Irregular wave runup statistics on plane beaches: application of a Boussinesq-type model incorporating a generating-absorbing sponge layer and second order wave generation

Alistair Borthwick, Colm Fitzgerald, Paul Taylor, Jana Orszaghova, Colin Whittaker, Alison Raby

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Efficient absorption of reflected waves at the offshore boundary is a prerequisite for the accurate physical or theoretical modelling of long-duration irregular wave runup statistics concerning uniform, gently sloped beaches. This paper presents a method to achieve reflected wave absorption, leading to simultaneous generation and propagation of incident waves encompassing bound wave
structure correct to second order. A generating-absorbing layer is incorporated within an existing 1DH hybrid Boussinesq-nonlinear shallow water equation model such that inshore-travelling incident waves propagate unhindered while offshore-travelling reflected waves are absorbed. During irregular wave runup simulation, a known incident wave field is imposed on the generating-absorbing sponge layer offshore of the beach. As incident waves propagate inshore, reflected wave components damp to zero across the sponge layer. At each time step, the known incident wave field is computed separately from a corresponding incident wave simulation (run in parallel with the runup simulation). Once validated, the method is used to compile random wave runup statistics on three different beach slopes broadly representative of dissipative, intermediate, and reflective beaches. Analysis of the individual runup time series, ensemble statistics and comparison to an empirical formula based on experimental runup data suggests that the main aspects of runup measured/observed in the field are properly represented by the model. The effect of the swash motions preceding one particular extreme runup event on the eventual maximum runup elevation is also investigated.
Original languageEnglish
Pages (from-to)309–324
JournalCoastal Engineering
Volume114
Early online date11 May 2016
DOIs
Publication statusPublished - Aug 2016

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