Beach and lake shore erosion is a serious problem. Sea walls of various types can prevent the damage done by seasonal variations in water level, flooding and tidal erosion. Shore conditions help determine the type of seawall construction and materials used. Mortared stone, stone block and steel-reinforced concrete are all used in constructing seawalls. These materials work well to reduce erosion but allow water, from flooding or high tides, to build up behind the wall. For inland applications rock riprap, combined with shore plants, is the preferred method of erosion abatement.
Riprap is stone of various types that is used to protect, or armour, a shoreline or river bank. Riprap is often a mixture of granite, limestone and concrete rubble in chunks spread along the shore. This form of revetment is often used because it allows plant life to grow in the surrounding soil and in the crevices between the stones. Riprap seawalls are effective because they dissipate the force of waves before it can reach the soil and sand behind the rocks. Riprap is also used to reinforce old seawalls by placing it at the bottom of the walls.
Cobble boulder seawalls are a familiar sight along lake shore beaches and river banks. Large, round cobbles held together with mortar angle down towards the water. Cobble boulder seawalls are usually placed in less demanding areas where wave action is not extreme. This type of revetment is composed of large rocks stacked over a mound of rubble, small stones and dirt. The stones can be piled in place with open spaces to allow water to flow through or joined with mortar.
Concrete seawalls reinforced with steel are large structures designed to protect coastal areas from heavy wave action. Coastal cities invest large sums of capital into seawall building and maintenance. This type of concrete erosion barrier is often built using large concrete sections which are lowered into place with a crane. Concrete seawalls are made with different face shapes and are held in place with heavy pilings. Curved seawall faces break up the wave energy and direct it back outwards while straight-faced seawalls absorb the impact.
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