Representation of the marine environment is key for reliable coastal hydrodynamic models. This study investigates the implications of common depth-averaged model configuration choices in sufficiently characterising seabed geometry and roughness. In particular, applications requiring a high level of accuracy and/or exhibiting complex flow conditions may call for greater detail in marine environment representation than typically adopted in coastal models. Ramsey Sound, a macrotidal strait in Pembrokeshire, Wales, UK is considered as a case study. The site contains various steeply inclined bathymetric features, including a submerged pinnacle named Horse Rock and a rocky reef called “The Bitches”. The available energy in Ramsey Sound’s tidal currents has attracted attention from tidal energy developers. There is interest in accurately modelling the energetic hydrodynamics surrounding its pronounced bathymetry. The coastal flow solver Thetis is applied to simulate the flow conditions in Ramsey Sound. It is shown that notable prominent bathymetric features in the strait influence localised and, most importantly, regional hydrodynamic characteristics. “The Bitches” consistently accelerate flow in the strait while Horse Rock induces a notable wake structure and flow reversals. The model is calibrated against bed- and vessel-mounted Acoustic Doppler Current Profiler (ADCP) observations, by altering seabed roughness parameterisations. A spatially variable and locally scaled Manning coefficient based on diverse seabed classification observations is found to improve model performance in comparison to uniformly applied constants, the latter a more common approach. The local impact of altering the Manning coefficient configuration is found to be greatest during spring flood periods of high velocity currents. Meanwhile, the effect of coarsening the computational mesh around bathymetric features towards values more typically applied in coastal models is investigated. Results indicate severe misrepresentation of seabed geometry and subsequent wake hydrodynamics unless refined to a mesh element size that adequately represents Horse Rock and “The Bitches”.

海洋环境的表征是可靠的沿海水动力模型的关键。这项研究调查了常见的深度平均模型配置选择对充分表征海床几何形状和粗糙度的影响。特别地，与沿海模型中通常采用的相比，要求高精确度和/或表现出复杂流动条件的应用可能需要在海洋环境表示中提供更多细节。案例研究认为，英国威尔士彭布罗克郡的大潮海峡拉姆齐峡湾（Ramsey Sound）是一个案例研究。该站点包含各种陡峭的测深特征，包括一个名为Horse Rock的水下石峰和一个名为“ The Bitches”的礁石。Ramsey Sound的潮流中的可用能量引起了潮汐能开发商的关注。有必要对围绕其明显的测深法的高能流体动力学进行精确建模。沿海流量求解器提斯用于模拟Ramsey Sound中的流动条件。结果表明，海峡中明显的深海测深特征影响了局部，最重要的是影响了区域水动力特性。“母狗”持续加速海峡两岸的水流，而马岩石则引起了明显的尾流结构和水流逆转。通过更改海床粗糙度参数设置，针对安装在床和船上的声学多普勒电流剖面仪（ADCP）观测值对模型进行了校准。发现基于空间变化和局部缩放的曼宁系数是基于各种海床分类观测结果的，与统一应用的常数相比，后者可以提高模型性能，后者是更常见的方法。发现在高速流的春季洪水期间，改变曼宁系数配置的局部影响最大。同时，研究了将测深要素周围的计算网格粗化为更通常在沿海模型中应用的值的效果。结果表明，除非精制到足以代表马岩石和“母狗”的网格元素尺寸，否则海床几何形状和随后的尾流流体动力学的表述会很不正确。