Présentations Colloques

Oral Presentation
Session 8.03: Geometrical structure and hydrogeological properties of Hard-Rock aquifers.
Normani Stefano
Groundwater Divides in a Fractured Crystalline Rock Setting
The lateral extent of a groundwater model domain is normally chosen based on topography and surface water divides with groundwater divides assumed to be coincident with surface water divides. In fractured rock settings, fracture zones may cross watershed boundaries, and surface water divides, to permit groundwater flow between watersheds, where none would be assumed based solely on surface water divides. The interconnectivity of the permeable three-dimensional fracture zone network both within and across watersheds is an important pathway for the possible migration and subsequent reduction in groundwater and contaminant residence times. ****A high resolution three-dimensional sub-regional scale discretely fractured groundwater flow model was developed from a larger 5734 square kilometre regional-scale groundwater flow model of a Canadian Shield setting. The discrete fracture dual continuum computational model HydroGeoSphere was used for all simulations. A discrete fracture zone network model, generated using MoFrac and delineated from surface features, was superimposed onto an approximate 1.16 million element domain mesh with approximately 1.24 million nodes. Orthogonal fracture faces (between adjacent finite element grid blocks) were used to best represent the irregular discrete fracture zone network. The crystalline rock matrix between these structural discontinuities was assigned flow properties illustrative of those reported for the Canadian Shield for the shallow, intermediate, and deep groundwater systems.****Steady-state simulations are conducted with different characterizations of the three-dimensional fracture zone network, and surface boundary conditions for the groundwater system. Performance measures for the sensitivity analysis include freshwater heads, linear velocities, and mean life expectancy. The objective of the work is to determine the sensitivity of groundwater divides to the geometry and characterization of discrete fracture zone networks. This work clearly shows that discrete fracture zone networks that have significant length at divides can require modification of the spatial extent of the conceptual model.**