Beach Change Magnitudes in Relation to Dynamic Phases on Dissipative Coastsby Effiom Edem Antia, Univ of Calabar, Calabar, Nigeria,
Abstract: Dissipative-prone beaches are statistically and aethestically the most significant on open sea sandy coasts. These beaches owe their widespread occurrence to their temporal stability. They are typically fine-grained with wide, low gradient foreshore and surfzone regions commonly subjected to moderate-high wave conditions. In general, knowledge of the temporal and spatial scale (expressed linearly or volumetrically) and sense (erosion or accretion) of beach change is an inevitable step towards a coherent coastal management. Equally important to the latter is the ability to intercompare information on temporal dynamics from similar beaches. Unfortunately, inconsistencies in the often reported magnitudes prohibit any such attempt. This study was specifically undertaken to evaluate interrelationships between magnitudes of linear (m) and volumetric (m3/m) change of dissipative beaches during dynamic phases of accretion and erosion respectively. The study area is situated on the southeastern Atlantic coast of Nigeria. A total of 166 pairs of linear and volumetric beach change data were obtained during a 19-month field monitoring programme, spanning a wide range of wave conditions. Present results show that the sense of linear and volumetric beach change on dissipative coasts is not consistently compatible. Beaches may therefore accrete linearly with a corresponding loss in sediment volume over a comparable time-interval, and vice-versa. However, at instances where both scales of change show a similar tendency, magnitudes of volumetric accretion and erosion can be estimated from their easily measured linear counterparts, by respectively dividing the latter estimates with beach factor values of 1.4 and 2.2 m/m2.
Subject Headings: Beaches | Linear functions | Beach accretion | Erosion | Sediment | Coastal management | Developing countries | Nigeria | Africa
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