Sediment Transport and Morphological Evolution In Rivers In Response to Catastrophic Dam-Break Floods

0510830智力成绩：非恒定流泥沙运动的研究主要集中在非恒定流方面，尽管有大量的泥沙运动发生在非恒定流中，但非恒定流泥沙运动仍然是水文科学中的一个开放性研究问题，这主要是由于完全耦合的水流泥沙方程固有的数学复杂性，以及在实验测量中遇到的技术困难。更复杂的数学方法的可用性（Tsai 2002，2003，2005和Tsai和Yen 2001，2003; Tsai和Kuai 2004 a，B; Kuai等人，2004）表明，现在是重新审视非恒定流中泥沙输移问题的时候了。这项试验研究的成功将为研究水沙运动的耦合和试验溃坝洪水等高度不稳定流中泥沙输移的新方法铺平道路。研究假设和科学目标：这项基础研究的主要目标是量化与大坝通过相关的水面和床面高程以及泥沙浓度的随时间变化的变化，研究的基本假设是：入流过程的时间依赖性影响泥沙输移，因此标准的恒定流公式不能提供准确的输沙量估计值;在分析河床对快速变化的入流过程的水力响应时，与水流的时间尺度相比，有关河床抬升的时间尺度可能不再长，因此只有水流和泥沙方程的完全耦合模型才能正确地描述这种现象。本文的工作是非恒定输沙研究的第一阶段。（1）对于天然河道溃坝引发的特大洪水，解耦定常均匀流模型方法能否取得满意的模拟结果？(2)与快速变化的水流（如溃坝洪水）相比，有关河床高程变化的时间尺度是否仍然很长？(3)如何量化和解释实验室和现场观测中证实的泥沙浓度、摩擦系数、流速和深度之间的相位差？该研究旨在提供一个改进的物理框架来研究天然河流中的泥沙输运和形态演变，以应对高度不稳定的水流，如溃坝引发的洪水。主要研究任务包括模型开发、校准、验证和比较、收集和汇编现有的实验室和现场数据，以及评估这一形态过程中涉及的关键水流和沉积物参数。首先，研究成果将为联邦和州机构的政策决策提供有用的信息，例如评估河流和溪流的运输能力，估计河床和河岸侵蚀和沉积的环境影响，并协助评估设计方案。研究结果的潜在应用包括水坝和水库的设计，洪泛区分析和管理，以及大洪水事件期间可能的最大冲刷估计。其次，这个项目也将对本科生和研究生的教育水平产生重大影响。这项基础研究的结果将被整合到科学、数学和工程的教学中，以使更广泛的学生群体受益。

0510830Intellectual Merit: Extensive sediment transport research has been accomplished primarily insteady flow, although significant amounts of sediment movement occur in unsteady flow.Despite some early attempts, sediment transport in unsteady flow remains an open researchquestion in hydrologic sciences, mainly due to the inherent mathematical complexities in thefully coupled flow and sediment equations, and the technical difficulties encountered inexperimental measurements. Availability of a more sophisticated mathematical approach (Tsai2002, 2003, 2005 and Tsai and Yen 2001, 2003; Tsai and Kuai 2004 a,b; Kuai et al. 2004)suggests that it is time to revisit the problem of sediment transport in unsteady flow. Success ofthis pilot study would pave the way for a new approach to investigating the coupling of waterand sediment movement and to experimenting with transport of sediment in highly unsteadyflows such as dam-break induced floods.Research Hypotheses and Scientific Objectives: The major objectives of this basic research areto quantify the time-varying changes in water- and bed-surface elevation and sedimentconcentration associated with the passage of a dam-break induced flood and to examine thevalidity of the quasi-steady uniform flow assumption in unsteady sediment transport modeling.The basic hypotheses guiding the proposed research are that time dependence of inflowhydrograph affects sediment transport so that standard steady flow formulas will not provideaccurate estimates of sediment discharge, and that when analyzing the hydraulic response of abed to rapidly changing inflow hydrographs, the time scale of interest concerning bed elevationmay no longer be long compared to that of the flow so that only fully coupled models of flowand sediment equations would properly characterize the phenomena. The work proposed here isconsidered the first phase of our unsteady sediment transport research. Specifically, this researchaims to address the following issues: (1) For the simulation of a catastrophic flood induced bythe breach of a dam in a natural river, can the decoupled and steady uniform flow modelingapproach still yield satisfactory results? (2) Is the time scale of interest concerning bed elevationchange still long compared to that of the flow in rapidly changing flows such as dam-breakinduced floods? (3) How can the phase difference among sediment concentration, friction factor,flow velocity and depth, as evidenced in laboratory and field observations, be quantified andinterpreted? The proposed research intends to provide an improved physical framework to studysediment transport and morphological evolution in natural rivers in response to a highly unsteadyflow such as dam-break induced floods. The main research tasks involve model development,calibration, verification and comparison, collection and compilation of existing laboratory andfield data, and evaluation of critical flow and sediment parameters involved in thismorphological process.Broader Impacts: The most significant and broadest impacts of this project are twofold. First,research outcomes will provide useful information for policy decision-making by federal andstate agencies, such as evaluation of transport capacities of rivers and streams, estimation ofenvironmental impacts of riverbed and bank erosion and deposition, and assistance in theevaluation of design alternatives. Potential applications of the research results include design ofdams and reservoirs, floodplain analysis and management, and estimation of possible maximumscour during large flood events. Secondly, this proposed project would also have significanteducational impact on both undergraduate and graduate levels. Findings of this fundamentalresearch will be integrated into the teaching of science, math and engineering to benefit a broaderstudent community.