More Details on Coastal Erosion
Coastal erosion is a hazard to humans who build structures within reach of erosional processes.
Willard Bascom portrayed this natural process as a struggle between the sea (attacking the land relentlessly, in disguise, by collecting the energy of wind and transporting it to shore) and the land (defending itself with subtle skill, using beach and bluff materials).
Reference: Willard Bascom. 1980. Waves and Beaches. Prologue. Anchor Press/Doubleday. New York.
Erosion comes in different forms. There is the unnoticed daily loss of grains of soil from rain falling directly on bare slopes or runoff from rain, snow melt and groundwater seepage running down the faces of bare slopes. Over years, these losses can result in major retreat, called recession. Erosion can also come in sudden small or large slumps of bluff top material. A few feet to tens of feet from the bluff edge, a crack appears. The bluff edge land drops a few inches, a few feet, or slides thundering down the slope to the beach below.
The area of the coast within which erosion is a hazard for structures within their useful lifetimes is sometimes called an Erosion Hazard Area or Erosion Hazard Zone. The width of this area, measured roughly perpendicular to shore, is determined by multiplying an erosion rate times a period of time.
It is a challenging task to adequately estimate for a particular construction site the future recession rate for that site, and the expected life of the structure to be built on the site. The estimate made by multiplying these two terms is tailor-made for the structure and is called a Construction Setback (or a Setback, for short). The clock is running on use of many Construction Setback estimates. The estimate is made from the edge of a bluff or bank slope that may be constantly, or periodically moving landward.
Erosion of dunes and beaches may be reversible as wind and waves build or remove their materials. Erosion of bluffs and banks is by nature irreversible.
Related to coastal erosion are coastal bluff failures and lakebed erosion. Both are described in detail under separate headings in the Coastal Hazards section.