CONCEPTUAL MODELS AND NUMERICAL MODELING OF UNSATURATED FLOW AND TRANSPORT IN FRACTURED ROCKS

The formulations and numerical modeling of several conceptual models for unsaturated groundwater flow and solute transport in fractured rocks,such as fracture-network models,continuum models,effective continuum models,dual-porosity(single-permeability)models,dual-permeability models,and multiple interacting continua models are discussed in this paper.In a fractured rock-mass,unsaturated groundwater flow could occur either in the rock matrix only or in the fracture network only,or in both the rock matrix and the fractures.For the former situation,only a single continuum needs to be considered,whereas for the latter,interchange flow at matrixfracture interface has to be taken into account.Generally,fracture network constitutes the main channel of solute migration;however,if the seepage and diffusion of solute between the fractures and the rock matrix become an important transport mechanism,solute interchange at matrix-fracture interface needs to be considered.In order to model such groundwater and solute interchanges,one must decide the form and extent of matrix-fracture interac tions,which result in extra uncertainties in the conceptual models as opposed to single-continuum models.and make the numerical modeling more difficult.In practice,it is not easy,or even not possible at all,to discern the exact form of unsaturated seepage,selection of the conceptual models largely depends upon the modeling objective and the extent of data acquisition and understanding about the site.Any model will be affected by the uncertainties involved in the model and model parameters.Therefore,it is necessary to consider comparisons with other complementary models.