A seawall (or sea wall) is a form of coastal defense constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a seawall is to protect areas of human habitation, conservation and leisure activities from the action of tides, waves, or tsunamis. As a seawall is a static feature it will conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea. Seawall designs factor in local climate, coastal position, wave regime (determined by wave characteristics and effectors), and value (morphological characteristics) of landform. Seawalls are hard engineering shore-based structures which protect the coast from erosion. Various environmental issues may arise from the construction of a seawall, including the disruption of sediment movement and transport patterns. Combined with a high construction cost, this has led to an increasing use of other soft engineering coastal management options such as beach replenishment. Seawalls are constructed from various materials, most commonly reinforced concrete, boulders, steel, or gabions. Other possible construction materials include vinyl, wood, aluminum, fiberglass composite, and biodegradable sandbags made of jute and coir. In the UK, seawall also refers to an earthen bank used to create a polder, or a dike construction. The type of material used for construction is hypothesized to affect the settlement of coastal organisms, although the precise mechanism has yet to be identified. Types A seawall works by reflecting incident wave energy back into the sea, thus reducing the energy available to cause erosion. Seawalls have two specific weaknesses. Wave reflection from the wall may result in hydrodynamic scour and subsequent lowering of the sand level of the fronting beach. Seawalls may also accelerate erosion of adjacent, unprotected coastal areas by affecting the littoral drift process. Different designs of man-made tsunami barriers include building reefs and forests to above-ground and submerged seawalls. In 2005, India began planting Casuarina and coconut saplings on its coast as a natural barrier against future tsunamis like the 2004 Indian Ocean earthquake. Studies have found that an offshore tsunami wall could reduce tsunami wave heights by up to 83%. The appropriate seawall design relies on location-specific aspects, including surrounding erosion processes. There are three main types of seawalls: vertical, curved or stepped, and mounds (see table below). Natural barriers A report published by the United Nations Environment Programme (UNEP) suggests that the tsunami of 26 December