Abstract
This paper deals with a laboratory study on wave transmission at breakwaters of OCT (Oyster CASTLE-type) blocks on mangrove mudflats. The aim is to examine characteristics of wave transmission in connection with conditions favourable for mangrove rehabilitation in the Mekong River Delta. Across-structure wave energy balance and exchange of fine sediment were examined in comparison with several existing types of permeable breakwaters. It is shown that porous-type structures like the OCT breakwater are more advantageous over hollow-type ones and are generally recommended for use in favour of mangrove re-colonization.The bulk porosity is shown to play an exceptional role in controlling wave transmission as well as exchange of fine sediment. Long-period/infra-gravity waves (IG) are not effectively dissipated by the structure, which is in contrast to short-period (SS) ones. Transmission of IG waves is found to virtually depend on the bulk porosity only, but not on geometric parameters like SS waves. The result consolidates the assumption that transport of mud through the structure is largely associated with IG waves. For the functional design of OCT breakwaters, an empirical formula of wave transmission has been derived, in which the structure permeability effect expressed in terms of the bulk porosity is explicitly incorporated.
Published Version
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