Alongshore Advective Acceleration in the Surf Zone

概述：本项目主要研究由冲波带水深变化引起的沿岸流变化和平流加速度。沿岸流的变化和冲浪带形态变化之间的反馈可能是沿岸均匀入射波的海滩上的冲浪带形态的演变至关重要。确定由冲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精确的海岸演变和污染输送模型非常重要。现场证据表明，平流加速度有助于显着的动量平衡也可能导致新的理论和模型为海岸线changes.Intellectual优点：分析和数值研究表明，沿岸平流加速度可能是重要的surfzone裂流，沿岸流曲流，分散，泥沙运移和形态演变。最近的数值模型模拟表明，沿岸平流加速度可以是大的相对于其他条款的深度和时间平均surfzone动量平衡的海滩沿岸水深变化小至10厘米。然而，现场测量表明，沿岸流预测以及忽略平流加速度的简化方程。此外，除了附近的强离岸流，现场观测显示，沿岸冲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来解释。也有可能是基于观测的沿岸流梯度的估计值偏低，因为流量最大值和最小值由于原位传感器之间相对较大的空间间隔而无法解决。另外，数值模式，这是敏感的摩擦系数，可能高估了平流加速度。将获得波浪强迫、压力梯度和冲浪区流动的密集分布观测结果，以校准数值模型模拟。现场测量将被用来估计平流加速度和现场测试的模型将被用来探讨在沿岸不均匀的冲浪区水深测量存在的平流加速度的原因。特别是，观测和模拟将解决以下问题：沿岸平流加速度重要吗？沿岸流梯度和平流加速度的模式预测准确吗？是什么导致了沿岸平流加速度？通过结合现场观测，旨在测量流动变化的空间尺度上的小surfzone水深变化与数值模型模拟，调查人员将能够解决这些问题的重要性和原因的沿海岸平流加速度的海滩附近均匀incident wave.Broader影响：美国海岸和海滩保护协会（ASBPA，http://www.asbpa.org）关注的是，美国人感兴趣的海岸工程无法获得现场经验。因此，将与ASBPA和感兴趣的工程公司建立伙伴关系，为本科生、应届毕业生和从事沿海职业的年轻专业人员提供实地培训。特别是，将提供两个项目：为目前受雇于沿海咨询和工程公司的年轻专业人员提供为期2至3周的以实地考察为重点的实习，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。已经有十几家公司表示对实习生项目感兴趣，并表示愿意支持他们的员工参加拟议中的项目。学生奖学金将类似于之前由首席调查员Raubenheimer进行的Swashzone奖学金，该奖学金已导致几名学生在沿海工程公司获得职位。实习生和学生将与调查人员合作，以获得实地观察，并改善近岸过程的模型，这反过来又将改善沿海管理，帮助保护沿海社区，并维持沿海资源。

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.