CAREER: Swash Zone Sediment Transport

该CAREER项目旨在通过实验室和现场工作，使用一种新的推移质层（非常接近静止床面）泥沙输运测量装置，提高对冲流区泥沙输运过程的理解和预测能力。冲刷带是靠近海岸线的区域，波浪驱动的水流交替地在海滩表面上下冲刷，并最终消耗它们的能量。因此，冲流过程是海岸形态变化发生的基本机制之一（例如海岸线对海平面变化的反应）。由于大部分人口居住在海岸线附近，全球海平面在过去十年中以3毫米/年的速度上升（IPPC WGII，2007），近85%的美国桑迪海岸线受到侵蚀（Thornton等人，2000年），有一个真实的社会需求，以更好地了解这些过程。目前的预测模型是非常有限的，他们无法准确地描述推移质输运的意义。这一限制主要是由于不存在与时间相关的推移质输运的可靠测量，尽管时间积分收集器数据表明推移质通常是主要的输运模式（Horn和Mason，1994年）。本计画将以下列步骤来探讨量化冲淤区推移质输移的困难任务：（1）测试并使用一种新颖的推移质感测器，以获得冲淤区不易获得的推移质量测;（2）量化推移质与悬移质的相对重要性，作为海滩坡度、波浪条件与冲淤相位的函数，以发展新的输移公式;（3）研究冲刷带泥沙输移信号中泥沙平流和冲刷边界交换的作用;（4）利用实验室和野外资料可靠地确定冲刷带泥沙输移的参数。其结果将是更好地了解推移质输运在重塑海滩表面方面的作用，从而加强对海岸地貌变化的预测，并设计更有效和更经济的减缓程序。这项研究将扩大对海岸沉积物输运物理学的理解，并将导致显著提高预测诸如海滩侵蚀和海滩营养等海岸现象的能力性能更一般地说，测量技术和数据集将大大提高对流体力学领域广泛感兴趣的含颗粒边界层过程的科学理解。研究结果将通过综合和持续的外联活动传播给工程师和非专业人员。特拉华州的工程外展办公室，当地学校教师和教育课程专家将合作，并协助启动“海滩在教室”的高中学生和教师培训研讨会使用16英尺的便携式波浪水槽外展计划。这项研究将支持少数民族本科暑期实习生与教师和研究生并肩进行研究。实习招聘将通过与NSF赞助的LSAMP计划合作在附近的HBCU进行。

This CAREER project aims to advance understanding and predictive capability of sediment transport processes occurring in the swash zone through laboratory and field efforts using a new measurement device for sediment transport in the bedload layer (very near the at-rest bed level). The swash zone is the area near the shoreline where wave-driven flows alternately wash up and down the beach face and ultimately expend their energy. Thus, swash processes are one of the fundamental mechanisms by which coastal morphological change happens (e.g. shoreline response to changing sea level). With much of the population living near the coastline, global sea levels rising at a rate of 3 mm/yr over the last decade (IPPC WGII, 2007) and nearly 85% of sandy U.S. coastlines eroding (Thornton et al., 2000), there is a real societal demand for better understanding of these proceses. Current predictive models are extremely limited by their inability to accurately characterize the significance of bedload transport. This limitation is primarily due to the fact that no reliable measurements of time-dependent bedload transport exist, even though time-integrated trap data demonstrates that bedload is often the dominant transport mode (Horn and Mason, 1994). This project will approach the difficult task of quantifying swash-zone bedload transport with the following steps:(1) test and use a novel bedload sensor to obtain elusive bedload measurements in the swash zone; (2) quantify the relative importance of bedloadand suspended load as a function of beach slope, wave conditions and swash phase to develop new sediment transport formulations; (3) investigate the role of sediment advection and exchange across thesurf/swash boundary in the swash-zone sediment transport signal; and (4) utilize laboratory and field data to reliably parameterize swash-zone sediment transport. The result will be an improved understanding of the role of bedload transport in reshaping the beach face leading to enhanced predictions of coastal morphologic change and the design of more effective and economical mitigation procedures.Broader Impacts: This study will broaden understanding of the physics of coastal sediment transport and will lead to significant improvement in the ability to predict coastal phenomena such as beach erosion and beach nourishment performance. More generally, the measurement techniques and data sets will greatly improve scientific understanding of particle-laden boundary layer processes that are of broad interest in the area of fluid mechanics. Research results will be disseminated to engineers and lay people through integrated and ongoing outreach activities. The University of Delaware's Engineering Outreach Office, local school teachers and education curriculum experts will collaborate and assist in initiating the "beach in a classroom" outreach program for high school students and teacher training workshops using a 16-foot portable wave flume. The study will support a minority undergraduate summer intern in performing research side-by-side with faculty and graduate students. Recruitment for the internship will be conducted at nearby HBCU's through collaboration with the NSF-sponsored LSAMP Program.