Modeling Water Quality in Southern Saskatchewan Watersheds
The presence of accumulated nutrients in surface waters is a great concern for water quality. In Saskatchewan, for many streams, data on water quality is limited both spatially and temporally. An eco-hydrological model is a relatively low-cost method to help assess water quality where there are limited measurements. The study area is located in the Canadian prairie region where potholes are the dominant landscape feature and farming is an extensive activity. Potholes are closed-surface depressions that have a significant role in the prairie hydrologic cycle, flood mitigation, and water quality. The current modelling study was conducted in three southern Saskatchewan watersheds: Pipestone Creek above Moosomin Lake, Swift Current Creek below Rock Creek, and Lightning Creek near Carnduff. The hydrological model SWAT (the Soil and Water Assessment Tool) with the Probability Distributed Landscape Depressions module (SWAT-PDLD) (with seasonally variable soil erodibility) used in simulating flow and water quality results were compared to SWAT with its in-built pond routine (SWAT-lumped). Model results were then used to determine pond spilling and non-spilling period to examine whether any relationships between observed nutrient loading and streamflow differed during spilling and non-spilling periods. Both the SWAT-PDLD and SWAT-lumped models showed “good” performance for calibration period and “satisfactory” performance for validation period respectively for streamflow simulation based on statistical metrics for Pipestone Creek and Lightning Creek watershed. However, the SWAT-PDLD performed “good” for sediment export, total phosphorus export and total nitrogen export simulation whereas the SWAT-lumped model performed “satisfactory” for the same cases. Simulation results were improved using SWAT-PDLD over SWAT-lumped model. Spilling and non-spilling events were identified and categorized based on pond outflow contribution to streamflow. Both models could not satisfactorily simulate the streamflow for the Swift Current Creek watershed. It has been noticed that the observed total nitrogen load was significantly higher during model-predicted spilling periods than non-spilling periods in the Lightning Creek watershed. However, observed sediment export and total phosphorus export did not appear any different between spilling and non-spilling events. In the Pipestone Creek watershed, the relationship between loadings and streamflow did not appear to be different during spilling and non-spillling periods for sediment export, nitrogen, and phosphorus.
Water Quality, SWAT-PDLD, Spilling.
Master of Science (M.Sc.)
Civil and Geological Engineering