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Flow dynamics in the transition zone from estuarine tidal to fluvial regime in the Santee River, SC, USA.

机译：美国南卡罗来纳州桑蒂河从河口潮汐到河流域过渡带的流动动力学。

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摘要

Estuaries are important systems that link fresh, inland waters to oceanic salt water, where they act to deliver large amounts of nutrients, sediments and pollutants into the ocean. Traditionally, the study of estuarine systems has been marked by difficulty owing to the complex hydrodynamics influenced by strong bathymetric changes, changes in tidal range, intricate geomorphology, among other factors; thus beginning to unravel the complexities of estuarine hydrodynamics will help to illuminate the nature of estuaries as well as to provide a foundation for their further study. In this study I focus on the transition zone from tidal to fluvial regime, which is defined as an area where tidal and river discharges are comparable. Recently, the transition zone has been the focus of attention as an important region within an estuary.;Tides are subject to frictional dissipation as they propagate inland through estuaries and river channels. Previous studies suggest that there is an enhanced tidal dissipation in the transition zone from a tidal to fluvial regime when the tidal flux and river discharge become comparable. The aim of this study is to understand the kinematics and dynamics within the transition zone. In particular, I hypothesize that there is an enhanced tidal dissipation in the transition zone due to (i) additive effects of tidal and river currents subject to the quadratic bottom friction, and (ii) to the presence of variable topography and enhanced bathymetric gradients in the transition zone. I analyzed time series of velocity profiles and bottom pressure that resolve the along-channel depth-averaged momentum balance in the transition zone of the Santee River, SC, USA. The following momentum balance terms are estimated: inertia (local acceleration), along-channel advective acceleration, pressure gradient, and bottom friction terms. Instruments were deployed in a 1-km long river reach characterized by a decreasing depth in the upstream direction from over 4 m to less than 2 m. Tides in the study area are predominantly semi-diurnal, flood-dominant. The leading terms in the depth-averaged momentum balance are found to be inertia, pressure gradient, and bottom friction. The pressure gradient and inertia dominate the momentum balance during the flood and subsequent current reversal from flood to ebb. However, during the ebb the pressure gradient is nearly balanced by bottom friction. A dissipative term is defined as a residual of inertia, advection, and pressure gradient force terms. I found that the dissipative term is comparable with the bottom friction term under steady river discharge. However, the bottom friction term underestimates the dissipative term when the river discharge exhibits abrupt variations. This yields a record-mean with a linear regression slope of 0.54. I hypothesize that the lateral eddy viscosity also contributes to tidal dissipation, especially when the pressure gradient force increases. Although tides are flood-dominant, most of the dissipation occurs during the ebb due to a superposition of comparable fluvial and tidal currents.
机译：河口是将淡水，内陆水与海洋盐水连接起来的重要系统，在这些系统中，河口将大量养分，沉积物和污染物输送到海洋中。传统上，由于强大的测深变化，潮差变化，复杂的地貌以及其他因素的影响，复杂的水动力使河口系统的研究面临困难。因此，开始揭示河口水动力学的复杂性将有助于阐明河口的性质，并为他们的进一步研究提供基础。在这项研究中，我重点研究了从潮汐到河流域的过渡带，这是潮汐和河流流量可比的区域。近年来，过渡区已成为河口内的重要区域，成为人们关注的焦点。潮汐通过河口和河道向内陆传播时，容易受到摩擦耗散的影响。先前的研究表明，当潮汐流量和河流流量变得可比时，从潮汐到河流域过渡带的潮汐消散会增强。这项研究的目的是了解过渡带内的运动学和动力学。特别是，我假设过渡区域的潮汐耗散增加，原因是：（i）受到二次底摩擦的潮汐和河流潮流的累加效应，以及（ii）地形变化和水深梯度的增加过渡区。我分析了速度曲线和底部压力的时间序列，以解决美国南卡罗来纳州桑提河过渡带沿通道深度平均动量平衡。估计以下动量平衡项：惯性（局部加速度），沿通道对流加速度，压力梯度和底部摩擦项。仪器部署在1公里长的河段中，其特征是上游方向的深度从4 m以上减少到2 m以下。研究区的潮汐以半日为主，以洪水为主。深度平均动量平衡的主要术语是惯性，压力梯度和底部摩擦。压力梯度和惯性支配着洪水期间的动量平衡，以及随后的电流从洪水到退潮的过程。但是，在退潮期间，压力梯度几乎被底部摩擦所平衡。耗散项定义为惯性，对流和压力梯度力项的残差。我发现在稳定的河流流量下，耗散项与底部摩擦项可比。但是，当河流流量呈现突变时，底部摩擦项会低估耗散项。这将产生具有线性回归斜率0.54的记录均值。我假设横向涡流粘度也有助于潮汐消散，特别是当压力梯度力增加时。尽管潮汐以洪水为主，但由于可比的潮汐流和潮汐流叠加，大部分消散发生在退潮期间。

著录项

  • 作者

    Torres-Garcia, Legna M.;

  • 作者单位

    University of South Carolina.;

  • 授予单位 University of South Carolina.;
  • 学科 Physical Oceanography.;Geomorphology.
  • 学位 M.S.
  • 年度 2014
  • 页码 61 p.
  • 总页数 61
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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