Abstract
AbstractEmbayed 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.
Highlights
Embayed beaches separated by irregular rocky headlands represent around 50% of the world’s shoreline and are important zones ecologically and commercially (Short & Masselink, 1999)
Bypassing rates are predictable for idealised headland morphologies; it remains to test the predictability for realistic morphologies, and to quantify the influence of variable morphology, sediment availability, tides and waves-tide interactions
This paper aims to test the applicability of existing headland bypassing parameterisations against realistic headland morphologies, and to expand the parameterisations to include the influence of headland underwater expression, sediment availability and embayment morphology
Summary
Embayed beaches separated by irregular rocky headlands represent around 50% of the world’s shoreline and are important zones ecologically and commercially (Short & Masselink, 1999). It has been recognised that the traditional view of embayed beaches as closed littoral cells is not accurate for many embayments, where sediment can enter and exit the system via headland bypassing (Goodwin et al, 2013; Ribeiro, 2017; Duarte et al, 2014; Valiente et al, 2019a, b; Vieira da Silva et al, 2016, 2018). Recent modelling works demonstrate bypassing rates are predictable for individual headlands (McCarroll et al, 2018; Valiente et al, 2020) and idealised headland morphologies (George et al, 2019; McCarroll et al, 2021), 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 on sand bypassing rates
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