Collaborative Research: CROSSTEX - An Experimental Study of Onshore Bar Movement

跨岸泥沙输运过程在大多数海滩侵蚀和增生的年幕式循环中起着至关重要的作用。我们对强风暴事件期间的侵蚀过程的理解已经取得了很大的进步，模型在预测风暴棒的形成和离岸迁移方面已经显示出合理的技能。对吸积过程，特别是向陆地迁移的过程，还没有一个平行的认识。因此，跨海岸运输过程的预测模型在预测任何扩展的侵蚀和增生事件序列的形态变化方面表现出很少的技巧。目前缺乏理解的部分原因是缺乏可用的数据集。在现场，在吸积过程中测量剖面演变需要有详细的测量计划和足够的流体动力学仪器，以便在适当的时间测试基于过程的模型。Duck '94实验提供了一个这样的数据集。然而，野外的跨岸过程可能被大的海岸输运量的横向扩散所掩盖或改变，并可能因二维水深变化的演变而进一步复杂化，从而导致跨岸输运模式的海岸变异性。在近场范围内进行了大规模的实验室实验，消除了对规模问题的大部分担忧，并提供了纯粹的跨海岸过程的孤立观察。然而，现有的数据集并不能对吸积事件期间的海岸运动提供足够长的观察，也不能提供对预测模型进行校准和盲测所需的多个事件的测量。PI将进行扩展的跨海岸形态实验，以检查在吸积波条件下滨平行沙洲的滨向迁移。实验将在俄勒冈州立大学的大波水槽设施中进行。实验计划将主要研究悬浮荷载与层载运输模式的相对作用。此外，还包括“栓流”（砂床上层的质量破坏）是否在滨沙洲运动事件中起重要作用。将广泛使用水动力模型（基于Boussinesq或非线性缓坡公式）来设计实验条件并协助选择仪器放置位置。获得的数据集将用于测试水动力模型和泥沙输运模型的预测，这些模型是由水动力模型驱动的。该数据集将充分描述与一个重要的滨沙坝运动时期相关的水动力学和泥沙输运机制，将为评估目前缺乏的现代泥沙输运模型提供一个试验基础。基于过程的预测模型的改进可以显著提高海岸工程和近岸海洋学社区预测美国海岸线侵蚀和增生的季节变化的能力美国人口稠密的沿海地区。该项目的成果将通过以下方式广泛传播：同行评议期刊上的出版物、在国际和国家会议上的报告、为对数据集感兴趣的科学家以及为工业界成员和沿海管理人员举办的讲习班、将结果列入课堂材料以及由本科生参加。

ABSTRACTOCE-0351153Cross-shore sediment transport processes play a crucial role in the annual episodic cycles of erosion and accretion on most beaches. Great strides have been made in our understanding of erosional processes during intense storm events, and models have shown reasonable skill in predicting storm bar formation and offshore migration. A parallel understanding of accretional processes, particularly the landward migration of bars, has not yet been obtained. Consequently, predictive models of cross-shore transport processes exhibit little skill in predicting morphology change for any extended sequence of erosional and accretional events. Part of the lack of present understanding stems from a paucity of available data sets. In the field, measurement of profile evolution during an accretional event requires having both a detailed surveying program and sufficient hydrodynamic instrumentation in place at the right time in order to allow testing of process based models. The Duck '94 experiment has provided one such data set. However, cross-shore processes in the field can be masked or altered by the lateral diffusion of the large longshore transport volume, and can be further complicated by the evolution of two dimensional bathymetric variations, leading to longshore variability of the cross-shore transport pattern. Large scale laboratory experiments have been conducted at near-to-field scale, eliminating most of the concerns over scaling issues and providing an isolated look at purely cross-shore processes. However, the existing data sets do not provide a long enough look at the shoreward movement of bars during accretional events, and do not provide measurements of the multiple events that are needed to provide both calibration and a blind test of predictive models. The PI's will conduct an extended cross-shore morphology experiment to examine the shoreward migration of shore-parallel sand bars under accretional wave conditions. The experiments will be conducted in the large wave flume facility at Oregon State University. The experimental program will primarily examine the relative roles of suspended load versus bedload modes of transport. Also included will be whether "plug-flow" (mass failure of the upper layer of the sand bed) plays a significant role during shoreward bar movement events. Extensive use will be made of hydrodynamic models (based on Boussinesq or nonlinear mild-slope formulations) to design experimental conditions and assist in choice of instrument placement. The acquired data set will be used to test the predictions of both the hydrodynamic models and the sediment transport models, which are driven for extended periods by the hydrodynamic models. This data set which will adequately describe the hydrodynamics and sediment transportmechanisms associated with a significant period of shoreward bar movement, will provide a test base for evaluating modern sediment transport models which is presently lacking. The improvement of process-based predictive models which could result from access to such a data base could markedly increase the coastal engineering and nearshore oceanography communities' ability to predict the seasonal variability of shoreline erosion and accretion in the U.S.'s heavily populated coastal zones. The results of this project will be disseminated broadly through publications in peer-reviewed journals, presentations at international and national conferences, workshops for scientists interested in the data set and for industry members and coastal managers, inclusion of the results in classroom material, and participation by undergraduate students.