Towards Practical Models Of Continental River Dynamics With The Saint Venant Equations

Simulating dynamic river networks at continental scales has been a long-term goal of the hydraulic and hydrologic communities. However, difficulties in computational costs, data availability, and numerical stability have been major obstacles in applying the full, dynamic Saint-Venant equations over such scales - i.e., creating simulations of "Continental River Dynamics." Recent research has provided progress in addressing both computational costs and data availability, but numerical instability for large-scale models has been problematic (until addressed by the study herein). Prior methods for ensuring numerical stability for short river reaches are inadequate for large-scale Saint-Venant simulations due to their expensive computational cost or incompatibility with numerical schemes designed for large-scale systems. The present research addresses and provides solutions for three major sources of numerical instability in river network modeling: (i) poorly defined initial conditions, (ii) non-smooth source terms in the governing equations, and (iii) channel geometry that is insufficiently smooth or perhaps improperly defined. In the first part of this study, a robust steady Saint-Venant model (SSM) is developed. This new model applies a concept from graph-theory to provide consistent initial conditions for every computational element in a large-scale river network simulation - which is a necessary step for efficiently starting a large-scale unsteady simulation. The present SSM method can effectively generate the initial condition for different scale of river network up to 5000 x faster than the traditional method, and save up to 99% of unnecessary numerical iterations. In the second part of this work, the problem of non-smooth source terms in the governing equations is solved. A new “reference slope” concept is proposed to ensure smooth source terms and eliminate potential numerical oscillations. It is shown that a simple algebraic transformation of channel geometry can provide a smooth reference slope while preserving the correct cross-sectional flow area and the piezometric pressure gradient that drives the flow. The reference slope method ensures a Lipschitz-continuous source term while maintaining all the underlying complexity of the real-world geometry. The method systematically alleviates the oscillatory numerical behaviors provoked by non-smooth bed slope (although it cannot address problems associated with non-smooth cross-sectional area). In the third section of this work, a new sweep-search algorithm (SSA) is developed to identify locations in a network where changes in the channel cross-sectional geometry are responsible for numerical convergence failures that prevent large-scale simulation of a large-scale river network. By taking advantage of computational speed in SSM (developed in the first part of this research), the SSA can recursively examine the numerical stability of each computational element in the network. The new SSA approach provides for automated identification of problem locations in large river network data sets, which is necessary to effectively apply the full dynamic Saint-Venant equations to large-scale river networks. In summary, the research in this study provides further building blocks toward making Continental River Dynamics simulations a reality

Comprehensive text on the fundamentals of modeling flow and sediment transport in rivers treating both physical principles and numerical methods for various degrees of complexity. Includes 1-D, 2-D (both depth- and width-averaged) and 3-D models, as well as the integration and coupling of these models. Contains a broad selection

A definitive guide for accurate state-of-the-art modelling of free surface flows Understanding the dynamics of free surface flows is the starting point of many environmental studies, impact studies, and waterworks design. Typical applications, once the flows are known, are water quality, dam impact and safety, pollutant control, and sediment transport. These studies used to be done in the past with scale models, but these are now being replaced by numerical simulation performed by software suites called “hydro-informatic systems”. The Telemac system is the leading software package worldwide, and has been developed by Electricité de France and Jean-Michel Hervouet, who is the head and main developer of the Telemac project. Written by a leading authority on Computational Fluid Dynamics, the book aims to provide environmentalists, hydrologists, and engineers using hydro-informatic systems such as Telemac and the finite element method, with the knowledge of the basic principles, capabilities, different hypotheses, and limitations. In particular this book: presents the theory for understanding hydrodynamics through an extensive array of case studies such as tides, tsunamis, storm surges, floods, bores, dam break flood waves, density driven currents, hydraulic jumps, making this a principal reference on the topic gives a detailed examination and analysis of the notorious Malpasset dam failure includes a coherent description of finite elements in shallow water delivers a significant treatment of the state-of-the-art flow modelling techniques using Telemac, developed by Electricité de France provides the fundamental physics and theory of free surface flows to be utilised by courses on environmental flows Hydrodynamics of Free Surface Flows is essential reading for those involved in computational fluid dynamics and environmental impact assessments, as well as hydrologists, and bridge, coastal and dam engineers. Guiding readers from fundamental theory to the more advanced topics in the application of the finite element method and the Telemac System, this book is a key reference for a broad audience of students, lecturers, researchers and consultants, right through to the community of users of hydro-informatics systems.

