Morphodynamics of dune erosion and rebuilding on macrotidal beaches of British Columbia

本研究考察了不列颠哥伦比亚省北部海岸的高能量、森林和浮木内衬的海滩-沙丘系统的沉积和地貌反应。这些系统与加拿大其他系统的不同之处在于极端的风、浪和潮状况，以及控制其形式和功能的不同人为和生态因素（例如，浮木堵塞，快速殖民植被）。这些系统对已知的北太平洋气候变率信号也很敏感，如厄尔尼诺和太平洋年代际涛动（PDO），并且不像五大湖或加拿大大西洋地区的其他系统那样经历海冰、冻土或植被减少等冬季影响。主要目标是测量和模拟近地面气流、表面粗糙度和沉积物输运之间的关系，从而提高对这些系统如何响应海岸侵蚀（通过波浪作用）和随后的重建（通过风沙输运）的认识。区域海洋-大气过程通过控制当地侵蚀水位的频率和大小以及通过陆上风沙运输进行的沙丘重建来驱动海滩-沙丘形态动力学。长期的地貌响应和侵蚀重建机制的潜在变化将与气候变率和变化事件有关。为此，我们将探讨3个研究假设。首先，潮汐阶段和风向通过“取沙”效应影响海滩-沙丘的动力学，这种效应控制着向海滩输送的沙子的数量。这一假设是最近一个理论模型的基础，该模型将用现场数据进行验证。其次，浮木堵塞和林分提供了额外的粗糙度和储存能力，以捕获海滩上的风吹沙。这些特点提供了一个缓冲，以防止极端的水位和海浪的攻击，并可以创建新的沙丘。第三，气候变率事件影响风、波和水位状态，并与海岸沙丘的季节和年际形态响应相关。因此，海岸侵蚀和沙丘重建的局地尺度动力学与气候变率和变化有关。

This research examines the sedimentary and geomorphic responses of high-energy, forested and driftwood lined beach-dune systems on BC's north coast. These systems are distinct from others in Canada for extreme wind, wave & tide regimes and for different anthropogenic & ecological factors (e.g., driftwood jams, rapidly colonizing vegetation) that control their form and function. These systems are also sensitive to known climate variability signals of the NE Pacific such as El Nino and the Pacific Interdecadal Oscillation (PDO) and do not experience winter season effects such as sea ice, frozen ground or vegetation declines like other systems on the Great Lakes or in Atlantic Canada. The main objective is to measure and model the relations between near-surface airflow, surface roughness and sediment transport so as to enhance knowledge on how these systems respond to coastal erosion (via wave action) and subsequent rebuilding (via aeolian sand transport). Regional ocean-atmosphere processes drive beach-dune morphodynamics by controlling the local frequency & magnitude of erosive water levels and dune rebuilding via onshore aeolian (wind) sand transport. Longer-term geomorphic responses and potential changes in the erosion-rebuilding regime will be related to climate variability & change events. To do this, 3 research hypotheses will be explored. First, tide stage & wind direction affect beach-dune dynamics via a 'fetch' effect that controls the amount of sand delivered to the beach. This hypothesis is the basis of a recent theoretical model that will be tested with field data. Second, driftwood jams & forest stands provide additional roughness & storage capacity to trap windblown sand on beaches.  These features provide a buffer against extreme water levels & wave attack and can create new dunes. Third, climate variability events affect wind, wave & water level regimes and can be correlated to seasonal to interannual morphological responses of coastal dunes. It follows that local-scale dynamics of coastal erosion and dune rebuilding are related to climate variability & change.