Modeling the Streamflow Sensitivity to Wetland Drainage and Restoration Over the Canadian Prairies Using a Basin Classification Approach

The effects of wetland management of drainage and restoration on the hydrology of small basins over the Canadian Prairies, were investigated using a virtual basin modelling approach created through the Cold Regions Hydrological Modelling platform (CRHM) for seven biophysical basin classes that typify the region. The model included wind redistribution of snow, energy balance snowmelt, infiltration to frozen soils, Penman-Monteith actual evapotranspiration, soil and ground water dynamics and fill and spill of internally drained surface depressions that often form wetlands. Wetland loss induced by agricultural drainage was represented by scenarios that progressively reduced the depression area and storage capacity by increments of 10%, and ongoing wetland restoration policies were represented by expanding the existing depressions to historical sizes. Model simulations showed that, on average, both annual total streamflow and maximum daily streamflow had the largest sensitivities to wetland drainage in the pothole pond dominated basins. Every 10% loss of depression area resulted in a 15-22% increase in annual streamflow volume and a 13-18% increase in maximum daily streamflow from the pothole-dominated basins, whilst those increases were only 3-9% in other basin classes. Every 10% gain in depression area by restoration resulted in a 7% decrease in maximum daily streamflow from the pothole till basins, contrasted by a 0.2% decrease from the high elevation grasslands basins. Wetlands restoration represented by a 40% increase in depressional area, close to the historical maximum as indicated in the pothole till basins, reduced annual streamflow volume and peak daily streamflow by 5-36% and 1-28%, respectively, over the Prairies. Wetland restoration strategies of from large to small depressions and from bottom to top of the basin exerted a small influence on annual streamflow volume sensitivity, whilst restoring the wetlands closer to the basin outlet tended to be more effective in attenuating the maximum daily streamflow.