Numerical modeling of shoreline undulations part 2: Varying wave climate and comparison with observations

Abstract

a b s t r a c t a r t i c l e i n f oThe present work applies the shoreline model from part 1 to a real environment. In part 1, a numerical shoreline model which could handle the development of arbitrarily shaped shorelines was applied to consider the development of shoreline undulations on an unstable shoreline exposed to incoming waves with a directional spreading. In this paper, these findings are extended to firstly include the effect of a varying wave climate on the shoreline morphology and secondly, to tune the model to two naturally occurring shorelines. It is found that the effect of a variable wave climate is to slow down the development of the morphology and in some cases to inhibit the formation of shore-parallel spits at the crest of the undulations. On one of the natural shorelines, the west coast of Namibia, the shore is exposed to very obliquely waves from one main direction. Here, the shoreline model is able to describe the observed shoreline features qualitatively and quantitatively. The model slightly over-predicts the scale of the feature and, associated with this, slightly under-predicts the migration speeds of the features. On the second shoreline, the west coast of Denmark, the shore is exposed to waves with an angle close to the critical around 45°, and here the existence of undulations is discussed in detail.

Predicting Climate‐Driven Coastlines With a Simple and Efficient Multiscale Model

“…Although they are the most representative of morphological processes, they are limited by the extent and frequency of available historical data. Process‐driven models characterize the dominant physical processes shaping coastlines such as gradients in longshore sediment transport (LST) (Ashton et al, , ; Ashton & Murray, , ; Arriaga et al, ; Falqués et al, ; Hanson, ; Idier et al, ; Kaergaard & Fredsoe, , ; Murray & Ashton, ), wave‐driven cross‐shore shoreline change (Yates et al, , ; Davidson et al, , ; Splinter et al, , ), beach profile response to water levels and waves (Aagaard, ; Kriebel & Dean, ; Miller & Dean, ; Larson et al, ; Patterson & Nielsen, ), and profile adjustment due to SLR (Bruun, ) without solving complex governing equations as physics‐driven models do. Process‐driven models have been proven reliable and computational inexpensive; however, they usually focus on solving a single physical process.…”

Self‐organized kilometer‐scale shoreline sand wave generation: Sensitivity to model and physical parameters

“…For instance, after Ashton and Murray [], an increase of wave height H and period T leads to an increase of the diffusional time scale ( ), i.e., speeds up the sand waves development in case of high‐angle waves. Kaergaard and Fredsoe [, ] investigated the effect of wave directional spreading, the closure depth D c , and the shoreface steepness and showed that sand wave wavelength increases with increasing directional spreading and D c , while it decreases with increasing shoreface steepness. However, these studies did not investigate the effect of these parameters on the instability onset.…”

How kilometric sandy shoreline undulations correlate with wave and morphology characteristics: preliminary analysis on the Atlantic coast of Africa

“…Third, the Atlantic coast of Africa is exposed to larger wave height and period than the ones used in the model analysis. Forth, as suggested by Kaergaard and Fredsoe (2013b), the smallest waves within the wave spectrum arrive with a larger obliquity at the coast and can contribute to the shoreline instability even more than the dominant waves. Finally, the sensitivity of the ratio results should be analysed taking into account the data quality.…”

“…The mean wave approach is quite oblique there, from the NW, but the angle with the shore normal is nearly at the threshold of instability. Kaergaard and Fredsoe (2013b) have done the corresponding stability analysis and concluded that only if the large storm waves were excluded from the wave climate the coastline would be unstable and shoreline sandwaves with the observed wavelength would emerge. Kaergaard et al (2012) investigated also the cross-shore extent of coastline undulations on a site located on the West coast of Denmark, based on specific bathymetric surveys providing temporal and spatial data.…”

“…That coast appeared to be at the threshold for instability and can be stable/unstable depending of some of the hypothesis of the study. Kaergaard and Fredsoe (2013b) investigated possible HAWI occurrence on the West coast of Denmark. The mean wave approach is quite oblique there, from the NW, but the angle with the shore normal is nearly at the threshold of instability.…”