Coastal erosion is a natural process involving the wearing away and displacement of land along the shoreline. It is primarily driven by the physical actions of the ocean, including wave impact, tides, and strong currents. Storms and extreme weather events intensify this process, rapidly removing sand and rock. The long-term loss of sediment and land destroys coastal infrastructure and leads to the loss of beaches. Mitigation efforts are necessary to protect human communities and maintain coastal ecosystems.
Structural Solutions: Hard Engineering
Hard engineering involves constructing rigid, fixed structures designed to physically resist or deflect the sea’s energy. These methods aim to protect the land immediately behind them and are the most visible forms of coastal intervention. While they provide immediate protection for specific assets, they often have unintended consequences for the wider coastal system.
Seawalls and revetments are common structural defenses built parallel to the shore to shield the land from wave action. A seawall is typically a vertical concrete structure designed to reflect wave energy. A revetment is a sloped barrier made of loose material, such as large rocks (riprap), which absorbs and dissipates wave energy. Vertical seawalls often reflect incoming waves with force, scouring sediment at the base and causing the beach in front to narrow or disappear. This erosion can undermine the wall’s stability.
Groynes are structures built perpendicular to the coastline, extending into the water. Their function is to interrupt longshore drift, trapping sediment on the updrift side to widen the beach. The accumulated sand dissipates wave energy before it reaches the shore, stabilizing the immediate area. However, by preventing sediment movement, groynes often starve downdrift beaches, causing accelerated erosion. This transfer of erosion problems is a common drawback.
Detached breakwaters are constructed offshore, parallel to the coastline, typically using concrete units or rock piles. They reduce the height of incoming waves through reflection and dissipation, creating a calmer zone of lower wave energy between the structure and the shore. This sheltered area encourages sediment deposition, often forming a bulge of sand on the beach called a salient. If enough sediment accumulates, this feature may connect to the breakwater, forming a tombolo. Breakwaters are often segmented with gaps to allow water and sediment exchange, maintaining natural coastal processes.
Ecological Solutions: Soft Engineering
Soft engineering methods work with natural coastal processes, utilizing natural materials or enhancing existing environmental features to stabilize the shoreline. These solutions are considered more sustainable and ecologically friendly than hard structures. They aim to absorb wave energy and build natural buffers, often providing habitat benefits alongside erosion control.
Beach nourishment, or replenishment, is the most common soft engineering technique, involving the artificial placement of large volumes of sand onto an eroding beach. The added sand widens the beach, creating a larger buffer that forces waves to break farther offshore, dissipating their energy. Since this process does not stop underlying erosion, it requires periodic renourishment, typically every few years, to maintain protection. The imported sand must closely match the native sediment’s grain size to ensure it remains on the beach and avoids negatively impacting local ecosystems.
Dune restoration and stabilization focus on reinforcing the natural sand barriers that protect the coast from storms. This is achieved by planting native, salt-tolerant vegetation, such as American beachgrass or sea oats, whose extensive root systems bind the loose sand. Fences or specialized mats are often used temporarily to trap windblown sand and encourage initial accumulation, allowing vegetation to take hold. Healthy dune systems are flexible, naturally absorbing storm surge energy and providing a sand reservoir to replenish the beach during erosion events.
Living shorelines are an advanced soft solution that integrates natural elements like plants, sand, and rock to create a stabilized coastal edge. Used mostly in lower-energy environments such as estuaries and bays, these hybrid approaches involve planting marsh grasses and constructing submerged features like oyster reefs or rock sills. The vegetation and reefs work together to filter runoff, attenuate wave energy, and trap sediment, offering erosion control and enhanced aquatic habitat. Living shorelines promote long-term stability and resilience, becoming more robust as plant roots and biological structures grow.
Strategic Planning and Managed Retreat
Long-term coastal management increasingly incorporates strategic planning and policy-based solutions focused on adapting to coastal change rather than defending the current shoreline. These approaches, known as managed retreat or coastal realignment, represent a coordinated strategy to minimize human risk. They involve allowing the coastline to move naturally to a more sustainable position.
Managed retreat is the planned, phased withdrawal of people, structures, and infrastructure from high-risk coastal areas. Instead of building new defenses, this strategy allows the land to become naturally inundated, often by removing existing hard structures like seawalls. This process creates new intertidal habitats, such as salt marshes, which serve as a natural buffer against future storm events. While economically sound long-term, this approach is often contentious due to the social challenges of relocating communities.
Land use zoning and building regulations are proactive policy tools that limit or prohibit development in erosion-prone areas. Governments establish setback lines, which are predetermined distances from the shoreline where construction is restricted based on historical or projected erosion rates. Regulations may also mandate that new construction in high-risk zones be easily relocatable or structurally elevated to withstand flooding and erosion. These planning efforts aim to avoid future property loss and minimize the need for expensive, short-term engineering fixes.
Relocation assistance programs facilitate the voluntary movement of residents and businesses out of hazardous zones. These often take the form of government buyout programs, where at-risk properties are purchased and demolished. The acquired land is typically converted into open space or habitat restoration areas, permanently removing the risk and creating a natural buffer. This policy tool manages the transition and provides financial aid to property owners impacted by long-term safety strategies.