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首页> 外文期刊>Ocean Dynamics >Fine sediment transport by tidal asymmetry in the high-concentrated Ems River: indications for a regime shift in response to channel deepening
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Fine sediment transport by tidal asymmetry in the high-concentrated Ems River: indications for a regime shift in response to channel deepening

机译：高浓度埃姆斯河中潮汐不对称引起的精细泥沙输送：响应河道加深，政权发生转移的迹象

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This paper describes an analysis of the observed up-river transport of fine sediments in the Ems River, Germany/Netherlands, using a 1DV POINT MODEL, accounting for turbulence-induced flocculation and sediment-induced buoyancy destruction. From this analysis, it is inferred that the net up-river transport is mainly due to an asymmetry in vertical mixing, often referred to as internal tidal asymmetry. It is argued that the large stratification observed during ebb should be attributed to a profound interaction between turbulence-induced flocculation and sediment-induced buoyancy destruction, as a result of which the river became an efficient trap for fine suspended sediment. Moreover, an asymmetry in flocculation processes was found, such that during flood relative large floes are transported at relative large flow velocity high in the water column, whereas during ebb, the larger floes are transported at smaller velocities close to the bed- this asymmetry contributes to the large trapping mentioned above. The internal tidal asymmetry and asymmetry in flocculation processes are both driven by the pronounced asymmetry in flow velocities, with flood velocities almost twice the ebb values. It is further argued that this efficient trapping is the result of a continuous deepening of the river, and occurs when concentrations in the river become typically a few hundred mg/l; this was the case during the 1990 survey analyzed in this paper. We also speculate that a second regime shift did occur in the river when fluid mud layers become so thick that net transport rates are directly related to the asymmetry in flow velocity itself, probably still in conjunction with internal asymmetry as well. This would yield an efficient mechanism to transport large amounts of fine sediment far up-river, as currently observed.
机译：本文描述了使用1DV POINT模型对德国Ems河，荷兰/荷兰细颗粒沉积物上流观测的分析，解释了湍流引起的絮凝和沉积物引起的浮力破坏。从该分析可以推断出净的上河输送主要是由于垂直混合中的不对称性，通常被称为内部潮汐不对称性。有人认为，在退潮期间观察到的较大分层应该归因于湍流引起的絮凝作用和沉积物引起的浮力破坏之间的深刻相互作用，因此，河流成为了有效的细小悬浮沉积物陷阱。此外，在絮凝过程中发现了不对称性，例如，在洪水期间，较大的絮凝物以较高的流速在水柱中以较高的速度运输，而在退潮期间，较大的絮凝物以接近床层的较小速度运输。上面提到的大陷阱。絮凝过程中的内部潮汐不对称性和不对称性均由流速的明显不对称性驱动，洪水速度几乎是退潮值的两倍。进一步认为，这种有效的捕集是河水不断加深的结果，并在河水浓度典型地达到几百毫克/升时发生。本文分析的1990年调查就是这种情况。我们还推测，当流体泥浆层变得如此稠密以至于净输水速率与流速本身的不对称性直接相关时，河流中确实发生了第二次政权转移，可能还与内部的不对称性有关。如目前观察到的那样，这将产生一种有效的机制，将大量细小的沉积物运到上游。

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