<p>Embayed beaches separated by irregular rocky headlands represent around 50% of the world&#8217;s shoreline and are important zones ecologically and commercially. Accurate determination of sediment budgets is necessary for prediction of coastal change over long timescales in these zones. Some headlands have been shown to permit sediment bypassing under particular forcing conditions, therefore knowledge of sediment inputs and outflows via headland bypassing are important for sediment budget closure. Recent modelling work demonstrates bypassing rates are predictable for an isolated headland, however, it remains to test this predictability using a range of real headland morphologies, and to examine the influence of embayment morphology, sediment availability and tidal effects.</p><p>We show that bypassing rates are strongly influenced by the relative proximity between adjacent headlands, and the degree of embaymentisation. Tidal currents are secondary to wave forcing, mildly moderating bypass rates, whereas tidal elevation strongly influences bypassing rates largely through variations in apparent headland and embayment morphology.</p><p>A fully coupled (3D hydrodynamics and waves) numerical model was used to simulate sand transport along a 75 km long macrotidal, embayed coast in the north of Cornwall, UK. Twenty-five embayments were included in the analysis. Nine wave conditions were simulated and bypass rates were analysed for three tidal elevations. Simulations were performed with both uniform sediment availability and a realistic spatial distribution of sediment, and both including and excluding tidal currents. It is shown that many of the embayments along this stretch of coast exhibit headland bypassing under energetic wave forcing, highlighting the need for accurate bypass rate predictions for sediment budget determination on embayed coasts.</p><p>Headland extent relative to surf-zone width was a critical control on sand bypass rates in line with previous work. Predictive expressions were accurate to within a factor of 4 for beaches exhibiting a &#8216;normal&#8217; circulation pattern (embayment length long relative to surf zone width), however, they did not predict well cases where embayment cellular circulation was dominant (embayment length short relative to surf zone width). &#160;Tidal currents exhibited a secondary control relative to wave forcing, moderating bypass rates by up to 20% in this macrotidal environment. Large differences in the apparent morphology of the embayments between high and low tide strongly impact bypassing rates, with greatest bypassing occurring at low-tide when headland cross-shore length is smallest. Bypass rates were reduced for realistic sediment distributions versus uniform sediment availability, due to larger transport magnitudes when sediment is available off the headland toe.</p><p>This work highlights the extent to which headland bypassing occurs along this embayed coast with implications for similar coasts worldwide. It also emphasises the need for accurate predictions of headland bypassing in these regions and suggests areas for further efforts to focus to refine future predictive parameterisations.</p>
Mouth bars are morphological units important for deltas, estuaries, or rivers debouching into the sea. Several processes affect the formation of these deposits. This paper focuses on the role of tides on shaping mouth bars, presenting both hydrodynamic and morphodynamic results. The effect of tides is analyzed in two end‐member configurations: a river with a small tidal discharge compared to the fluvial discharge (fluvial dominated) and a river with a very large tidal discharge (tidal dominated). Mouth bar formation is analyzed using the coupled hydrodynamic and morphodynamic model Delft3D. The presence of tides influences the hydrodynamics of the jet exiting the river mouth and causes an increase in the averaged jet spreading. At low tide the lower water depth in the basin promotes a drawdown water profile in the river and an accelerated flow near the mouth. The resulting velocity field is characterized by residual currents affecting growth and final shape of the mouth bar. Simulations indicate that mouth deposits are characterized by the presence of two channels for negligible tidal discharge, whereas three principal channels are present in the tidal‐dominated case, with a central channel typical of tidal inlets. On the basis of our numerical analyses, we present a robust criterion for the occurrence of mouth deposits with three channels. Trifurcations form when the tidal discharge is large with respect to the fluvial one and the tidal amplitude is small compared to the water depth. Finally, predicted mouth bar morphologies are compared with good agreement to river mouths in the Gulf of Mexico, USA.
