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

对于海岸管理和预测长期海岸变化，必须准确了解海岸单元的沉积物预算。在许多以波浪为主的嵌入式海岸线中，沉积物预算的重要组成部分是绕过岩石岬角的沉积物数量，这些岩石岬角构成了对沿海运输的部分障碍。迄今为止，还没有通用的方法来估算旁路速率。在这里，我们表明，可以通过使用波浪条件，岸坡，沉积物大小，岬角趾深和跨岸范围的参数化来估计孤立岬角的波浪绕过。XBeach用于模拟理想化和孤立岬角顶点附近的沿海通量的瞬时速率，并进行了1100多次模拟，测试了各种波浪和形态因素。X _H = h _toe /tanβ）和冲浪区范围作为破坏深度和斜率的函数（X _s = h _b /tanβ）。发现控制旁路的临界比为X _H / X _S（对于理想的岬角，等于h _toe / h _b）。旁路预测为：Q_旁路= Q ₀ f（X _H / X _S）；其中Q ₀是陆岬的立即向上漂移的近岸运输速率，它基于现有表达式（Van Rijn，2014）和f（X_高/ X _S）是负指数函数。该公式准确地复制了XBeach建模的旁路速率，通常在两倍之内。发现岬角形状是旁路的低阶控制，因此未包含在参数设置中。初步分析表明，该表达方式也可能适用于防波堤，尽管需要进行更具体的测试。一旦适应了随时间变化的海浪和水位，该表达式就可以成功预测一次事件中三个观测到的岬角的旁路率。使用测得的脚趾深度对岬角形态进行参数设置可获得最佳结果。鲁棒的校准需要更多的现场数据，尤其是对于大而复杂的岬角而言，它们与用于开发的理想模型大不相同。旁路表达式可用于为各种岬角类型提供波浪绕过的第一遍估计值。这将对在多石的和隐蔽的海岸线上工作的沿海管理人员，科学家和工程师有用。