Fluid acceleration effects on suspended sediment transport in the swash zone
Fluid acceleration effects on suspended sediment transport in the swash zone
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DOI：
10.1029/2003jc001943
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发表时间：
2003-11
影响因子：
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通讯作者：
J. Puleo;K. Holland;N. Plant;D. Slinn;D. Hanes
中科院分区：
文献类型：
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作者：
J. Puleo;K. Holland;N. Plant;D. Slinn;D. Hanes
利用在高能量陡坡滩冲刷带测量的悬沙浓度和流体速度，研究了流体加速度对悬沙运移的重要性。斜流加速度在下坡重力加速度的一半左右时几乎是恒定的，但有两个重要的例外。我们观察到，在斜冲旋回开始时，有强烈的、短暂的加速上升期，在斜冲旋回结束时，有减速反冲期（两者的量级都大约是预期下坡重力加速度的两倍）。有趣的是，悬挂载荷的峰值跟随加速度的异常，这在几乎对称（量级）的总体平均速度时间序列中并不明显。悬浮载荷值在与海岸传播湍流孔或斜坡前缘相关的加速冲升期间最大。在反冲洗期间，悬浮载荷通常没有那么大。相应的，通过泥沙浓度和流速测量得到的悬沙输沙率与一个修正的泥沙输沙模型（该模型包含了由于水流加速而提高输沙率的物理机制）进行了最好的比较。修正后的输沙模型将总体均方根预测误差降低了35%，并将冲升输沙率的预测峰值在冲沙旋回中移得更早，与观测值的拟合更好。这些发现表明，包含加速项可能解释了物理机制，包括通常与上冲加速部分相关的膛内湍流和水平压力梯度。
[1] Suspended sediment concentrations and fluid velocities measured in the swash zone of a high-energy steep beach were used to investigate the importance of fluid accelerations to suspended sediment transport. Swash flow acceleration was nearly constant at about one-half downslope gravitational acceleration with two important exceptions. We observed strong, short-lived periods of accelerating uprush at the beginning of the swash cycle and decelerating backwash at the end of the swash cycle (magnitudes of both approximately twice that of the expected downslope gravitational acceleration). Interestingly, spikes in suspended load followed the anomalies in acceleration in a way that was not apparent from the nearly symmetric (in magnitude) ensemble averaged velocity time series. Suspended load values were largest during accelerating uprush associated with the shoreward propagating turbulent bore or swash front. During backwash, suspended loads were generally not as large. Correspondingly, suspended sediment transport rates obtained from the sediment concentration and velocity measurements showed best comparisons with a modified sediment transport model that includes a physical mechanism for enhancing transport rates due to flow acceleration. The modified sediment transport model reduced the overall root-mean square prediction error by up to 35% and shifted the predicted peak in uprush sediment transport rate earlier in the swash cycle, resulting in a better fit to the observations. These findings suggest that the inclusion of the acceleration term may account for physical mechanisms that include bore turbulence and horizontal pressure gradients typically associated with the accelerating portion of uprush.