CONCEPTUAL, GEOLOGICAL AND NUMERICAL GROUNDWATER FLOW MODELS OF THE SPIRITWOOD BURIED VALLEY AQUIFER IN SOUTHWEST MANITOBA

The Geological Survey of Canada (GSC) has been studying the regional geology and hydrogeology of the Spiritwood buried valley aquifer in southwest Manitoba. The buried valley extends from Manitoba into and across North Dakota where it contributes large volumes of groundwater. In this region, there is limited access to moderate and high yield sources of groundwater from shale bedrock or inter-till aquifers. In contrast, buried valley aquifers offer the potential for larger water supplies provided there is adequate recharge.

In addition to using traditional characterization and mapping techniques (e.g., water well records and monitoring wells), the GSC has also been developing innovative approaches, such as seismic reflection and airborne time domain electromagnetic (TEM) surveys, to delineate the Spiritwood buried valley aquifer system. Results indicate that the Spiritwood buried valley in Manitoba is not a single valley feature. Instead, three different valley types were identified, each of differing dimensions, form, extent and depth, yet all are at least partially incised into bedrock. The conceptualization of the Spiritwood buried valley as a complex interconnected network of buried valleys has significant implications for the interpretation of groundwater flow.

A 3D numerical geological model of the regional flow system was developed, using Leapfrog Hydro™ geological modelling software. It was based on water well records, borehole coring, a digital elevation model and surficial geological maps. Within the TEM survey area (1000 km²), inverted conductivity results and seismic profiles provided higher spatial resolution geophysical data compared to sparse borehole records alone. These data were particularly important for delineating the extent of the shallowest buried valleys that may provide hydraulic connection to deeper buried aquifers. Guided by the conceptual and digital 3D geological models and supported with results from a baseflow survey, a 3D finite element groundwater flow model is being developed to assess groundwater flow patterns and fluxes. The innovation of collecting and integrating high resolution datasets into conceptual and numerical model development will refine mapping and assessment of buried valley aquifers. © Her Majesty the Queen in right of Canada 2013.