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首页> 外文学位 >Shelf sediment dispersal mechanisms and deposition on the Waiapu River shelf, New Zealand.
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Shelf sediment dispersal mechanisms and deposition on the Waiapu River shelf, New Zealand.

机译：新西兰怀阿普河架子上的架子沉积物扩散机制和沉积。

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摘要

The Waiapu River, located on the North Island of New Zealand, drains a small catchment and has one of the highest sediment yields in the world. The river delivers most of its annual sediment load during floods into energetic coastal waters. These conditions are favorable for producing multiple sediment transport mechanisms, including transport in positively and negatively buoyant freshwater plumes, gravitydriven flows, and resuspension.; Analyses of Waiapu River shelf seabed data showed that multiple transport mechanisms influence strata formation. Fluvial sediments are initially deposited at water depths shallower than 80 m before being remobilized and deposited at greater water depths. Over the last 100 years fine sediments were retained mainly at water depths between 60 and 190 m, and accounted for 24% of the fluvial load. High shelf accumulation rates (0.2--3.3 cm/yr) were sufficient to preserve pulsed event layers, which were identified by low excess 210Pb and terrestrial delta 13C. Additionally, high subsidence rates on the tectonically active shelf likely influences modern depositional patterns.; A three-dimensional numerical model was used to address the mechanisms by which sediment escaped the shelf and to assess the relative importance of the various transport mechanisms. The simulation was able to reproduce time-averaged currents, near-bed sediment concentrations, and bed shear stresses at a tripod deployed off the river mouth at 60 m water depth. Gravity-driven transport was most important on the inner and mid-shelf, whereas dilute transport became more important beyond 65 m depth. Sediments escaped the shelf via dilute suspension to the north of the Waiapu River mouth.; Sensitivity experiments showed that transport pathways and depositional patterns were sensitive to floc fraction, waves and currents, and sediment load. Increasing the floc fraction resulted in increased wave-supported gravity-driven transport relative to dilute transport and increased shelf deposition. Coherence between energetic waves and floods increased the importance of wave-supported gravity-flows and shifted initial deposition offshore. Wave-induced bed shear stress increased gravity-driven transport, whereas current-induced bed shear stress increased dilute transport. Deforestation over the last 150 years, which has resulted in an increase annual suspended load, may have resulted in increased shelf sediment retention.
机译：怀亚普河位于新西兰北岛，排泄了一个小流域，是世界上沉积物产量最高的国家之一。在洪水泛滥到充满活力的沿海水域期间，这条河每年的大部分泥沙负荷都来自河流。这些条件有利于产生多种沉积物传输机制，包括以正浮力和负浮力的淡水羽流，重力驱动的水流和再悬浮物进行运输。怀阿普河架子海床数据的分析表明，多种输运机制影响地层的形成。河流沉积物最初被沉积在小于80 m的水深处，然后才被转移并沉积在更大的水深中。在过去的100年中，细小沉积物主要保留在60至190 m的水深处，占河流负荷的24％。高的架子堆积速率（0.2--3.3 cm / yr）足以保存脉冲事件层，这可通过低的过量210Pb和地面三角洲13C来确定。另外，构造活动层架上的高沉降率可能会影响现代沉积模式。一个三维数值模型被用来解决沉积物从架子上逸出的机理，并评估各种输送机理的相对重要性。该模拟能够重现时间平均电流，近床沉积物浓度和在水深60 m处离开河口的三脚架处的床剪应力。重力驱动的运输在内部和中层架上最为重要，而稀疏运输在65 m深度以上变得更为重要。沉积物通过稀悬浮物逸出到威阿普河河口以北。敏感性实验表明，输运途径和沉积方式对絮凝率，波浪和水流以及泥沙负荷很敏感。相对于稀运输，增加絮凝分数导致增加了波浪支撑的重力驱动运输，并增加了架子沉积。高能波浪与洪水之间的相干性增加了波浪支撑重力流的重要性，并使初始沉积物转移到了海上。波浪引起的床剪应力增加了重力驱动的输运，而电流引起的床剪应力增加了稀释输运。在过去的150年中，森林砍伐导致每年的悬浮负荷增加，可能导致架子上的沉积物滞留量增加。

著录项

  • 作者

    Kniskern, Tara A.;

  • 作者单位

    The College of William and Mary.;

  • 授予单位 The College of William and Mary.;
  • 学科 Geology.; Physical Oceanography.
  • 学位 Ph.D.
  • 年度 2007
  • 页码 283 p.
  • 总页数 283
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 地质学;海洋物理学;
  • 关键词

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