When you build a sandcastle on the beach, you don't expect it to last forever. You spread out your towel to sunbathe, but you know you can't stay in the same spot all day without getting wet. Venturing into the ocean to swim, you are cautious - wondering what the currents are doing that day. Subconsciously, you are attuned to the fact that the coastal environment is constantly changing.
Coastal erosion is a natural process even in pristine environments.
However, in areas where human activity negatively impacts the shoreline, coastal erosion can become a serious problem. Beach sand originates mainly from rivers and streams which carry it directly to the ocean. Sand also comes from the gradual weathering of exposed rock formations and cliffs along the shore, and from the deterioration of shell, coral, and other skeletal fragments. Wave action, wind, and currents move sand up and down the coast. This movement is called longshore transport.