Mathematical Modeling of the Suspended Sediment Dynamics in the Riverbeds and Valleys of Lithuanian Rivers and Their Deltas.

Water pollution is a major global problem that requires ongoing evaluation and revision of water resource policy at all levels (from international down to individual aquifers and wells). It has been suggested that it is the leading worldwide cause of deaths and diseases, and that it accounts for the deaths of more than 14,000 people daily. In addition to the acute problems of water pollution in developing countries, industrialized countries continue to struggle with pollution problems as well. Water is typically referred to as polluted when it is impaired by anthropogenic contaminants and either does not support a human use, such as drinking water, and/or undergoes a marked shift in its ability to support its constituent biotic communities, such as fish. Natural phenomena such as volcanoes, algae blooms, storms, and earthquakes also cause major changes in water quality and the ecological status of water. Most water pollutants are eventually carried by rivers into the oceans.

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

The vertical distribution of suspended sediment concentration and velocity plays a major role in the study of the transport rate and the transport capacities of a river. Many suspended sediments concentration and velocity profiles exist in the literature, having ambiguous conditions of application. In addition, it is not easy to conduct in - situ measurements. This reveals, not only the utility of using numerical profiles, but also the responsibility of choosing an optimal one.The present thesis aims to conceive new tools for studying the vertical velocity and concentration distribution. In this context, we present two new sediment diffusivity coefficients obtained by the introduction of correction operator on the parabolic diffusivity coefficient. These models are implemented in the convection diffusion equation to generate two analytical concentration profiles and using the Boussinesq assumption, they lead to two analytical velocity profiles. Also, we conceive a method for choosing between different mathematical representation of a same physical phenomenon, and two methods for the intersection between these representations when more than one is applicable and for the extension of the representations to the cases where no model is applicable. We apply this method on the study of the vertical velocity profile and the sediment distribution in steady and uniform sediment laden open channel flows, and we develop the expert system for the vertical sediment concentration distribution code_ERESA.In an appendix, we test the use of the finite volume code_Saturne for the study of the vertical velocity distribution and suspended sediment concentration in open channel flows.