DEVELOPMENT OF PROTOCOLS FOR 3D GEOLOGICAL MODELLING IN SUPPORT OF REGIONAL GROUNDWATER APPLICATIONS IN THE WINNIPEG/LAKE WINNIPEG REGION, CANADA

In the region around the City of Winnipeg, groundwater is obtained from bedrock aquifers. Fresh water in these aquifers consists of modern recharge and relict subglacial recharge, but usage is constrained by a saline water system recharged in South Dakota and Montana that discharges to the western Red River valley. Research on the long-term sustainability of this fresh groundwater resource is addressing protection of recharge, and ensuring that excessive pumping does not lead to unacceptable lateral migration of the saline waters. Modelling is a key element of this strategy, and a 3D geological model for the area was required. The model was built using a Province of Manitoba digital elevation model, Canadian Hydrographic Service bathymetric charts for the large lakes, surficial geological maps, drillhole and seismic information for the Quaternary succession, and Province of Manitoba models for the Phanerozoic rock units. For the Quaternary, key inputs to the 3D model of the sediments were cored holes logged by geologists, and geophysical surveys. These high-quality results were extrapolated laterally using water well data from 80,000 sites. Much effort was required to parse the 75,000 unique lithological descriptions in this database, and the results were interpreted using a scatterplot approach. The 200 km x 230 km study area was divided into 46 strips each 5 km wide, and a large colour chart was printed for each strip, showing all drillhole data, surficial geology, and surface elevation. The drillhole data, colour-coded for lithology, were interpreted as a series of vertical maps, using the same methods that are used to compile plan-view maps. The interpretation was captured as profiles at 5 km spacing, and gridded as 3D surfaces. This project has emphasized the need to develop protocols regarding data integration and error analysis in 3D geological mapping. The development of data models and decisions on appropriate data usage are required to link disparate datasets such as DEMs, bathymetry, plan-view geological mapping, cored and water well holes, and geophysical and hydrological data, in a GIS environment.