Empirical modelling of beach evolution: implementation of coupled cross-shore and longshore approaches

Teddy Chataigner,Nicolas Le Dantec,Marissa Yates

doi:10.5194/egusphere-egu2020-17932

Abstract

&lt;p&gt;Understanding shoreline evolution, and in particular, the consequences of shoreline erosion is a&lt;br&gt;major societal concern that threatens to become even more important in the future with the impacts&lt;br&gt;of climate change. Thus, it is necessary to improve both knowledge of the dominant physical processes&lt;br&gt;controlling medium to long-term shoreline evolution and the capabilities of morphological evolution&lt;br&gt;models to simulate beach changes at these spatial and temporal scales.&lt;br&gt;Empirical models may be an ideal choice for modelling complex and dynamic environments such as&lt;br&gt;sandy beaches at large spatial (beach) and long temporal (years to decades) scales. They reproduce&lt;br&gt;the effects of the main morphodynamical processes with low computational cost and relatively high&lt;br&gt;accuracy, in particular when high quality, long-term data are available for calibration.&lt;br&gt;Here, to broaden its range of application, a cross-shore equilibrium model, which has demon-&lt;br&gt;strated its accuracy and efficiency in reproducing shoreline and intertidal beach profile changes at&lt;br&gt;several micro and macrotidal beaches, is extended to couple it with a longshore beach evolution&lt;br&gt;modelling approach. The selection of a particular longshore model (based on a one-line approach),&lt;br&gt;and its implementation and validation with benchmark test cases of shoreline evolution caused by&lt;br&gt;the effects of diffusion, high angle wave instabilities, and coastal structures are presented.&lt;br&gt;The new hybrid model is applied at Narrabeen beach to reproduce the long-term evolution of&lt;br&gt;beach contours near the shoreline. The model is calibrated and tested using the 40-year timeseries of&lt;br&gt;monthly subaerial beach profile surveys conducted along 5 cross-shore profiles along the 3.6km-long&lt;br&gt;Narrabeen-Collaroy embayment. The novelty of the current work is to focus on reproducing changes&lt;br&gt;at different altitudes, with the objective of assessing the cross-shore variability of the longshore&lt;br&gt;sediment flux, which is assumed constant in most one-line longshore transport models. The coupled&lt;br&gt;model performance is discussed, and the results are compared to existing studies that have simulated&lt;br&gt;shoreline evolution at Narrabeen using other morphological change models.&lt;/p&gt;

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