Beach erosion is the long-term process by which coastal sediments, primarily sand, are removed from a beach system. This phenomenon is driven by waves, tides, and storm surges, and accelerated by human activities like coastal development. When sediment loss exceeds replenishment, the shoreline retreats, threatening infrastructure and natural habitats. Protecting coastlines requires implementing varied strategies, from physical structures to methods that stabilize the shore naturally.
Hard Coastal Engineering Structures
Combating erosion often involves constructing rigid, fixed structures known as hard coastal engineering. These structures interrupt the natural movement of water and sediment along the shoreline. Groynes are common examples, built as narrow barriers extending perpendicularly from the beach into the water.
The function of a groyne is to trap sediment transported by the longshore current, which moves sand parallel to the coast. By interrupting this flow, the structure encourages sand accumulation on the up-current side, widening the beach. This wider beach serves as a natural buffer, absorbing wave energy. Groynes are constructed from durable materials like timber, concrete, or rock armor for long-term use.
However, trapping sediment deprives down-drift beaches of their natural sand supply, often accelerating erosion in those areas. Other hard structures, like seawalls and revetments, are built parallel to the shore to protect property and infrastructure from storm waves. These structures reflect wave energy, which can lead to the scouring and loss of sand directly at the base of the wall. Jetties are similar to groynes but are larger, permanent structures built at harbor entrances or inlets to prevent navigation channels from silting up.
Beach Nourishment and Sand Replenishment
Soft engineering methods introduce new sediment into the coastal system rather than relying on fixed structures. Beach nourishment, also called replenishment, involves artificially placing large volumes of sand onto an eroded beach to increase its width and elevation. This wider beach face dissipates wave energy and provides storm protection for the land behind it. Nourishment is considered a non-permanent solution because it does not address the underlying causes of erosion.
The process begins by sourcing compatible sediment, usually dredged from offshore areas. Compatibility is important; the imported sand must closely match the native material in grain size, composition, and color to ensure stability. Specialized vessels, such as hopper or pipeline dredges, suction the sand from the borrow site and pump the mixture through pipes directly onto the targeted beach.
Once the sediment is placed, heavy machinery spreads and shapes it to the desired profile. Since the forces causing the initial erosion remain active, the newly placed sand will inevitably erode again. Nourishment projects must therefore be repeated, often requiring new applications every two to ten years. Despite being temporary, beach nourishment remains popular because it preserves the recreational and aesthetic value of a wide sandy beach.
Biological and Dune Stabilization Techniques
The third approach stabilizes the coastal landscape using vegetation and ecological management. This method centers on the health of foredunes, which function as the coast’s first line of natural defense. Sand dunes provide a flexible barrier that absorbs the impact of high-energy waves and storm surges.
Dune stability depends on specialized vegetation, such as native dune grasses, which thrive in the harsh coastal environment. These plants trap wind-blown sand, encouraging the natural growth and heightening of the dune over time. Deep, layered root systems physically bind the surface sand particles together, making the dune resistant to wind erosion and wave action.
Biological stabilization involves planting appropriate native species and using sand fencing or biodegradable materials to initiate sand accumulation. Protecting existing vegetation is equally important, as human activity like foot traffic can damage the plants. This damage creates gaps or “blowouts” that destabilize the entire dune system. Maintaining a healthy, vegetated dune system ensures the coast retains a natural sand reservoir that can temporarily replenish the beach face after a severe storm.