Application of geochemical and groundwater data to predict sinkhole formation in a gypsum formation in Manitoba, Canada

Numerical modelling approaches were used to investigate coupled groundwater flow and reactive transport processes in gypsum karst sub-terrain. A regional equipotential map and steady-state flow model were created using scarce data to gain insights into flow patterns and identify potential areas at risk for cavity and sinkhole development in a shallow gypsum formation. Coupled flow and reactive transport modelling was used to simulate the dissolution of gypsum between a sinkhole in a man-made drainage ditch and a quarry, where freshwater enters the drainage ditch and flows toward the quarry. Field data from a tracer test were used to characterize flow in the study area. The resulting regional equipotential map was valuable in identifying potential areas of sinkhole development; sinkholes occurred in areas underlain by thick gypsum formations with high flow gradients and radial flow. The reactive transport model was valuable in identifying the growth of the cavity and the timeline for the potential risk to road infrastructure. The reactive transport model indicated that cavity growth could be slowed by removing the inflow of freshwater into the drainage ditch. Groundwater equipotential maps, flow models and reactive transport models are valuable tools for the investigation of sub-terrain karst development including cavity development and sinkhole formation in evaporite minerals.