Coastal Erosion

Hardening a shoreline can interfere with necessary profile adjustments because the dune can no

longer share its sand with the beach. As a retreating beach encounters a seawall or revetment it can

no longer draw upon a land-ward sand supply and it begins to erode.

Beach erosion leads to narrowing and, soon, beach loss. Much of Hawaii's beach loss could have been

avoided if houses were not built so close to the water. The law presently allows homes 40 feet from

the shoreline. On coasts experiencing chronic erosion this is too close and leads to hardening in order

to protect houses from the waves.

Beaches are threatened any time supply of available sand is reduced. In addition to shoreline

hardening, other processes contribute to erosion: sea-level rise, sand mining, channel dredging,

dune grading, reef degradation, and others.

Resources www.SOEST.Hawaii.Edu

Fletcher, C.H., Mullane, R.A., and Richmond, B.M., 1998. Beach loss along armoured shorelines on Oahu, Hawaiian Islands. Journal of Coastal Research, v.13, no. 1, pp. 209-215.

U.S. ARMY CORPS OF ENGINEERS, 1991. Beach response to the presence of a seawall: Comparison of field observations. U.S. Army Corps of Engineers, Coastal Engineering Research Center, Technical Report CERC-91-1, 63 pp.

Watson, S., 1997. Economic of beach restoration. Coastal Currents, Florida Coastal Management Program Newsletter, v. 5, no. 3, pp. 6-8.

BEACH FACT Seawalls

may stop coastal

erosion, but on

chronically eroding

shores, hardening leads

to beach erosion.

Coastal Erosion

Kahala Beach loss because of the shoreline armoring.

Coastal Erosion

Coastal Erosion

Coastal Erosion

Photograph taken at extreme low tide. In this erosion prone area, beach has eroded exposing rocks. The beach is much narrower because of the loss of sand. The seawalls are exacerbating the attrition and proving the information provided by SOEST as being correct.