SIMULATING COMPLEX FLOW AND CONTAMINANT TRANSPORT DYNAMICS IN AN INTEGRATED SURFACE-SUBSURFACE MODELLING FRAMEWORK

Over the past several years, increasing attention has been directed towards understanding flow and contaminant transport exchange processes occurring at the interface between surface water and groundwater, particularly in the vicinity of riparian zones in riverine valleys and within the hyporheic zone. In this paper, we will examine these processes in the context of the control-volume finite element model, HydroGeoSphere, a fully-integrated 3D surface/subsurface model. HydroGeoSphere can simulate water flow and advective-dispersive solute and heat transport over the 2D land surface and in the 3D subsurface under variably-saturated conditions. Recent additions to the model include a dual-porosity, dual-permeability formulation for application to media containing macropores and fractures, dynamic evapotranspiration and snowmelt processes and reactive solute transport. A number of applications of the model to catchments of various scales, ranging from the scale of an intensively-monitored rainfall-runoff-tracer experiment (~ 2000 m2), to a regional-scale basin of about 8000 km2, to the continental scale comprising the entire Canadian land mass illustrates the complexity of watershed dynamics. The model capabilities and its main features will be demonstrated here with several high-resolution 3D numerical simulations to examine near-surface and deep-seated water cycling, groundwater-surface water interactions, recharge-discharge patterns and solute mixing processes over various spatial and temporal scales. The simulations stress the advantage of using a process-based model such as HydroGeoSphere for the prediction of the impacts of alternative water and land use management scenarios, but also point to the intense data needs for routine application of integrated surface/subsurface models.