Abstract
Our ability to predict beach erosion above the still water level (SWL) is still not satisfactory due to the lack of adequate technology to accurately measure the sediment concentration and velocity in very shallow water, including the swash zone where the beach face is intermittently covered with water and exposed to the atmosphere. A simple procedure is proposed here to improve our predictive capability for the particular case of scarping erosion caused by wind-generated waves above the SWL. If the slope at the steep scarp is larger than the limiting slope of the internal sediment friction, the steep face is assumed to be eroded due to the computed offshore sediment transport at the toe of the scarp. The bedload and suspended sediment transport at the toe of the scarp was computed using a time-averaged model that includes the steep bottom slope effect. The model was validated against a novel experiment in a multidirectional wave basin, where scarping was reproduced. The water level was raised in four steps to reproduce the shoreface erosion, berm overwash and berm erosion, successively. Horizontal and tilted berms were tested against similar normal incident irregular waves to compare the performance of the profile without and with ponding, respectively. For the tilted case, ponding appeared when the tilted berm was overtopped. No ponding was observed for the horizontal berm test even when the berm was overtopped. The predictability was estimated using the Brier skill score (BSS). The predictability of the scarping was good (BSS ≥ 0.6) for the horizontal berm test and fair (BSS ≥ 0.4) for the tilted berm test. This decrease in the predictability may be related to the ponding, which is not included in the model.
Highlights
IntroducciónIn Europe, an estimated average of 5400 million euros are used per year to mitigate coastal erosion and protect dwellings, resorts, infrastructure and other real estate along the coastlineSe estima que en Europa se invierten un promedio de 5400 millones de euros anuales para paliar los efectos de la erosión costera y proteger zonas residenciales, complejos turísticos, Ciencias Marinas, Vol 34, No 1, 2008(www.eurosion.org)
We address the problem of predicting the erosion rate above the still water level (SWL) on an alongshore uniform beach consisting of well-sorted sand under the attack of irregular normally incident short waves
The water level was raised in four steps to successively reproduce the foreshore erosion, and the berm overwash, erosion and destruction
Summary
In Europe, an estimated average of 5400 million euros are used per year to mitigate coastal erosion and protect dwellings, resorts, infrastructure and other real estate along the coastline. Van Rijn et al (2003) mostraron cómo algunos modelos de variación del perfil de playa, después de ser calibrados, podían reproducir los movimientos de la barra de arena en la escala de tormentas, no obstante la predicción de las variaciones del perfil por encima del nivel medio del mar en reposo (en adelante referido por sus siglas en inglés, SWL) todavía se encuentra en una etapa temprana de desarrollo. En este trabajo se analizan los mecanismos de erosión por escarpe por encima del SWL. En este estudio se aborda el problema de la estimación de la tasa de erosión por encima del SWL en una playa inicialmente uniforme, de arena bien seleccionada, bajo la acción de oleaje irregular de periodo y de incidencia predominantemente normal a la playa.
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