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

[510830]智力优势：广泛的泥沙输移研究主要是在非定常流中完成的，尽管大量的泥沙运动发生在非定常流中。尽管有一些早期的尝试，但在水文科学中，非定常流动中的泥沙输移仍然是一个开放的研究问题，主要是由于流动和泥沙完全耦合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（Tsai2002, 2003, 2005和Tsai and Yen 2001, 2003; Tsai and Kuai 2004 a,b; Kuai et al. 2004）表明，是时候重新审视非定常流动中的泥沙输移问题了。这项初步研究的成功将为研究水和泥沙运动耦合的新方法铺平道路，并为在高度不稳定的水流（如溃坝引起的洪水）中试验泥沙的运输铺平道路。研究假设和科学目标：本基础研究的主要目标是量化溃坝洪水引起的水面、床面高程和沉积物浓度随时间的变化，并检验准稳定均匀流假设在非定常输沙模型中的有效性。指导本研究的基本假设是：入流线的时间依赖性会影响输沙量，因此标准的定常流公式无法提供准确的输沙量估算；在分析河床对快速变化的入流线的水力响应时，与水流的时间尺度相比，有关河床高程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恰当地描述这种现象。本文提出的工作被认为是我们非定常输沙研究的第一阶段。具体而言，本研究旨在解决以下问题：(1)对于自然河流溃坝引发的特大洪水的模拟，解耦稳定均流建模方法是否仍能得到令人满意的结果？(2)与溃坝洪水等快速变化的水流相比，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野外观测证明的泥沙浓度、摩擦系数、流速和深度之间的相位差？提出的研究旨在提供一个改进的物理框架，以研究自然河流对高度不稳定流量（如溃坝引起的洪水）的反应中沉积物的运输和形态演变。主要研究任务包括模型开发、校准、验证和比较，现有实验室和现场数据的收集和汇编，以及对这一形态过程中涉及的关键水流和泥沙参数的评估。更广泛的影响：本项目最重要和最广泛的影响是双重的。首先，研究成果将为联邦和州政府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，评估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，洪泛区的分析和管理，以及大洪水事件时可能的最大冲刷估计。其次，这个建议项目也会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.