STREAM BED FACIES MAPPING TECHNIQUES APPLIED TO THE INVESTIGATION OF GROUNDWATER-SURFACE WATER INTERACTIONS IN GEORGETOWN, ONTARIO, CANADA

Understanding groundwater-surface water interactions are of great importance for communities who depend on potable groundwater. Georgetown, a community of ~40,000 in southern Ontario extracts potable water from aquifers within Quaternary-age sediments that supply the Cedarvale Well Field. The urbanized fluvial systems of Silver and Black creeks cross the Cedarvale Well Field and contribute to the recharge of the aquifers, although little is known about the precise nature of these groundwater surface-water interactions. This poster reports a study that integrates sedimentologic, topographic, and hydrologic data to create a map-based framework for analysis of groundwater surface-water interactions within this system.

A 400 m-long segment of Silver Creek that directly overlies the Cedarvale Well Field was selected for study. Detailed facies mapping of streambed sediments allowed the identification of six major facies types on the basis of sediment texture and inferred permeability characteristics. The deepest portions of the creek are armoured with boulder gravel containing clasts up to 75cm diameter. Shallower and marginal areas of the creek are characterized by gravels covered by varying amounts of mud and algae, coarse to fine grained sands, muds and organic sediments. Stream bed topography was recorded using a Hemisphere GPS – S320 unit and topographical data were subsequently modeled using ArcGIS to produce a digital elevation model (DEM) of the study area. Integration of the DEM with the facies map allowed the creation of a 3-D image of the creek bed and sediment distribution. This map serves as a framework for identification of significant features within the fluvial system, such as highly permeable gravel-floored pools and depressions that may function as sites of groundwater discharge and/or recharge. Hydrologic data recorded by gauging stations, mini piezometers, and shallow monitoring wells at several sites along the creek provide information about stream flow and shallow groundwater fluxes. Integration of these data with the facies map and DEM will allow identification of areas of potential water loss or gain along the studied portion of Silver Creek. Future work will utilize water temperature measurements to validate predictions made by this facies mapping study.