An analysis of an attempt to control beach erosion in Chesapeake Bay, at Scientists Cliffs, Calvert County, Maryland

Abstract

An analysis was made of the functioning of 45 groins constructed to control beach erosion at Scientists Cliffs, Calvert County, Maryland. The results show that the height of groins, non-spillover length of groins, and availability of coarse sand are critical factors affecting height of sand accumulation and width of beach between groins. Very fine sand particles, smaller than 0.125 mm in diameter, are transported by wave action seaward and form very little of the sand accumulation between groins.

All relationships are illustrated graphically and with photographs. The measurements obtained were run through automatic data processing equipment to obtain regression equations and the coefficients of correlation, all of which are statistically significant.

An illustration shows the western shoreline of Chesapeake Bay for northern Calvert County in 1847 as compared with that for 1942. In a few places, the shore line has receded as much as 450 feet, whereas in other limited areas little or no erosion has occurred.

The vertical clay cliffs and bulkheads built parallel to and close to the cliffs, when not protected with groins and a sloping beach, create conditions that increase the rate of erosion and prohibit the accumulation of beach materials. Strong wave fronts that strike these vertical walls head-on at high tidal levels during storms are reflected and set up strong reflected waves that transport beach sand seaward, which exposes the hard clay cliff to further erosion.

In a fully developed or mature groin system the groins, in addition to being sand tight, should have sufficient height for at least 3/5 of their length to stop water from spillingover during most storms; and sufficient length to hold a beach wide enough so that waves do not destroy vegetation growing at the base of the cliff. However, without an adequate supply of coarse to medium sized sand particles, groins do not accumulate enough sand to control cliff erosion.