This thesis has been devoted to three different problems related to the morphodynamics of rivers. The first of them concerns sediment transport, for which a two-phase flow model has been proposed, valid in both viscous and turbulent regimes. As a main result, this model describes the transition from bed load to suspended load when the Shields number is increased. The second subject was the formation of bars. We revisited the linear stability analysis of these bedforms in order to emphasize the role played by the saturation length. We have shown that this saturation length controls the transition from ripples to bars. The third and most developed aspect of this PhD work was dedicated to the formation of meanders. By means of 3D RANS equations, we have performed a detailed description of hydrodynamics in a channel with both modulated bed and undulating banks. Coupled to sediment transport, the linear stability analysis of the problem gives predictions for the growth rate, the migration velocity and the shape of the bed for given meandering banks of wavenumber k. These predictions are in quantitative agreement with experimental data we obtained in a small flume: the entire dispersion relation is fitted with reasonable parameters of the modeling, but also the bed modulation is correctly reproduced. On the qualitative sicle, we have identified the mechanism responsible for this instability. This mechanism is different to thàt proposed by Einstein and it is also different to the resonance proposed by Blondeaux & Seminara. Finally, we have shown that depth-averaged (Saint-Venant) equations are not able to reproduce the instability.

Climate and anthropogenic changes impact the conditions of erosion and sediment transport in rivers. Rainfall variability and, in many places, the increase of rainfall intensity have a direct impact on rainfall erosivity. Increasing changes in demography have led to the acceleration of land cover changes in natural areas, as well as in cultivated areas, and, sometimes, in degraded areas and desertified landscapes. These anthropogenized landscapes are more sensitive to erosion. On the other hand, the increase in the number of dams in watersheds traps a great portion of sediment fluxes, which do not reach the sea in the same amount, nor at the same quality, with consequences on coastal geomorphodynamics. This book is dedicated to studies on sediment fluxes from continental areas to coastal areas, as well as observation, modeling, and impact analysis at different scales from watershed slopes to the outputs of large river basins. This book is concentrated on a number of keywords: “erosion” and “sediment transport”, “model” and “practice”, and “change”. The keywords are briefly discussed with respect to the relevant literature. The contributions in this book address observations and models based on laboratory and field data, allowing researchers to make use of such resources in practice under changing conditions.

Introduction to Geophysical Fluid Dynamics provides an introductory-level exploration of geophysical fluid dynamics (GFD), the principles governing air and water flows on large terrestrial scales. Physical principles are illustrated with the aid of the simplest existing models, and the computer methods are shown in juxtaposition with the equations to which they apply. It explores contemporary topics of climate dynamics and equatorial dynamics, including the Greenhouse Effect, global warming, and the El Nino Southern Oscillation. Combines both physical and numerical aspects of geophysical fluid dynamics into a single affordable volume Explores contemporary topics such as the Greenhouse Effect, global warming and the El Nino Southern Oscillation Biographical and historical notes at the ends of chapters trace the intellectual development of the field Recipient of the 2010 Wernaers Prize, awarded each year by the National Fund for Scientific Research of Belgium (FNR-FNRS)

This book systematizes the concepts of contemporary coastal zone management and suggests possible structural and non-structural management tools for decision-making processes. Some successful adaptation measures and case studies on oceanic processes and coastal protection are discussed. High-frequency communications in coastal and marine environments are also addressed.All chapters contribute relevant information and useful content to scientists and other readers interested or concerned about the lack of adequate management actions and the installation of appropriate protections or their ineffectiveness in containing coastal vulnerabilities and risks.