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 idealised 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 modelled bypassing rates are quantified for 29 headlands
under variable wave, tide and sediment conditions along 75km 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 modelled 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 4.4. This work demonstrates wave-dominated headland bypassing is
amenable to parameterisation and highlights the extent to which headland
bypassing occurs with implications for embayed coasts worldwide.