Morphological evolution of a submerged artificial nearshore berm along a low-wave microtidal coast, Fort Myers Beach, west-central Florida, USA

Abstract

Nourishment in the nearshore is becoming an increasingly utilized method for regional sediment management, particularly for dredged material that contains more fine sediment than the native beach. A nearshore berm was constructed at Fort Myers Beach, Florida, USA using mixed-sized sediment dredged from a nearby channel. The nearshore berm, which is the shallowest of its kind, was placed in water depths between 1.2 and 2.4m with the berm crest just below the mean lower low water level. Based on time-series profiles surveyed from 2009 to 2013, the nearshore berm migrated onshore while the system was approaching a dynamic equilibrium. The distant passage of two tropical storms in the third year generated exceptionally high waves for the study area. Substantial profile change induced by the energetic conditions contributed to rapid evolution of the berm profiles toward equilibrium. Near the end of the fourth year, the berm profiles had returned to the equilibrium shape characteristic of the study area. Gaps in the berm allowed water circulation when the berm became emergent and watercraft access to the beach for recreational purposes. Gaps should be considered as a design parameter for future berm nourishments. Sediment samples collected and analyzed showed that the fine sediment content in the original placed material was selectively transported and deposited offshore, while the coarser component moved onshore. The dry beach maintained the same sediment properties throughout the study period and was not influenced by the fine sediment in the initial construction of the berm.