ClimateChange Assessment Guide.pdf - University of Waterloo

E-14Guide for Assessment of Hydrological Effects of Climate Change in Ontario The procedures followed for the setup, calibration and validation of HSP-F for Subwatershed 19 have been fullydocumented (EBNFLO Environmental, 2009). These steps were completed for Phase Two of the Subwatershed 19Study, undertaken from 2008 to 2009. That study has a broad scope and in addition to hydrologic modelling, includeswater quality modelling and assessment of several future scenarios with alternative land use and water managementscenarios. Climate change impact assessment has not been previously conducted in this area. The documentationrelating to streamflow model setup and testing provided with that study is summarized below.In model setup, the subwatershed is represented as a mosaic of urban and rural land elements. Each element hashomogeneous characteristics. Several elements together form catchments (i.e., discrete sewersheds and smalltributary catchments that combine to make up the subwatershed). Surface runoff is routed from each element into thelocal watercourse stream/sewer. Subsurface runoff (i.e., interflow and groundwater flow) is generally routed to thenearest local stream channel; however in some cases subsurface flows are routed to adjacent or downstreamreaches to reflect the general groundwater movement patterns observed in the study area. The watercourse reachmay represent a section of a tributary to the main channel, a pond or a section of the main channel of the Credit River.Each land element is characterized by its land use, quaternary geology and topography. These characteristics arereflected in the setup and parameterization of the model. Urban areas are characterized to reflect several potentialconnectivity schemes (i.e., the manner in which pervious and impervious surfaces are connected to each other and tothe local infrastructure) and land use types. Rural areas are assumed to have no significant imperviousness.Subwatershed catchments (Figure 1-4) were delineated by CVC to a much higher level of detail than in previousmodelling studies, as required for the DWSP Tier Three Risk Assessment. Currently there are 36 catchments,whereas 4 had been used in previous models (Credit Valley Conservation and EBNFLO Environmental, 2008).Catchments 1905 and 1907 have been further divided into upstream and downstream portions for this study, raisingthe total number of catchments in the subwatershed to 38. The subwatershed study report provides a table listing thecatchments, their drainage areas (ranging from 3.1 to 752 hectares) and identifies the local stream reach. Theaverage catchment size is about 155 hectares. The model is setup to produce and store streamflow output at thedownstream limit of all catchments.Land use cover is generally the most likely surface characteristic to be affected by human activities. The population ofthe Town of Orangeville and the urban footprint is expected to significantly change in the subwatershed as the Townof Orangeville is built-out to its limits (AquaResource Inc., 2008).For the purposes of developing model input, the aggregated land uses were designated as either urban or rural. Thisstep is critical as urban and rural lands are treated differently in modelling. All urban land use classifications weresorted and lumped into ten major land use designations while the rural land uses were sorted and lumped into ninemajor land use designations. In these land use designations all local roads were included with the prevalent land usein each area. In this way all roads are accounted for and their imperviousness is incorporated into that of the adjacentland use type.