Coastal geomorphology, is the study of the morphological development and evolution of the coast as it acts under the influence of winds, waves, currents, and sea-level changes. This study of physical processes and responses in the coastal zone is often applied in nature, but it also involves basic research to provide the fundamental understanding necessary to address the pertinent questions. A principal coastal concern today and in the foreseeable future is beach erosion. It is estimated that 70 % of the world's sandy shorelines are eroding. In the United States the percentage may approach 90 %.