page_title: Coastal flooding
section_title: Engineered defences
hierarchical_section_title: Coastal flooding / Mitigation / Engineered defences
caption_attribution_description: English: Jordi Serra, EUROSION project
context_page_description: Coastal flooding occurs when normally dry, low-lying land is flooded by seawater. The extent of coastal flooding is a function of the elevation inland flood waters penetrate which is controlled by the topography of the coastal land exposed to flooding. The seawater can flood the land via from several different paths:
  Direct flooding — where the sea height exceeds the elevation of the land, often where waves have not built up a natural barrier such as a dune
  Overtopping of a barrier — the barrier may be natural or human engineered and overtopping occurs due to swell conditions during storm or high tides often on open stretches of the coast. The height of the waves exceeds the height of the barrier and water flows over the top of the barrier to flood the land behind it. Overtopping can result in high velocity flows that can erode significant amounts of the land surface which can undermine defense structures.
  Breaching of a barrier — again the barrier may be natural or human engineered, and breaching occurs on open coasts exposed to large waves. Breaching is where the barrier is broken down or destroyed by waves allowing the seawater to extend inland and flood the areas.
context_section_description: There are a variety of ways in which humans are trying to prevent the flooding of coastal environments, typically through so-called hard engineering structures such as seawalls and levees. That armouring of the coast is typical to protect towns and cities which have developed right up to the beachfront. Enhancing depositional processes along the coast can also help prevent coastal flooding. Structures such as groynes (Figure 1), breakwaters and artificial headlands promote the deposition of sediment on the beach thus helping to buffer against storm waves and surges as the wave energy is spent on moving the sediments in the beach than on moving water inland.
caption: (Figure 1) Groynes are engineered structures that aim to prevent erosion of the beach front
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