ClimateChange Assessment Guide.pdf - University of Waterloo

Appendix E E-15Subwatershed 19 Case StudyMore than three quarters of the subwatershed has been designated as rural, with 42% of that area as agriculture.Forest, wetlands and open space constitutes most of the remaining rural area. Almost one quarter of thesubwatershed has been designated as urban, with the residential areas constituting 56% of the urban area.Commercial areas, highway corridors and parklands constitute the remainder. The existing land use scheme forSubwatershed 19 is shown in Figure 1-2.Beyond land-use, some of the most critical hydrologic modelling input parameters are related to soil characteristicswithin each catchment. Characteristics of soils in the upper topsoil, or vadose zone, affect the water balance at thesmallest scale, thus, profoundly affect overall water quality and hydrology. Soil characteristics relating to hydrologicbehaviour have been assigned based on quaternary geology. The source of this information and its processing forthis study are discussed in an earlier report (AquaResource, 2008).Four soil type classifications were employed in this model setup. The soil classifications correspond to soils with highinfiltration and water holding characteristics (i.e., sands and gravels), medium infiltration characteristics (i.e., finesands and silts), low infiltration characteristics (i.e., silts and clays) and organic soils with high water holdingcapabilities. For the purposes of identification, the four soil types are termed A, B, C and O, respectively;corresponding to their approximate hydrologic soil groupings (HSG), an agricultural classification system often used inmodelling.The subwatershed’s watercourse network represented in the HSP-F model consists of a set of reaches that representthe main stem of the Credit River, as well as selected portions of tributaries. In general, each catchment contains onereach. Inflow to the reach is from both local and upstream contributions.Representative stream and valley cross-sections for each reach were used to develop the necessary average depthsurfacearea-reach volume relationships (i.e., flow tables-FTABLES) for each reach. HEC-2 (U.S. Army Corps ofEngineers) input files provided by CVC were used to determine representative cross sections for all reaches.The stage-storage and stage-weir flow relationships for Island Lake were taken from GAWSER modelling (Schroeter& Associates, 2004). Operating permits issued by the Ontario Ministry of the Environment to CVC specify damoutflow rates on a monthly basis, as determined for flow augmentation downstream. CVC regulates outflow using amanually operated gate valve at the South Dam. A time series of requested outflows has been developed for this sitebased on the operating permit. No continuous long-term record of outflow rates is available to aid calibration, so themandated flows have been used as a starting point in calibration.Figure 3-1 includes a schematic of Subwatershed 19 modelled reaches and the drainage areas upstream of nodalpoints. Note that about 40% (i.e., 25 km 2 ) of the surface subwatershed area is upstream of Island Lake. Majortributaries include Upper and Lower Monora Creek in the northwest and Mill Creek in the southwest. Unnamedtributaries in the east side of the subwatershed also contribute significantly in terms of drainage areas.