Field monitoring of physical processes in stormwater wet ponds and wetlands in Calgary Alberta

Stormwater wet ponds and wetlands are commonly used to control excess runoff in urban areas by temporarily storing surface runoff and then releasing it to the downstream storm sewer system at a controlled rate. They can also improve the water quality of stormwater runoff by removing sediments, nutrients and other pollutants before being discharged into receiving water bodies (e.g., rivers). As a result, there is an ongoing need to understand the complex physical, chemical and biological processes in stormwater facilities as a function of local weather conditions, hydrological conditions, and the design of each facility. A comprehensive 2-year field monitoring program is being undertaken to monitor two stormwater wet ponds and two stormwater wetlands in Calgary, Alberta. The field data will support the future application of computer models to investigate the physical and biogeochemical processes that govern suspended sediment transport and nutrient cycles in ponds/wetlands. Both the field monitoring data and computer modelling will be used to improve the design and operation guidelines of stormwater facilities. This paper presents preliminary results from the first year (2018) of the field monitoring program. The response of the four ponds/wetlands to atmospheric forcing has been examined. The occurrence of stratification and its impact on water quality are also discussed. Thermal stratification led to low DO in bottom waters and created vertical patterns of phytoplankton productivity. Photosynthesis and respiration also contribute to DO and pH fluctuations in stormwater ponds/ wetlands.