Groundwater flow and transport model of the Red River/Interlake area in Southern Manitoba

Abstract

A regional flow and solute transport model was constructed for two bedrock aquifers in Southern Manitoba. The "Carbonate Aquifer" is located in the fractured, more permeable region of the outcropping carbonate rocks and is used for rural domestic, industrial, irrigation and agricultural purposes. The "Sandstone Aquifer" is located within the interbedded sandstones and shales of the Winnipeg Formation and is utilized for rural domestic purposes. Transmissivity measurements were obtained for both aquifers from pump and specific capacity tests. It was determined that the transmissivity in m2/s followed a natural log normal distribution for both aquifers with a mean of -7.2 and -8.0 for the Carbonate and Sandstone Aquifers, respectively. The variograms were calculated using an estimator developed by Li and Lake (1994). Fractal nature was not evident in the variogram of either aquifer. Bayesian Updating was used to generate heterogeneous hydraulic conductivity fields. For the Carbonate Aquifer this field was successfully used to assign hydraulic conductivity, however due to lack of measurements the hydraulic conductivity for the Sandstone Aquifer was assigned through zonation. The resulting flow model had a RMS error of 7.49 m. The plot of computed versus observed equivalent freshwater heads showed significant correlation. Linear regression was conducted and the slope and intercept compared against the desired values of 1.0 and 0.0, respectively, using the t-test. For the transport model, the RMS error was 2.9 g/L, however the plot of computed versus observed concentrations had a slope significantly different than one. The model was used to evaluate several water resources engineering applications. The model runs examining sustainability showed that 1 g/L contour moved slightly northeast in the Carbonate Aquifer and only had slight movement in the Sandstone Aquifer.