Erosion is part of a larger process known as littoral transport. Littoral transport is the movement of material by waves and currents on the coastline. The material being transported is primarily sand and gravel, with a small percentage of silt-sized particles and rocks. The source or supply of nearly all of the sand that is in the littoral transport system of the Great Lakes is from the erosion of the bluffs and dunes. Very little material is supplied by rivers.
Littoral transport occurs both along the shoreline, as well as into the lake and onto the shore.
With respect to sand supply, a given length of coastline may have a surplus, be in balance, or have a deficit in its sand supply budget. A sand supply would be in balance for a particular area if the amount of sand leaving the area was being replaced by an equal amount of sand arriving from adjoining areas. A large reduction in the sand supply, or a long term reduction in supply to an area, creates a deficit in the sand budget that must be balanced, usually by increased erosion. Sand supply influences erosion by supplying the material that builds and maintains beaches, offshore bars, and the general beach profile. These features dissipate wave energy and the absence of these features, where they would normally be present, usually results in increased erosion.