Characterizing surface water-groundwater interactions in an urban environment can be challenging, runoff patterns can be complex as land use and permeability can vary not only spatially throughout the effective catchment area but also temporally as urbanization occurs. Recently extracted Environment Canada data have allowed the creation of an instantaneous stream flow dataset dating to the late 1960s for many Ontario gauge stations. Temporal changes to urban land area, permeability, land use, and road length were quantified for each watershed from aerial photography spanning the period of record at approximately 8 year intervals. This allows for the identified trends in event parameters to be correlated with the alteration of the catchment over time.

Milton, Ontario, the fastest growing community in Canada in 2011, relies on a Region of Halton wellfield located at the base of a re-entrant valley cut in the Niagara Escarpment. Other significant local features include a managed reservoir system, ski resort, rapid urbanization, and the 6th largest operating limestone quarry in Canada. To understand the local water budget and assess sustainability and drought sensitivity, a fully-integrated groundwater and surface water model was developed using the USGS GSFLOW model. The simulations indicate that the system behaviour changes dramatically with the spring freshet and resulting converging valley flow. The complexity of the system clearly demonstrates the benefits of the high resolution, fully-distributed, transient integrated GW/SW model.

Low-Impact Development (LID) strategies have recently received significant attention due to the requirement to reduce the adverse hydrologic and water quality effects of urbanization. Traditional surface water modelling tools are limited in their ability to simulate low flow conditions, changes in baseflow and groundwater supported wetlands. Examples presented in this paper illustrate how GSFLOW can be used to represent and assess various LID designs at both the cell and sub-cell level. Earthfx modifications to the sub-cell model processes allow representation of smaller scale features such as green roofs and the re-direction of water from impervious to pervious portions of the cell such as with a down-spout disconnection strategy. In summary, the GSFLOW analysis provided a quantitative approach to compare and demonstrate the ecological linkage and benefit of various LID strategies.