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.
IAH Talk EJ
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.
Estimating groundwater recharge is a significant aspect of the water budget model development and calibration process. The capability of GSFLOW to represent surficial processes on a higher resolution grid than the ground water system allows the detailed representation of topographic features such as hummocky topography, swales, and the geologic features that are evident in high resolution DEMs. This spatial relationship is found in Southern Ontario where till uplands are frequently adjacent to beach deposits or permeable tunnel channel sediments. In summary, recent simulations suggest that groundwater recharge should not be thought of as a one dimensional vertical process, but as a complex three dimensional process where topographical and spatial material relationships are significant factors.
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.
Engineering and water management challenges increasingly require integrated surface water and groundwater assessment. Three examples of GSFLOW solutions are presented. A detailed assessment of the interaction between proposed stormwater ponds and existing wetlands in a permeable South Florida aquifer system allows integrated assessment of dry-season hydroperiod preservation and wet-season storm runoff. A multiwatershed-scale water budget simulation of municipal wells and hundreds of competing agricultural, private and large golf course takings demonstrates that detailed assessment of snow melt and 3-dimensional runoff and infiltration in hummocky terrain is essential to the water budget assessment and drought analysis. A third example shows how GSFLOW was used for comparative analysis of low-impact urban designs scenarios (LIDS) that were undertaken to preserve recharge, optimize land use and protect the natural heritage system and groundwater levels in a new proposed community.