Synchronization of Transport And Supply: The Role of Nearshore Processes In Beach-Dune Interaction

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。现有的海滩-沙丘模型没有考虑沉积物如何以及何时被转移到后海岸，在那里它们可以被风运输。相反，现有模型在很大程度上将沙丘形态的区域变化归因于海滩坡度和泥沙收支的固定约束。缺乏这方面的资料仍然是发展海滩-沙丘相互作用理论的主要障碍，这种理论可以构成有效预测模型的基础，可以跨尺度和在不同地点之间转换。最近的（过程尺度）输运研究表明，由于在滩面上的输运限制，沉积物的输运在空间上是可变的，在时间上是间歇性的。虽然这些研究已经确定了对沉积物运输和交换的各种控制，但预测海滩-沙丘系统演变的能力仍然有限，主要是因为海滩面往往被视为静态运输面，而不考虑供应。了解海滩-沙丘过程对于理解堰洲岛如何从热带风暴和飓风中恢复具有重要意义，这反过来又决定了下一次风暴如何影响岛屿。该项目由德克萨斯农工大学的Christopher Houser博士主持，将确认并量化近岸过程和形态变化对海滩和沙丘之间沉积物交换的作用。随着海滩状态的演变，海滩和沙丘之间的泥沙交换取决于海滩面上输运势和有效泥沙的同步。本研究的具体目标是：(1)量化与波浪强迫和近岸沙洲形态变化有关的海滩表面形态和体积的随时间变化；(2)识别和量化与运输势（风速和风向）有关的风成输送的随时间控制（例如海滩几何形状、湿度、滞后等）；(3)确定海滩输沙和沙丘堆积是否依赖于上前滩和后滩近岸过程输沙势和有效供沙量的同步。这项研究代表了对海滩-沙丘系统理解的根本变化。虽然过程地貌学家习惯于将小尺度的过程视为地形的组成部分，但他们通常认为这些过程独立于集体背景，即它们所处的特定景观，从而对地形的演变有意义。沙丘恢复需要沉积物首先通过近岸（冲浪和冲刷）过程输送到后海岸，然后通过风输送到沙丘。尽管沙丘恢复对下一次风暴的影响很重要，但除了少数例外，人们很少关注风暴后沙丘恢复的机制。表征控制堰洲岛沙丘恢复速度和机制的因素对海岸管理者非常有兴趣，他们需要一种方法来预测下一次风暴期间预期的影响类型，并确定是否需要恢复海滩或沙丘以保护财产和基础设施。在这方面，这项研究为关注海滩和沙丘管理各个方面的地理学家、工程师和规划人员提供了好处。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Existing beach-dune models do not consider how and when sediment gets transferred to the backshore where they become available for transport by the wind. Rather, existing models largely ascribe regional variations in dune morphology to fixed constraints on the beach slope and sediment budget. The lack of information in this regard remains a central barrier to the development of a theory of beach-dune interaction that can form the basis of effective predictive models that can be translated across scales and between sites. Recent (process-scale) transport studies have shown that the transfer of sediment is both spatially variable and temporally intermittent as a result of transport limitations across the beachface. While these studies have identified varied controls on sediment transport and exchange, there remains a limited capacity to predict the evolution of beach-dune systems, largely because the beachface tends to be viewed as a static transport surface and without regards to supply. Understanding beach-dune processes has important implications for understanding how barrier islands recover from tropical storms and hurricanes, which in turn determines how the next storm impacts the island. This project, conducted by Dr. Christopher Houser at Texas A&M University will confirm and quantify the role of nearshore processes and morphological change on the exchange of sediment between the beaches and dunes. The exchange of sediment between the beach and dune depends on the synchronization of transport potential and available sediment on the beachface as the beach-state evolves. The specific goals of this study are: (1) to quantify time-dependent variations in the morphology and volume of the beachface in relation to the wave forcing and changes in the morphology of the nearshore bars, (2) to identify and quantify the time-dependent controls on aeolian transport (e.g. beach geometry, moisture, lag, etc.) in relation to the transport potential (wind speed and direction), and (3) to determine if the delivery of sediment from the beach and accumulation in the dune depends on the synchronization of transport potential and available supply of sediment deposited by nearshore processes in the upper-foreshore and backshore. This study represents a fundamental change in understanding of the beach-dune system. While process-geomorphologists are accustomed to thinking about small-scale processes as the building blocks of landforms, they typically consider these processes independent of the collective context, the specific landscape in which they are acting, to make sense to the evolution of landforms. Dune recovery requires sediment to be delivered first to the backshore by nearshore (surf and swash) processes and then delivered to the dune by the wind. With few exceptions, little attention has been paid to the mechanisms of dune recovery following storms, despite the importance of dune recovery to the impact of the next storm. Characterizing the factors that control the rate and mechanism of barrier island dune recovery is of great interest to coastal managers who need a means to predict the type of impact expected during the next storm and in determining if beach or dune restoration is required to protect property and infrastructure. In this respect, the study provides benefits to the communities of geographers, engineers and planners concerned with various aspects of beach and dune management.