Quaternary Sequence Grid-based Hydrostratigraphic 3d Modelling by the Relative Method, Chteauguay River Watershed, Quebec

A grid-oriented technique has been developed in order to build a 3D hydrostratigraphic model of the Quaternary sediments overlying a regional fractured rock aquifer, in the area of Châteauguay located south of Montreal, Quebec, Canada. It is part of the St-Lawrence Lowlands, a topographical lowland underlied by Paleozoic sedimentary rocks. It is based on the integration of the surficial sediments map and borehole logs with the use of GIS and grid-calculator software (such as Mapinfo and Vertical Mapper). The applied methodology focused on the estimation of the thickness of the stratigraphic units rather than of the elevation of the contacts. First, a regular grid was generated over the study area with 30x30 m cells. The bulk thickness of the Quaternary sequence for each grid cell was computed as the difference between the terrain digital elevation model and the rock surface krigged over more than 5000 drillers’ logs available. A new computation method for the estimation of the discrete thicknesses is presented: the relative method in which the thickness is computed as a fraction of the bulk thickness. A more detailed perspective on this new 3D modelling technique is presented will be presented in Tremblay et al. (in prep.).