DEVELOPMENT OF A NEW WATER QUALITY MODEL AND ITS USE IN DEFINING TOTAL LOADING MANAGEMENT TARGETS FOR THE CITY OF CALGARY

Nutrient inputs from the City of Calgary result in the growth of aquatic vegetation in the Bow River. The vegetation consists primarily of rooted aquatic plants (macrophyte), with lesser amounts of benthic algae (periphyton). Sufficient biomass is generally present during the open-water season to notably affect dissolved oxygen levels in the river. In 2002, the City of Calgary initiated a study to develop a total loading management plan that addresses inputs from the City of Calgary's storm sewers and wastewater treatment plants, with the goal of protecting aquatic life in the Bow River. To develop an effective total loading management plan, the linkage between nutrient loading, aquatic plant and algae biomass and their combined effect on dissolved oxygen levels in the river had to be explicit modelled. No readily-available water quality model included all of the components required to complete this task. A new computer simulation model was, therefore, developed.The new software package, entitled WASP-MG, was successfully combined with HEC-RAS to simulate conditions in the Bow River and produce total loading management targets for the City of Calgary. WASP-MG includes a macrophyte module that accounts for the effects of scour on the growth of aquatic plants and the ability of these organisms to access nutrients contained in both the water column and the underlying sediments. It can be effectively applied to riverine systems to assess how nutrient loading can affect the growth of aquatic vegetation and subsequently influence in-stream DO levels.