Depth of Closure

If the depths offshore of a beach are measured repeatedly, there appears to be an offshore depth beyond which the depths do not change with time. This is the depth of closure and it is obviously deeper then that portion of the beach profile that changes seasonally or due to storms. It is on the order of 7 m on the East Coast of the U.S.

Hallermeier (1978; 16th Int. Conf. Coastal Eng.) gave an expression for the depth of closure in terms of the wave height and period, and the sediment density. This expression can be written for a single wave train in terms of deep water values of the wave height as well. This applet gives two choices for this expression.

Hallermeier also gave an expression for the depth of closure for the "effective" wave height, H_e , which is that wave height that is only exceeded 12 hours per year. It can be related to the mean wave height and its standard deviation.

Birkemeier (1985, J.WPCOE), using Duck, NC field data, showed a different relationship in terms of H_e . This applet allows the use of any one of these four methods to determine the depth of closure; thru the use of the choice button. The two methods using the effective wave height are given simultaneously: Hallermeier's method is denoted as d_H and Birkemeier's as d_B.

Comments: Robert A. Dalrymple
Center for Applied Coastal Research
University of Delaware, Newark DE 19716