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This thesis concerns the computation of bed adjustments of equilibrium in alluvial meandering streams. It is assumed that the channel centerlines follow sine-generated curves, the banks are rigid, and the steady-state flow is turbulent and sub-critical. The flow width is assumed to remain constant in the streamwise direction, and the flow width-to-depth ratio is large (>=15, say). The bed material is cohesionless and homogeneous. The purpose of the thesis is to develop and test a numerical model for the computation of bed development, given the aforementioned idealized conditions. The model comprises: 1- an initial bed topography generator, to generate the bed at time t = 0 of the calculations; 2- the vertically-averaged hydrodynamic model of Zhang (2007) to calculate the flow fields; and 3- a sediment transport model to relate the bed deformation to the flow. Both the initial bed topography generator (expression of the deformed bed surface) and the numerical sediment transport model based on the sediment transport continuity equation are original and developed entirely by the author. The resulting model is computationally very efficient. In contrast to previous works on the theoretical determination of bed deformation, the beds at the beginning of the calculations may represent any stage of the development process, and not necessarily the initial flat bed. The bed deformation was tested for several test cases, devised on the basis of laboratory runs available in the literature. These include Run ME-2 by Hasegawa (1983) in a 30-degree-channel, Run 3 by Binns (2006) in a 70-degree-channel and the run by Termini (1996) in a 110-degree-channel. The erosion/deposition patterns of the computed equilibrium bed topographies were found to be in reasonable agreement with their measured counterparts. However, as evidenced by the difference plots included in this thesis, in detail there are substantial differences between the computed and measured equilibrium beds, especially in the regions near the banks. As a by-product of the present thesis, the functions representing the parameters required by the hydrodynamic model of Zhang (2007) were also evaluated. In particular, the present results suggest that the coefficient Alpha-q appearing in the expression of the local friction factor (used in the flow model of Zhang 2007) depends on the flow width-to-depth ratio and bed roughness to a much larger extent than previously thought. Considering this, a generalization of the expression of Alpha-q due to El-Tahawy (2004) (and adopted by Zhang 2007 in her model) is proposed. Future work should be carried out to address the application of the present model to real river conditions, including generalizations to irregular meandering plan shapes, unsteady-state flows and non-homogenous bed materials. / Thesis (Ph.D, Civil Engineering) -- Queen's University, 2008-12-19 21:32:06.645

京都大学 / 新制・課程博士 / 博士(工学) / 甲第23479号 / 工博第4891号 / 新制||工||1764(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 立川 康人, 准教授 市川 温, 教授 角 哲也 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

Sediment has profound effects on water quality. Correspondingly, water quality modeling often needs sediment transport modeling. However, simplified descriptive sediment transport was originally employed for water quality modeling, and the linkage between sediment transport models and water quality models is less developed. Therefore, the main purposes of this study were to develop general methods of coupling sediment transport and water quality models and to improve sediment transport modeling for water quality modeling. Linkage of sediment transport and water quality was discussed and a comprehensive sediment transport literature review was conducted. SEDDEER (Sediment Deposition and Erosion), a stand-alone sediment and contaminant fate and transport model, which simulates one water box and the underlying multiple sediment bed layers, was developed. SEDDEER for Visual Basic for Application (SEDDEER_VBA) was written in VBA. SEDDEER for FORTRAN (SEDDEER_FOR) is the corresponding FORTRAN model. To improve WASP in terms of sediment transport, SEDDEER_FOR was incorporated into the WASP TOXI7 module as the starting point to generate the coupled WASP model (WASP_SEDDEER). Verification and validation of SEDDEER_VBA were conducted prior to model application and incorporation. A comprehensive model test was performed to show that SEDDEER_FOR is computationally identical to SEDDEER_VBA. Simple tests were carried out to verify the fluxes across the sediment-water interface and ensure that the coupling of the WASP water column and SEDDEER bed models is correct. The testing results indicated that these models were verified and/or validated. SEDDEER was used to evaluate the effects of sediment on contaminant transport. WASP_SEDDEER, WASP7.4, and EFDC were applied to Mobile Bay to demonstrate the capabilities of WASP_SEDDEER, and WASP_SEDDEER produced a reasonable and consistent modeling result. The results of the study indicated that SEDDEER can be used for one-box sediment and contaminant fate and transport modeling, and also incorporated into water quality models. In addition, WASP_SEDDEER coupling was implemented correctly and can be applied to the real world. Finally, study results show that sediment affects contaminant fate and transport mostly by external forcing and flow conditions, and contaminant fate and transport varies with different sediment and contaminant characteristics and sediment transport processes.

The complex interaction between flow, vegetation and sediment drives the never settled changes of riverine system. Vegetation intercepts rainfall, adds resistance to surface flow, and facilitates infiltration. The magnitude and timing of flood flow are closely related to the watershed vegetation coverage. In the meantime, flood flow can transport a large amount of sediment resulting in bank erosion, channel degradation, and channel pattern change. As climate changes, future flood frequency will change with more intense rainfalls. However, the quantitative simulation of flood flow in vegetated channel and the influence of climate change on flood frequency, especially for the arid and semi-arid Southwest, remain challenges to engineers and scientists. Therefore, this research consists of two main parts: simulate unsteady flow and sediment transport in vegetated channel network, and quantify the impacts of climate change on flood frequency. A one-dimensional model for simulating flood routing and sediment transport over mobile alluvium in a vegetated channel network was developed. The modified St. Venant equations together with the governing equations for suspended sediment and bed load transport were solved simultaneously to obtain flow properties and sediment transport rate. The Godunov-type finite volume method is employed to discretize the governing equations. Then, the Exner equation was solved for bed elevation change. Since sediment transport is non-equilibrium when bed is degrading or aggrading, a recovery coefficient for suspended sediment and an adaptation length for bed load transport were used to quantify the differences between equilibrium and non-equilibrium sediment transport rate. The influence of vegetation on floodplain and main channel was accounted for by adjusting resistance terms in the momentum equations for flow field. A procedure to separate the grain resistance from the total resistance was proposed and implemented to calculate sediment transport rate. The model was tested by a flume experiment case and an unprecedented flood event occurred in the Santa Cruz River, Tucson, Arizona, in July 2006. Simulated results of flow discharge and bed elevation changes showed satisfactory agreements with the measurements. The impacts of vegetation density on sediment transport and significance of non-equilibrium sediment transport model were accounted for by the model. The two-dimensional surface flow model, called CHRE2D, was improved by considering the vegetation influence and then applied to Santa Cruz River Watershed (SCRW) in the Southern Arizona. The parameters in the CHRE2D model were calibrated by using the rainfall event in July 15th, 1999. Hourly precipitation data from a Regional Climate Model (RCM) called Weather Research and Forecasting model (WRF), for three periods, 1990-2000, 2031-2040 and 2071-2079, were used to quantify the impact of climate change on the magnitude and frequency of flood for the Santa Cruz River Watershed (SCRW) in the Southern Arizona. Precipitation outputs from RCM-WRF model were bias-corrected using observed gridded precipitation data for three periods before directly used in the watershed model. The watershed model was calibrated using the rainfall event in July 15th, 1999. The calibrated watershed model was applied to SCRW to simulate surface flow routing for the selected three periods. Simulated annual and daily maximum discharges are analyzed to obtain future flood frequency curves. Results indicate that flood discharges for different return periods are increased: the discharges of 100-year and 200-year return period are increased by 3,000 and 5,000 cfs, respectively.