Alongshore Advective Acceleration in the Surf Zone

冲浪区的近岸平流加速

• 批准号: 1332705
• 负责人: Britt Raubenheimer
• 金额: $ 76.29万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-07-01 至 2017-11-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1332705&HistoricalAwards=false
• 关键词: Alongshore; Advective; Acceleration; Surf; Zone

Overview: This project focuses on the alongshore flow variations and advective accelerations owing to surfzone bathymetric variations. Feedbacks between alongshore flow variations and surfzone morphological changes may be critical to the evolution of surfzone morphology on beaches with alongshore uniform incident waves. Determining the magnitude of the alongshore advective accelerations and flow variability resulting from surfzone features is important to developing accurate models for coastal evolution and transport of pollution. Field evidence that the advective acceleration contributes significantly to the momentum balance also may lead to new theories and models for shoreline change.Intellectual Merit: Analytical and numerical studies suggest that alongshore advective acceleration may be important to surfzone rip currents, alongshore flow meanders, dispersion, and sediment transport and morphological evolution. Recent numerical model simulations indicate that alongshore advective acceleration can be large relative to other terms in the depth- and time-averaged surfzone momentum balance on beaches with alongshore bathymetric variations as small as ten centimeters. However, field measurements have shown that alongshore flows are predicted well with simplified equations that neglect advective accelerations. Furthermore, except near strong rip currents, field observations show relatively small alongshore variations in alongshore surfzone flows. The simplified equations may reproduce observed velocities accurately because the advective acceleration term is balanced by an alongshore pressure gradient term, or because advective acceleration is accounted for by the parameterized bottom friction coefficient. It also is possible that the observation-based estimates of alongshore flow gradients are biased low because flow maxima and minima are not resolved owing to the relatively large spatial separations between in situ sensors. Alternatively, the numerical models, which are sensitive to the friction coefficient, may overpredict the advective acceleration. Densely distributed observations of wave forcing, pressure gradients, and surfzone flows will be obtained to calibrate numerical model simulations. The field measurements will be used to estimate advective acceleration and the field-tested model will be used to explore the causes of the advective accelerations in the presence of alongshore inhomogeneous surfzone bathymetry. In particular, the observations and simulations will address the following questions: Is alongshore advective acceleration important? Are model predictions of alongshore flow gradients and advective acceleration accurate? And what causes alongshore advective acceleration? By combining field observations designed to measure flow variations at the spatial scales of small surfzone bathymetric variations with numerical model simulations, the investigators will be able to address these questions about the importance and causes of alongshore advective accelerations on beaches with near uniform incident waves.Broader Impacts: The American Shore and Beach Preservation Association (ASBPA, http://www.asbpa.org) is concerned that Americans interested in coastal engineering are not able to obtain field experience. Thus, a partnership with ASBPA and interested engineering firms will be established to provide field training to undergraduates, recent graduates, and young professionals embarking on coastal careers. In particular, two programs will be offered: 2- to 3-week-long fieldwork-focused internships for young professionals currently employed in coastal consulting and engineering firms, and 6-month-long fellowships for students interested in coastal engineering careers. More than a dozen companies already have expressed interest in the internships, and have offered to support their employees to participate in the proposed program. The student fellowships would be similar to the Swashzone Fellowships previously conducted by the lead investigator, Raubenheimer, which have led to several students receiving positions in coastal engineering firms. The interns and students will work with the investigators to obtain field observations, and to improve models for nearshore processes, which in turn will improve coastal management, help protect coastal communities, and sustain coastal resources.

概述：该项目重点研究由于海面区测深变化引起的沿岸流动变化和平流加速度。沿岸水流变化和冲浪区形态变化之间的反馈对于具有沿岸均匀入射波的海滩上冲浪区形态的演变可能至关重要。确定由海浪带特征引起的沿岸平流加速度和流量变化的大小对于开发沿海演化和污染输送的准确模型非常重要。现场证据表明，平流加速对动量平衡有显着贡献，也可能导致海岸线变化的新理论和模型。 智力价值：分析和数值研究表明，沿岸平流加速可能对表面带离岸流、沿岸流曲流、扩散、以及沉积物迁移和形态演化。最近的数值模型模拟表明，在海滩上，沿岸平流加速度相对于深度和时间平均冲浪区动量平衡中的其他项可能很大，沿岸测深变化小至十厘米。然而，现场测量表明，使用忽略平流加速度的简化方程可以很好地预测沿岸流动。此外，除了附近较强的离岸流外，现场观测显示，沿岸海浪带流的沿岸变化相对较小。简化的方程可以准确地再现观测到的速度，因为平流加速度项由沿岸压力梯度项平衡，或者因为平流加速度由参数化的底部摩擦系数考虑。由于现场传感器之间相对较大的空间间隔而无法解析流量最大值和最小值，因此基于观测的沿岸流量梯度估计值也可能偏低。或者，对摩擦系数敏感的数值模型可能会高估平流加速度。将获得波浪强迫、压力梯度和海面带流的密集分布观测值，以校准数值模型模拟。现场测量将用于估计平流加速度，现场测试模型将用于探索在沿岸不均匀海面区测深存在的情况下平流加速度的原因。特别是，观测和模拟将解决以下问题：沿岸平流加速重要吗？沿岸水流梯度和平流加速度的模型预测准确吗？是什么导致了沿岸平流加速？通过将旨在测量小冲浪区测深变化空间尺度上的流量变化的现场观测与数值模型模拟相结合，研究人员将能够解决有关近均匀入射波海滩上沿岸平流加速度的重要性和原因的问题。影响：美国海岸和海滩保护协会（ASBPA，http://www.asbpa.org）担心对海岸工程感兴趣的美国人无法获得现场经验。因此，将与 ASBPA 和感兴趣的工程公司建立合作伙伴关系，为本科生、应届毕业生和从事沿海职业的年轻专业人士提供现场培训。特别是，将提供两个项目：为目前在沿海咨询和工程公司工作的年轻专业人员提供为期 2 至 3 周的以实地工作为重点的实习，以及为对沿海工程职业感兴趣的学生提供为期 6 个月的奖学金。已有十几家公司表达了对实习的兴趣，并表示愿意支持其员工参与拟议的计划。这些学生奖学金类似于首席研究员 Raubenheimer 之前开展的 Swashzone 奖学金，该奖学金已帮助几名学生在沿海工程公司获得了职位。实习生和学生将与调查人员合作，获得实地观察结果，并改进近岸过程模型，从而改善沿海管理，帮助保护沿海社区并维持沿海资源。