In 1735, the people of the French colony of Pondicherry, known today as Puducherry, constructed one of the first seawalls. It has been continually fortified over the years with boulders being added to fill in gaps whenever they appear. In 2004, the seawall kept Pondicherry's center safe when huge tsunami waves ravaged neighboring lands.
Seawalls are constructed to protect shorelines from flooding and erosion. They are a barrier between the coastline and the ocean to keep the shore from washing away. Seawalls also protect buildings and communities from flooding and storm damage. They can provide recreational space for people, such as fishing from or walking on the top of the wall.
Seawalls can be built from a number of different materials, including the most common of concrete, boulders or steel. Vinyl and wood may also be used to construct seawalls for additional support. Modern seawalls have a curved shape in order to deflect waves back to the sea. Some seawalls, however, are straight and designed to stop waves all together. The top of the seawall is flat, which creates a space for human traffic. Seawalls can vary immensely in height depending on their main purpose. Those built strictly to prevent flooding, for example, would be taller than those built mostly to prevent erosion. All seawalls extend from the shore and into the water to prevent waves from crashing on to the shore.
There are several types of seawalls which can be constructed based upon the needs of the area. Vertical seawalls are generally constructed in very exposed areas. They reflect waves. In severe storm situations, the walls can cause standing waves to develop. Curved seawalls, sometimes called stepped seawalls, are created to dissipate and repel waves back to the ocean. A series of mound-type structures known as revetments may also be employed as seawalls. They are used in less threatened areas of shoreline to minimize the effects of erosion and strengthen the shore.
Effective seawalls can be very expensive to construct. Poorly designed or inexpensively built seawalls require constant maintenance as waves erode the base. These cheaper seawalls are also more likely to fail in severe weather conditions. All seawalls will eventually require maintenance due to the constant beating waves. Very high waves can overcome some seawalls in the case of tsunamis and hurricanes if they aren't built high enough.