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首页> 外文期刊>Estuarine Coastal and Shelf Science >Bathymetric evolution of the Mersey Estuary, UK, 1906-1997: causes and effects
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Bathymetric evolution of the Mersey Estuary, UK, 1906-1997: causes and effects

机译：1906-1997年，英国默西河口的等深线演变：因果关系

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This paper examines how a continuous series of measurements and model studies have developed our understanding of the evolving interactions between tidal dynamics, sediment regime and bathymetry of the Mersey Estuary―among the most intensively monitored worldwide. This includes familiar assessments of the capabilities of fine-resolution 3-D models but is here extended to examine historical changes in tides, sediments and estuarine bathymetries. A century of bathymetric surveys indicates a net loss of estuarine volume of about 0.1%, or 1 million cubic metres, per year. In contrast, sea level rise of 1.2 mm a~(-1) represents only a 0.02% annual increase. This relative stability persists in a highly dynamic regime with suspended sediment concentrations exceeding 2000 mg l~(-1) and spring tide fluxes of order 200000 t. Detailed analyses of the bathymetric sequences indicate most significant changes occur in the upper estuary and in inter-tidal zones. A long period, up to 63 years, of tidal elevation records (in the lower estuary) shows almost no changes to the predominant M_2 and S_2 constituents. The 3-D numerical model accurately reproduces both these elevation constituents and corresponding cross-sectional distributions of currents. Simulation accuracies reduce upstream due to cumulative errors associated with relatively unstable bathymetries and increasing sensitivities to the bed stress coefficients. Impacts from increases in river flows of up to two or three times the long-term mean value can only be detected in the upper estuary. A detailed examination of sediment fluxes utilised a numerical simulation of conditions over a cross-section in the 'Narrows', the 10 km by 1.5 km prismatic entrance channel. The limited mobility of coarse sediments was contrasted with the near-continuously suspended nature of the finest clay. A sensible match between the net sedimentation rates indicated by the model and the net observed deposition rate was found to occur for silty sand corresponding directly with evidence from dredging records and from direct sampling. While the model indicated sedimentation rates might increase by up to a factor of ten for much finer particles, such occurrences are likely to be restricted by the limited availability of such material in the adjacent coastal zone. The controlling mechanism for this import of fine sediments is via tidal pumping, the nature of which depends critically on the phase lead of tidal currents relative to elevation. However, since this phase lead is determined by the large scale tidal energy balance of the estuary, the conclusion is that stability of the overall tidal dynamics, the associated sediment regime and bathymetry are likely to co-exist and evolve slowly as indicated by the observed annual decrease in net volume. Suggestions are included for monitoring strategies in other estuaries to provide insight into such dynamics-sediment-bathymetry inter-relationships.
机译：本文探讨了一系列连续的测量和模型研究如何使我们对潮汐动力学，泥沙状况和默西河口测深仪之间不断发展的相互作用了解，这是全球监测最密集的部分。这包括对高分辨率3D模型功能的熟悉评估，但在此扩展为检查潮汐，沉积物和河口测深仪的历史变化。一个世纪的测深研究表明，每年河口的净损失约为0.1％，即一百万立方米。相比之下，海平面上升1.2 mm a〜（-1）仅代表每年0.02％的增长。这种相对稳定性在高动态范围内持续存在，悬浮沉积物浓度超过2000 mg l（（-1），春季潮汐通量为200000 t。对测深序列的详细分析表明，最明显的变化发生在上河口和潮间带。长达63年的长期潮汐记录（在河口下部）显示，主要的M_2和S_2成分几乎没有变化。 3-D数值模型可以准确地再现这些高程成分和相应的电流横截面分布。由于与相对不稳定的测深法相关的累积误差和对床应力系数的敏感性增加，模拟精度降低了上游。河流流量增加的影响可能是长期平均值的2到3倍，只能在河口上游发现。泥沙通量的详细检查利用了“狭窄”（10 km x 1.5 km的棱形入口通道）横截面条件的数值模拟。粗颗粒沉积物有限的流动性与最细粘土的近乎连续悬浮的性质形成对比。对于由疏sand记录和直接采样提供的证据，直接对应于粉砂的模型表明，模型指示的净沉降速率与净观测沉降速率之间存在合理的匹配。虽然该模型表明，对于更细的颗粒，沉积速率可能会增加多达十倍，但这种现象很可能会受到相邻沿海地区此类物质有限供应的限制。细粒沉积物的这种进口控制机制是通过潮汐泵，其性质关键取决于潮汐流相对于海拔的相位超前。但是，由于该相的超前是由河口的大规模潮汐能平衡决定的，因此得出的结论是，总体潮汐动力学的稳定性，相关的沉积物状态和测深法可能共存并缓慢发展，如观测到的那样。净交易量逐年减少。在其他河口中还包括监测策略的建议，以提供对此类动力学-沉降-测深法相互关系的深入了解。

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