Osmosis in groundwater

Abstract

In problems of groundwater flow and solute transport in clayey soils subject to salt concentration gradients, chemical and electro-osmosis can be too important to disregard, as is commonly done in geohydrology. In this thesis, we consider the quantification of these couple effects to be able to simulate experiments and natural situations involving possible chemically and electrically driven water flow. Because clay can act as a semi-permeable membrane, groundwater flow in clay layers may be driven by osmosis. This can be mathematically accounted for by extending Darcys law with a term related to a salt concentration difference. Also, electrical potential differences may induce water flow, in which case we speak of electro-osmosis. In this work, the incorporation of these processes in existing groundwater models has been thoroughly investigated. The relevant processes and corresponding coefficients have been reviewed and we have suggested some improvements. The equations are used to model lab and field experiments and it is shown how to obtain numerical and analytical solutions for these equations. Some mathematical properties of the model equations are studied and some existing numerical codes for groundwater flow are extended with chemical and electro-osmosis. An important result is derived when membrane potential is coupled to chemical osmosis. It is shown how an experiment that is shorted can be modeled and how measurements of parameters such as permeability should be corrected for electrical effects.