Abstract Embayed beaches separated by irregular rocky headlands represent 50% of global shorelines. Quantification of inputs and outflows via headland bypassing is necessary for evaluating long‐term coastal change. Bypassing rates are predictable for idealized headland morphologies; however, it remains to test the predictability for realistic morphologies, and to quantify the influence of variable morphology, sediment availability, tides and waves‐tide interactions. Here we show that headland bypassing rates can be predicted for wave‐dominated conditions, and depend upon headland cross‐shore length normalised by surf zone width, headland toe depth and spatial sediment coverage. Numerically modeled bypassing rates are quantified for 29 headlands under variable wave, tide and sediment conditions along 75 km of macrotidal, embayed coast. Bypassing is predominantly wave‐driven and nearly ubiquitous under energetic waves. Tidal elevations modulate bypassing rates, with greatest impact at lower wave energies. Tidal currents mainly influence bypassing through wave‐current interactions, which can dominate bypassing in median wave conditions. Limited sand availability off the headland apex can reduce bypassing by an order of magnitude. Bypassing rates are minimal when cross‐shore length >5 surf zone widths. Headland toe depth is an important secondary control, moderating wave impacts off the headland apex. Parameterisations were tested against modeled bypassing rates, and new terms are proposed to include headland toe depth and sand coverage. Wave‐forced bypassing rates are predicted with mean absolute error of a factor 4.6. This work demonstrates wave‐dominated headland bypassing is amenable to parameterization and highlights the extent to which headland bypassing occurs with implications for embayed coasts worldwide.
Coastal protection is of paramount importance because erosion and flooding affect millions of people living along the coast and can largely influence countries’ economy. The implementation of nature-based solutions for coastal protection, such as sand engines, has become more popular due to these interventions’ adaptability to climate change. This study explores synergies between AI and hydro-morphodynamic models for the creation of efficient decision-making tools for the choice of optimal sand engines configurations. Specifically, we investigate the use of long-short-term memory (LSTM) models as predictive tools for the morphological evolution of sand engines. We developed different LSTM models to predict time series of bathymetric changes across the sand engine as well as the time-decline in the sand engine volume as a function of external forces and intervention size. Finally, a MATLAB framework was developed to return LSTM model results based on users’ inputs about sand engine size and external forcings.
Earth and Space Science Open Archive This preprint has been submitted to and is under consideration at Journal of Geophysical Research - Oceans. ESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary.Learn more about preprints preprintOpen AccessYou are viewing the latest version by default [v1]Wave, Tide and Topographical Controls on Headland Sand BypassingAuthorsErin VictoriaKingiDDaniel CConleyiDGerhardMasselinkNicolettaLeonardiRobert JakMcCarrollTimothyScottiDNievesGarcia ValienteiDSee all authors Erin Victoria KingiDCorresponding Author• Submitting AuthorUniversity of PlymouthiDhttps://orcid.org/0000-0002-9641-1239view email addressThe email was not providedcopy email addressDaniel C ConleyiDUniversity of PlymouthiDhttps://orcid.org/0000-0001-6822-5386view email addressThe email was not providedcopy email addressGerhard MasselinkPlymouth Universityview email addressThe email was not providedcopy email addressNicoletta LeonardiUniversity of Liverpoolview email addressThe email was not providedcopy email addressRobert Jak McCarrollPlymouth Universityview email addressThe email was not providedcopy email addressTimothy ScottiDUniversity of PlymouthiDhttps://orcid.org/0000-0002-3357-7485view email addressThe email was not providedcopy email addressNieves Garcia ValienteiDMet OfficeiDhttps://orcid.org/0000-0003-1716-0767view email addressThe email was not providedcopy email address
Abstract We use field data and a cellular automata model to investigate salt marsh response to wave action under different wave energy conditions and frequency of extreme events. Our results suggest that salt marsh response to wind waves is tied to their local properties. In case of low‐wave‐energy conditions, local variability in marsh resistance might lead to the unpredictable failure of large marsh portions with respect to average erosion rates. High‐wave‐energy conditions, while overall leading to faster marsh deterioration, produce constant and predictable erosion rates. A high occurrence of extreme events leads to smoother and more uniformly deteriorating marsh boundary profiles. Salt marshes subject to weak wave energy conditions are the most susceptible to variations in the frequency of extreme events. This suggests that variations in time in the morphology of salt marsh boundaries could be used to infer changes in frequency and magnitude of external agents.
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