Sand re-suspension events in a high energy infragravity swash zone
Sand re-suspension events in a high energy infragravity swash zone
复制标题
高能次重力冲沙带中的沙子再悬浮事件
DOI：
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发表时间：
1999
期刊：
影响因子：
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通讯作者：
Geraldine A. Rooker
中科院分区：
文献类型：
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作者：
P. Osborne;Geraldine A. Rooker
在新西兰奥克兰以西的高能量耗散海滩的前滩测量了悬浮泥沙浓度 (SSC)、流体速度和形态响应。冲刷再悬浮事件表现出与上冲和反冲阶段相关的独特时间结构。 SSC > 50 gl -1 与向岸传播斜孔下浅水中的大加速度、湍流和高流速相关。 SSC 从最初的峰值开始迅速下降，然后随着水深增加而逐渐下降，直到上升结束时达到最大值。随着反洗加速，SSC逐渐增大，在反洗快结束时，在水流迅速变稀和加速的情况下达到峰值。水流是超临界的，会发生水力跳跃，并且在反冲事件结束时经常会形成不稳定的反沙丘床形，导致 SSC 急剧增加。随着斜盘最大深度的增加，事件平均 SSC 系统性下降。上升事件下的峰值SSC往往比反冲洗事件下的峰值更大，特别是在冲刷区边缘附近。对内冲浪区和斜流区之间过渡处的速度和 SSC 进行的交叉谱分析证实，主要传输发生在次重力频率下。净输送可能对上冲和反洗循环中 SSC 和速度之间的相位角的微小变化以及冲刷循环中床条件的变化敏感。
Suspended sediment concentration (SSC), fluid velocity and morphological response were measured on the foreshore of a high energy dissipative beach west of Auckland, New Zealand. Swash re-suspension events exhibit a distinct temporal structure associated with both the uprush and backwash phases. SSC of > 50 gl -1 is associated with large accelerations, turbulence, and high flow speeds in shallow water under shoreward propagating swash bores. SSC decreases rapidly from the initial peak and then more gradually as water depth increases to a maximum at the end of the uprush. SSC increases gradually as the backwash accelerates, and then reaches a peak under the rapidly thinning and accelerating flow near the end of the backwash. Flows are super-critical, hydraulic jumps occur and unstable anti -dune bedforms often develop near the end of backwash events resulting in sharp increases in SSC. Event averaged SSC declines systematically as maximum depth of swash increases. Peak SSC tends to be larger under uprush events than backwash events particularly near the margins of the swash zone. Cross-spectral analysis of velocity and SSC at the transition between the inner surf zone and swash zone confirms that the dominant transport occurs at infragravity frequencies. Net transport is potentially sensitive to small variations in the phase angle between SSC and velocity in the uprush and backwash cycle as well as to the variability in bed conditions during swash cycles.