An XBeach derived parametric expression for headland bypassing

Accurate knowledge of the sediment budget a coastal cell is necessary for management and predicting long-term change. An important component in many wave-dominated embayed coastlines amount that bypasses rocky headlands, which present partial barriers to alongshore transport. As yet, there no universal method estimating bypass rates. Here we show wave-forced bypassing an isolated headland can be estimated using parameterisation wave conditions, shoreface slope, size, toe-depth cross-shore extent. XBeach was used simulate instantaneous rates flux off apex idealised headland, with >1100 simulations, testing various morphological factors. Key variables were extent as ratio bed slope (XH = htoe/tanβ) surfzone function breaking depth (Xs hb/tanβ). The critical controlling found XH/XS (equivalent htoe/hb, headland). Bypass predicted as: Qbypass Q0 f(XH/XS); where Q0, transport rate immediately updrift based on existing expression (Van Rijn, 2014) f(XH/XS) negative exponential function. This formulation accurately replicated modelled by XBeach, generally within factor two. Headland shape lower-order control excluded from parameterisation. Preliminary analysis suggests may also applied groynes, though more specific required. Once adapted time-varying water levels, succesfully three observed headlands over single event. Best results obtained measured parameterise morphometry. Further field data are required robust calibration, particular large complex vary substantially model development. provide first-pass estimate wide-range types; this will use managers, scientists engineers working coastlines.