their lower cost comes with limitations in strength and effectiveness compared with more substantial structures.

Groynes are barriers of wood, rock or steel built at right angles to the shore. They trap sand and shingle being transported by longshore drift. The trapped material builds a wider beach, which absorbs wave energy and helps reduce erosion. A larger beach can also benefit recreation and tourism.

The disadvantage is that sediment retained at one beach is no longer available to beaches farther along the direction of drift. These beaches may become narrower and less able to protect the land behind. Wooden groynes also need maintenance to prevent decay, and the barriers can make walking along the shoreline difficult.

The important connection is between sediment supply and protection: a groyne may benefit the defended stretch while increasing erosion farther along the coast. Its success therefore needs to be judged across a wider area, not just beside the structure.

Soft engineering: maintaining natural protection

Soft engineering works with natural processes rather than relying mainly on substantial built barriers. It often keeps the coast looking more natural, but still involves intervention, expense and maintenance.

Beach nourishment adds sand or shingle to replace material lost through erosion. A wider beach absorbs more wave energy before waves reach the land behind. It also preserves a beach for visitors, supporting tourism. However, waves and longshore drift continue to move the added sediment, so nourishment must be repeated. This increases long-term costs. Obtaining sediment from the seabed can damage marine ecosystems, while machinery can temporarily disrupt beach use.

Beach reprofiling redistributes existing sand and shingle to change the shape of the beach. Sediment can be moved from the lower beach to the upper beach to restore its protective profile. Unlike nourishment, its main purpose is to rearrange material rather than add a new supply. It is relatively simple, retains a natural appearance and can improve the beach's ability to reduce wave energy. However, moving sediment can disturb wildlife, restrict public access during the work and require frequent repetition. It is less suitable for very high-energy conditions.

Dune regeneration restores and stabilises sand dunes. Planting vegetation such as marram grass helps hold sand in place and reduces wind erosion. Fencing and controlled access protect the vegetation from trampling and allow dunes to recover. The dunes form a natural barrier between the sea and the land, absorbing wave energy and reducing erosion and flooding.

Dune regeneration can be relatively inexpensive and retains a natural landscape. However, recovery takes time, storm waves can damage the dunes, and closing areas to the public can be unpopular. It also depends on suitable dune environments: it cannot provide the same protection along every type of coastline, particularly extensive cliffs.

Managed retreat: allowing planned coastal realignment

Managed retreat, or coastal realignment, accepts that keeping the present coastline in place may be too costly or unsuitable. Existing defences are removed or abandoned so that the sea can flood selected land. The coastline moves inland towards higher ground or a new line of defences. People and infrastructure may need to be relocated.

Where conditions allow, the flooded land develops into salt marsh. This creates habitats and provides a natural buffer that reduces wave energy before it reaches the land farther inland. Realignment can reduce the need to keep defending the original shoreline.

The benefits must be weighed against serious costs. Agricultural land, homes or livelihoods may be lost; relocation can be expensive; and saltwater changes existing ecosystems. Landowners and residents may oppose the scheme, especially where compensation is uncertain. Managed retreat is therefore a planned response with winners and losers, not simply an absence of management.

UK example: management at Mappleton on the Holderness Coast

The Holderness Coast lies on the east coast of Yorkshire, extending about 61 km from Flamborough Head to Spurn Head beside the Humber Estuary. Much of its vulnerable coastline consists of soft boulder clay. Narrow beaches provide limited protection, while North Sea waves have a long fetch—the distance over which wind can generate waves—and can reach the coast with considerable energy. Coastal retreat threatens settlements and roads.

At Mappleton, management was needed to protect the village and the B1242 road from erosion. Rock armour costing about £2 million was used, together with groynes and beach nourishment. These methods complement one another: rock armour absorbs wave energy directly, while groynes retain sediment and nourishment helps build the protective beach.

The scheme produced a sandy beach and reduced the erosion threat to Mappleton and the road. This is a clear local benefit: management protected a settlement and an important transport route rather than allowing continued retreat.

Resulting effects and conflicts

Longshore drift carries sediment southwards along this coast. The groynes at Mappleton retain some of that material, reducing the supply reaching beaches farther south. With less beach protection, Great Cowden experienced increased erosion, including the loss of farmland.

This creates a conflict between people benefiting from protection at Mappleton and those facing greater losses elsewhere. Residents and landowners may disagree over which places receive defences and whether protecting one community justifies increasing risks to another.

Mappleton therefore shows why a scheme can be locally successful without solving the problems of the whole coastline. A balanced judgement recognises the protection of the village and B1242, the construction and maintenance commitment, and the adverse effects of sediment trapping farther south. The most suitable approach depends on both the value of what is protected and the wider consequences of changing coastal processes.

Hard engineering

Soft engineering

• Nourishment: adds sand or shingle; maintains a protective beach, but needs repeated expenditure and can damage sediment-source habitats.
• Reprofiling: redistributes sediment to restore beach shape; relatively simple, but repeated work disturbs wildlife and beach access.
• Dune regeneration: vegetation and controlled access stabilise dunes; natural protection, but slow recovery, storm damage and access restrictions.

Managed retreat

Allow planned inland movement of the coastline by removing or abandoning defences. Salt marsh can provide habitats and a natural buffer, but land and livelihoods may be lost and relocation can be costly.

Mappleton, Holderness Coast

• Why: soft boulder clay, narrow beaches and energetic North Sea waves threatened the village and B1242 road.
• Methods: about £2 million of rock armour, plus groynes and beach nourishment.
• Benefits: sandy beach; reduced erosion threat to village and road.
• Conflict: groynes interrupt southward sediment transport → less beach protection at Great Cowden → increased erosion and farmland loss.
• Judgement: local protection must be weighed against long-term costs and effects elsewhere.