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Volume 15, Issue 1 - March 2015

 

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  • Abstract / Resumo
  • References / Bibliografia
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Revista de Gestão Costeira Integrada
Volume 15, Número 1, Março 2015, Páginas 21-33

DOI: 10.5894/rgci530
* Submission: 25 JUN 2014; Peer review: 19 AUG 2014; Revised: 2 MAR 2015; Accepted: 3 MAR 2015; Available on-line: 5 MAR 2015


Model of the evolution of mounds placed in the nearshore *  

Magnus Larson@, a; Hans Hansona


@ - Corresponding author, to whom correspondence should be addressed.
a - Lund University, Department of Water Resources Engineering, Box 118, S-221 00 Lund, Sweden. E-mails: Larson [email protected]; Hanson <[email protected]>   


ABSTRACT
A one-dimensional mathematical model is presented that describes the cross-shore evolution of a long linear mound of noncohesive sediment placed in the nearshore and exposed to non-breaking waves. The equation for the transport rate accounts for wave asymmetry and gravity, and the net rate is expressed by reference to an equilibrium profile shape. Simplifications reduce the governing equation for mound evolution to the diffusion equation, for which analytical solutions are available for various initial shapes of the mound. Temporal and spatial dependencies governing mound evolution are obtained from the analytic solutions; for example, a doubling of the wave height implies a certain mound response in 1/8 of the time compared to the original conditions. The governing equation is also solved numerically in order to avoid schematization of the forcing, initial, and boundary conditions. Both the analytical and numerical models are compared with data on mound evolution from several sites around the world. Model predictions agree with trends in measurements of four mounds at widely different sites. An example is given concerning the application of the analytical model for preliminary mound design. The formulation presented also applies to infilling of dredged trenches with lengths much greater than their widths.

Keywords: sediment transport, dredging, profile evolution, beach nourishment, mound design.   


Model of the evolution of mounds placed in the nearshore

RESUMO
A evolução morfodinâmica de um banco de areia existente na zona costeira do oceano antes da zona de rebentação é descrita recorrendo a um matemático unidimensional. As taxas de transporte sedimentar são calculadas relativamente a um perfil de equilíbrio e têm em conta a assimetria das ondas e o termo gravitacional. A equação de balanço que rege a evolução da morfologia do fundo, sob certas hipóteses, reduz-se a uma equação de difusão que tem solução analítica conhecida para diferentes condições iniciais. Para condições mais gerais, a equação é resolvida numericamente. Os resultados numéricos obtidos descrevem a tendência das observações efetuadas em quatro bancos de areia distintos. O modelo analítico desenvolvido é aplicado para estudar a configuração inicial de um banco de areia. A formulação apresentada pode também ser aplicada para estudar a evolução da morfologia de escavações resultantes de dragagens com uma configuração em que o seu comprimento é maior do que a sua largura.
   
Palavras-chave: transporte de sedimentos, dragagem, evolução de perfil, alimentação artificial, projeto de banco de areia. 

 

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