potentially excellent recreational site. The sill can be constructed of various materials, but it must be
impermeable to the passage of the retained beach sand by using, for instance, a filter cloth behind and
beneath the structure. The cloth prevents the fill from escaping through any large voids in the sill and
also stabilizes the structure against settlement. While a graded stone core could also be used in a rock
sill in place of filter cloth, the limited height of such sills generally precludes use of muli-layered
structures of this kind. The figure also shows a splash apron which is provided to prevent scour and
erosion of the beach fill from overtopping waves.
Perched beaches can be provided where offshore slopes are mild enough to permit the use of a sill
in shallow water at a reasonable distance from shore.
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