seawall

A seawall is a coastal defense structure built parallel to the shoreline to protect land and developments from waves, storm surge, and coastal erosion. Seawalls are typically constructed behind the beach or at the back of a floodplain and are designed to reflect or dissipate wave energy, reducing direct wave impact on the shore.

Types and materials: Common forms include concrete vertical or sloped walls, gravity walls, and rubble-mound revetments with a facing. Some are steel sheet-pile walls or timber sheet-pile structures; modern seawalls may be reinforced concrete with armor units, such as rock or precast blocks. They may include backfill and drainage features.

Function and design considerations: Design depends on wave climate, tidal range, water levels, and soil conditions. Key factors: overtopping, frequency, backshore protection, drainage, and foundation stability. Potential drawbacks: increased erosion elsewhere due to reflected energy, loss of beach, higher maintenance costs, potential seepage and undermining, and ecological impacts.

Construction and maintenance: Construction requires geotechnical assessment, proper foundation bearing, and drainage. Maintenance includes inspection, crack repair, armor replacement, and sediment management. Some seawalls incorporate sloping profiles or berms to promote overtopping rather than reflection and to preserve beaches.

History and context: Seawalls have been used for centuries in various forms and are a common element of urban coastlines. They are often part of larger coastal defense strategies that include breakwaters and groynes; in some settings, managed retreat or beach nourishment is considered preferable due to environmental and social impacts.