Thermal Benefits and Impacts of the Proposed Water Reclamation Centre Discharge on the East Holland River

The Innovative Wastewater Treatment Technologies alternative was confirmed as the Preferred Alternative for accommodating the growth forecasted to occur in the Upper York Sewage Solutions (UYSS) Service Area to 2031 in the Regional Municipality of York (York Region). The UYSS Individual Environmental Assessment (EA) Report is expected to be submitted to the Ontario Minister of the Environment for review and approval by late 2013. A key element was the influence of the treated clean water discharge from the proposed Water Reclamation Centre (WRC) on the East Holland River and its thermal régime. The purpose of the subject study, conducted as part of the EA, was to study potential thermal benefits and impacts of several locations for the WRC discharge on the East Holland River.

Two hydrodynamic models, Environmental Fluid Dynamics Code (EFDC) and CE-QUAL-W2 (W2 in short) were applied to evaluate the potential thermal benefits and impacts of the proposed alternative WRC discharge locations. River bathymetry was compiled in ArcGIS from various survey datasets. For the areas with no survey data, an interpolation algorithm was developed using VBA/ArcObject.

The EFDC grid was constructed by RGFGRID, a utility released with Delft3d Suite, which can generate a quadrilateral grid confined with splines. The generated grid was then imported into EFDC_Explorer (EE, a GUI for EFDC) for model setup. A python script was written to convert the EE exported plot file to polygon shapefile for GIS display. W2 model divides the study domain along lateral direction into segments, and in vertical direction into layers requiring the widths of each layer at every segment. A width interpolation algorithm was formulated in VBA/ArcObject from river shoreline boundary and a DEM covering the East Holland River to generate the widths for each layer. Typically W2 model segments have overlapping areas, causing difficulties in interpreting ice thickness in these areas. A GIS post-processor was therefore developed to convert segment polygons to vertices interpolated to raster for better ice thickness distribution display.

EFDC and W2 were built with the same external forcing variables except for using relative humidity for EFDC and dew point temperature for W2. The forcing variables were flow rates, water levels, CHI has been utilized for the study, which enables users to directly use radar generated rainfall datasets. The analyses applied radar-generated rainfall for historic local storm events, as well as the transposition of radar-generated data for formative storms from other areas of Southern Ontario. The results of this study have demonstrated that the application of radar rainfall data can improve calibration of a hydrologic model and can provide important insight into the performance of stormwater management infrastructure.