Analysis of Cross-Shore Movement of Natural Longshore Bars and Material Placed to Create Longshore Bars
Analysis of Cross-Shore Movement of Natural Longshore Bars and Material Placed to Create Longshore Bars
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发表时间：
1992-09
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通讯作者：
M. Larson;N. Kraus
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作者：
M. Larson;N. Kraus
这项研究开发了疏浚材料形成的近岸护堤设计的经验预测公式。这种护堤是以长线状沙洲的形式放置的，预计会起到天然沙洲的作用。这项研究考察了北卡罗来纳州达克市天然岸滩的跨岸运动。从1981年到1989年，海滩剖面调查数据大约每隔两周提供一次，同时还有对波浪条件的测量。鸭子通常有两个沙洲，一个在大约4到5米深的外沙洲，一个在1到2米深的内沙洲。这些沙洲往往在风暴期间移至近海，在海浪较低时移至岸上。介绍了一种用于野外数据分析的明确定义条形特征的方法。该方法使用了一种平衡剖面形状，该剖面形状定义为随着离岸距离的增大而减小的颗粒尺寸。对沙洲的运动进行了分析，如果修正各准则中乘性经验系数的取值，则作者以前建立的预报海滩冲淤的准则是适用的。结果表明，沙洲在岸上移动的可能性比先前估计的要大，这表明通过近岸护堤的形成有利于海滩滋养的波浪条件可能范围更广。从东海岸海滩开发的预测标准成功地描述了加州银滩公园护堤的岸上运动观测。用无量纲参数表示的准则似乎适用于主要通过波浪作用修改堤坝和已建造的水下护堤的场地。
This study develops empirical predictive expressions for design of nearshore berms formed of dredged material. Such berms are placed in the form of long linear sand bars and are expected to behave as natural bars. The study examines the cross-shore movement of natural longshore bars at Duck, North Carolina. Beach profile survey data are available at approximately 2-week intervals from 1981 to 1989, together with measurements of the wave conditions. Two bars are typically present at Duck, an outer bar at approximately the 4- to 5- m depth and an inner bar at 1- to 2-m depth. These bars tend to move offshore during storms and onshore during periods of lower waves. A method is introduced to define bar-type features unambiguously for analysis of field data. The method uses an equilibrium profile shape defined in terms of decreasing grain size with distance offshore. Analysis is made of bar movement, and criteria previously developed by the authors to predict beach erosion and accretion are found applicable if the value of a multiplicative empirical coefficient in each criterion is modified. The results show that onshore movement of bars is more probable than previously estimated, indicating a wider possible range of wave conditions favorable for beach nourishment through creation of nearshore berms. The predictive criteria developed from the east coast beach successfully described the observed onshore movement of a berm placed at Silver Strand Park, California. The criteria, expressed as nondimensional parameters, appear to have applicability to sites where bars and constructed submerged berms are modified primarily by wave action.