In 1997, after the devastating Assiniboine River flood of 1995, a research effort was started to better understand and model Canadian Prairie hydrology with an emphasis on snowmelt derived flooding and the role of depressional storage in controlling the contribution of basin runoff to streamflow. This effort led to a hydrological model suitable for prairie applications including the impact of wetland drainage and restoration.
Centre for Hydrology Report No. 14, Improving and Testing the Prairie Hydrological Model at Smith Creek Research Basin has now been published, describing the results a multi-year study to better simulate the hydrology of a Saskatchewan prairie watershed with the Cold Regions Hydrological Model and then use the model to evaluate the hydrological function of depressional storage in the Canadian Prairies.
The main findings of the report are:
- A long-term measurement and computer modelling study by the U of S Centre for Hydrology has revealed that drainage of depressional storage is a major factor in increasing prairie streamflows in most years and increasing flooding in wet years.
- The basin of Smith Creek, SK, southeast of Yorkton has undergone substantial drainage. In 1958 there were 96 km² of wetlands (24% of thebasin area) and now there are 43 km² (11% of the basin area).
- The Prairie Hydrological Model was set up for Smith Creek and run over six years using good weather data from a U of S weather station – these years included the largest flood on record for the region, in 2011. The model was manipulated to decrease wetland volume (drainage) or increase wetland volume (restoration). The limit for restoration was the measured wetland extent in 1958, the limit for drainage was complete wetland removal from the basin.
- Wetland drainage has a very strong impact on streamflow in flood conditions. For the Flood of 2011, complete drainage of the existing wetlands would increase the 2011 flood peak by 78% and the 2011 yearly volume of streamflow by 32%.
- Wetland restoration has a strong impact on streamflow in flood conditions. For the Flood of 2011, restoration of wetlands from the current extent back to the extent measured in 1958 would decrease the 2011 flood peak by 32% and the 2011 yearly volume of streamflow by 29%.
- Drainage has an even stronger impact on streamflow in normal to dry years. For these years, streamflow volumes would increase by from 200% to 300% with drainage of current wetlands and the yearly peak flow would increase by from 150% to 350%.
- Over six years of computer model simulation (2007-2013), total streamflow volumes increased by 55% with complete drainage of existing wetlands and decreased by 26% with restoration of existing wetlands to their state in 1958.