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

合作研究：CROSSTEX - 陆上酒吧运动的实验研究

• 批准号: 0351297
• 负责人: James Kirby
• 金额: $ 25.32万
• 依托单位: University of Delaware
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-06-01 至 2009-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0351297&HistoricalAwards=false
• 关键词: Collaborative; Research; CROSSTEX; Experimental; Study

ABSTRACTOCE-0351297Cross-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.

跨海岸沉积物输运过程在大多数海滩的侵蚀和加积的年度周期中起着至关重要的作用。我们对强烈风暴事件期间侵蚀过程的理解已经取得了很大的进步，模型在预测风暴坝的形成和离岸迁移方面表现出了合理的技能。对加积过程，特别是沙洲向陆地的迁移，还没有得到类似的理解。因此，跨海岸运输过程的预测模型在预测侵蚀和加积事件的任何扩展序列的形态变化方面表现出很少的技能。目前缺乏了解的部分原因是缺乏可用的数据集。在该领域，在加积事件期间的剖面演变测量需要在适当的时间有一个详细的测量计划和足够的流体动力学仪器，以允许过程为基础的模型进行测试。Duck '94实验提供了一个这样的数据集。然而，在现场的跨岸过程可以被掩盖或改变的横向扩散的大沿岸运输量，并可以进一步复杂化的二维水深变化的演变，导致沿岸变异的跨岸运输模式。大规模的实验室实验已经在近场规模进行，消除了对结垢问题的大部分关注，并提供了一个孤立的看纯粹的跨海岸过程。然而，现有的数据集不提供足够长的时间来观察在加积事件期间沙洲的向岸运动，并且不提供提供预测模型的校准和盲测所需的多个事件的测量。PI将进行一项扩展的跨岸形态实验，以检查在增积波条件下平行于海岸的砂坝向岸迁移。实验将在俄勒冈州州立大学的大型波浪水槽设施中进行。实验计划将主要研究悬移质与推移质运输方式的相对作用。还将包括是否“塞流”（砂床上层的质量故障）在滨岸沙坝运动事件中起着重要作用。将广泛使用流体动力学模型（基于Boussinesq或非线性缓坡公式）来设计实验条件，并协助选择仪器位置。所获得的数据集将用于检验水动力模型和沉积物输运模型的预测，这两个模型在很长一段时间内都是由水动力模型驱动的。该数据集将充分描述与一个重要时期的滨岸沙坝运动相关的水动力和泥沙输运机制，将为评估目前缺乏的现代泥沙输运模型提供试验基础。通过访问这样的数据库，可以改进基于过程的预测模型，这可以显着提高海岸工程和近岸海洋学社区预测美国海岸线侵蚀和加积的季节性变化的能力。人口稠密的沿海地区这一项目的成果将通过在同行评审的期刊上发表文章、在国际和国家会议上作介绍、为对数据集感兴趣的科学家和行业成员及沿海管理人员举办讲习班、将结果纳入课堂材料以及本科生的参与等方式广泛传播。