Berm formation and dynamics on a gently sloping beach; the effect of water level and swash overtopping (original) (raw)

Earth Surface Processes and Landforms, 2009

Abstract

ABSTRACT Berm formation and morphological development of the beach face have been observed during a neap-neap tidal cycle on the gently sloping and accreting beach at Vejers, Denmark. During the field campaign, an intertidal bar migrated onshore and stabilized as a berm on the foreshore. A new intertidal bar occurred on the lower beach face, migrated onshore on the rising tide and finally merged with the pre-existing berm. As the tide continued to rise, the new berm translated further onshore as an intertidal bar to the uppermost part of the foreshore. The sediment transport during the berm transition was onshore directed in the upper swash and offshore directed in the lower swash. This berm development can be described through both the neap-berm, ridge-and-runnel and berm-ridge development concepts proposed by Hine (Sedimentology 1979; 26: 333-351), and all three stages were observed during only three tidal cycles. The main factors controlling this fast transformation were the gentle slope of the cross-shore profile, rapid water level translation rates, substantial swash overtopping of the berm, and low infiltration rates. Despite the onshore migration of intertidal bars and berm formation, no net foreshore accretion took place during the field campaign. This was largely due to the formation of rip channels with strong rip currents cutting through the intertidal bars and the berm, which acted as a sediment drain in the profile.

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