This study documents the development of a beach berm and the associated closure of an intermittently open coastal lagoon on a gently sloping beach on the east coast of Australia. The berm grew 1.17 m in elevation over 11 days, and essentially closed the lagoon except at high tide within 4 days after opening. Berm growth was vertical with no notable horizontal accretion in the shore normal direction. Wave runup and overtopping were also measured and overtopping into the lagoon channel was found to be dominated by long waves. Berm development is found to be largely dependant upon swash and overtopping potential. Large overtopping potential at the start of the experiment resulted in substantial sediment transport, deposition and rapid berm growth. With berm growth, overtopping potential ultimately become restricted, reducing the sediment volumes deposited and consequently limiting further berm growth.
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