Beach face and berm morphodynamics fronting a coastal lagoon

Weir, F. M., Hughes, M. G. and Baldock, T. E. (2006) Beach face and berm morphodynamics fronting a coastal lagoon. Geomorphology, 82 3-4: 331-346. doi:10.1016/j.geomorph.2006.05.015

Author Weir, F. M.
Hughes, M. G.
Baldock, T. E.
Title Beach face and berm morphodynamics fronting a coastal lagoon
Journal name Geomorphology   Check publisher's open access policy
ISSN 0169-555X
Publication date 2006
Sub-type Article (original research)
DOI 10.1016/j.geomorph.2006.05.015
Volume 82
Issue 3-4
Start page 331
End page 346
Total pages 16
Editor A. M. Harvey
R. A. Marston
Place of publication Netherlands
Publisher Elsevier BV
Collection year 2006
Language eng
Subject C1
290899 Civil Engineering not elsewhere classified
770400 Coastal and Estuarine Environment
09 Engineering
0911 Maritime Engineering
Abstract This study documents two different modes of berm development: (I) vertical growth at spring tides or following significant beach cut due to substantial swash overtopping, and (2) horizontal progradation at neap tides through the formation of a proto-berm located lower and further seaward of the principal berm. Concurrent high-frequency measurements of bed elevation and the associated wave runup distribution reveal the details of each of these berm growth modes. In mode I sediment is eroded from the inner surf and lower swash zone where swash interactions are prevalent. The net transport of this sediment is landward only, resulting in accretion onto the upper beach face and over the berm crest. The final outcome is a steepening of the beach face gradient, a change in the profile shape towards concave and rapid vertical and horizontal growth of the berm. In mode 2 sediment is eroded from the lower two-thirds of the active swash zone during the rising tide and is transported both landward and seaward. On the falling tide sediment is eroded from the inner surf and transported landward to backfill the zone eroded on the rising tide. The net result is relatively slow steepening of the beach face, a change of the profile shape towards convex, and horizontal progradation through the formation of a neap berm. The primary factor determining which mode of berm growth occurs is the presence or absence of swash overtopping at the time of sediment accumulation on the beach face. This depends on the current phase of the spring-neap tide cycle, the wave runup height (and indirectly offshore wave conditions) and the height of the pre-existing berm. A conceptual model for berm morphodynamics is presented, based on sediment transport shape functions measured during the two modes of berm growth. (c) 2006 Elsevier B.V. All rights reserved.
Keyword Geography
Berm development
Beach erosion
Progradation and prograding coasts
Concurrent measurements
Swash zone
Berm Crest
Beach face gradient
Q-Index Code C1

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Created: Wed, 15 Aug 2007, 10:38:21 EST