Stream Flow Simulation of a Canadian Prairie Watershed: Assessment of the Impact of Wetland Drainage and Climate Change on the Hydrology of the Pipestone Creek, Saskatchewan

Abstract

Within the scope of Watershed Evaluation of Beneficial Management Practices project in Saskatchewan, the Soil Water Assessment Tool model has been calibrated and validated at daily and monthly time steps for a watershed within the Prairie Pothole region of North America. The model uses the concepts of the hydrological equivalent wetland, limited weather data, and the gross and effective drainage areas introduced in the 1950s to simulate flows at one streamflow gauge in a 2,242 km2 watershed. The Sequential Uncertainty Fitting algorithm version 2 was used to calibrate and validate the model at daily and monthly time steps for the period 1997-2005 and 2005-2009, respectively. The model performs well capturing the magnitude and timing of the peaks during spring runoff. Annual volumes during the calibration period are well represented by the model at monthly time steps, although the performance of the model decreases during the validation period (2002-2005) which is represented by lower statistics. The successful calibration and validation of the model make possible the assessment of the impact of wetland drainage and climate change on the hydrology of the Pipestone Creek Watershed. The impact of wetland drainage on hydrology is evaluated by creating three different drainage scenarios which account for a drainage of 15% (Scenario 1), 30% (Scenario 2), and 50% (Scenario 3) of the non-contributing area. Results of these simulations suggest that drainage increases spring peak flows by 50%, 79%, and 113% for scenarios 1, 2, and 3, respectively, while annual flow volumes are increased by 43%, 68%, and 98% in each scenario. Years wetter than normal present an increase of peak flows and annual flow volumes of less than the average of the simulated period. Alternatively, summer peak flows present the smaller increase in terms of percentage during the simulated period. In addition, five Global Circulation Models (GCMs) and three climate change scenarios are used to drive the calibrated model and assess the impacts of climate change for the period 2031-2060. Overall, the models agree, estimating an earlier spring runoff, higher spring flow volumes and soil water content. Actual evapotranspiration is expected to increase during spring and decrease during fall, while there is little anticipated change in summer actual evapotranspiration rates. The projections of streamflow and soil water content are more uncertain during the summer and fall seasons due to the wider range of change forecasted.