No abstract

Generalized Reciprocal Method (GRM) refraction surveys in glacial terrains frequently encounter complex geologic and hydrogeologic conditions. The complexity frequently centres around the shallow water table and low velocity of the unsaturated zone. Inaccurate determination of the velocity and thickness of this low velocity layer can have a significant effect on the depth estimate of lower layers. This paper discusses methods to optimize field data collection and processing to ensure proper analysis in these situations. A general rule of GRM surveys is that the geophone spacing should be less than one third of the XY distance of the shallowest layer. Since the XY of a shallow water table layer is often less than 2 metres, geophone spacings of less than 1 metre may be necessary. These spacings are frequently not cost effective, and alternative approaches may be required. Alternatives include; 1. using the GRM average velocity method and an estimate of the XY based on modelling, 2. combining the upper two layers, and 3. using time intercept methods to interpret short spreads collected at various points along the line. The sensitivity of the GRM is evaluated using a simple model. Random pick errors are introduced into the model, and the merit of arrival averaging is studied. Similarly, layer velocity errors, XY analysis errors and hidden layer problems are reviewed. Practical suggestions for GRM surveys in glacial terrains are offered. An approach for performing cost effective GRM surveys is presented. The approach is based on high redundancy data collection (multiple mid shots) for water table velocity analysis and duplicate arrival averaging. Finally, the importance of XY analysis for detecting hidden layers and bedrock surface features is discussed.

Low impact development (LID) strategies have received attention in recent years as offering a potential way to mitigate the adverse effects of urbanization on hydrologic flow and water quality. The obvious benefits of reduced peak flows and the sizing of storm water ponds can be simulated in models such as USEPA's SWMM; however, the analysis of LID system interaction with the groundwater system is challenging. Addressing questions related to local infiltration capacity, feedback from the groundwater system (i.e. rejected recharge and saturation-excess runoff), and ecological benefits, including the preservation of baseflow and wetland hydroperiod, requires a spatially distributed and integrated analysis of the hydrologic system. The purpose of this chapter is to illustrate the challenges and insights that the authors have encountered while simulating and comparing the effectiveness and ecological benefits of different LID scenarios using an integrated groundwater and surface water model. Additional discussion addresses how this approach can be used to complement storm water modeling and provide for a complete analysis of LID functionality.

Since about 2000, Ontario's municipalities, conservation authorities, provincial ministries and consulting firms have been variously engaged in preparing technically sophisticated numerical models for the purposes of managing and protecting water supplies. Not only have these models led to an improved understanding of water quantity and water movement within the province's watersheds, but the work has also led to a comprehensive synthesis of water related information across much of the province. A resultant ongoing challenge for all parties is one of maintaining this new knowledge based infrastructure for future use. The challenge is a difficult one, in light both of the limited finances, as well as the limited technical modelling expertise available within the province. However to not make use and build upon the important work that has been undertaken, would be a disservice to Ontario's citizens. It is therefore incumbent on the community of practitioners to figure out a strategic path forward. The goal of this half-day session will be to initially shed light on the ability of numerical models to provide insights into flow system behaviour and thereby be a valuable tool for water resources management. The follow up panel discussion will touch upon various issues related to broadening the use of numerical models. One specific topic of interest will be model management, this being a very new endeavour, having only recently arrived at Ontario's doorstep in a significant way following on the extensive technical work undertaken through Source Water Protection. Through the construction and use of numerical models, consultants assemble a tremendous understanding of the how water moves in the subsurface and how it interacts with the surface water environment. The entirety of this understanding can never be fully conveyed in a summary report. Drawing upon their considerable expertise in the construction and use of numerical models, the speakers will highlight various instances where numerical models have been used, or could be used, to reveal flow system behaviours that can assist Ontario to improve water management related decisions. Following upon the talks, stick around after the break for an engaging and insightful panel discussion that will address a broad range of current issues surrounding the use of numerical models in water management decision-making. Can any numerical model be re-used/re-purposed for future decision-making given that it has been built for a specific purpose? Should models be considered out dated and obsolete once they have served their initial purpose? What are the limitations to such re-use and how should they be conveyed? Is it that only certain elements of a numerical model be used into the future? Who should ensure models are up-to-date and reflect the most current understanding prior to their re-use? How can high level technical and policy managers be made aware of the considerable insights that numerical models can bring to bear on water management decisions? As a community of technical practitioners, is there a need to train colleagues and staff at provincial ministries, municipalities, conservation authorities and consulting firms, to be more comfortable with the insights and analyses offered up through numerical modeling? How is this best achieved? Will this lead to increased use of numerical models as a key input to guide decision making? Is there perhaps a role for a structured peer review system whereby credible modelling experts are retained to assist in model re-use/re-purposing?

One of the significant benefits of the tiered Ontario Source Water Protection water budget approach was the opportunity for significant improvement in numerical model analysis at each progressive level. The concurrent improvements in water use data, advances in computing and storage, and the release of a practical, open-source integrated surface water/groundwater model in 2008 (USGS GSFLOW) further supported the technical advancements. Most important, however, was the recognition that a holistic "one water" approach, addressing the entire hydrologic cycle, was necessary to address the cumulative effects of increased water use, drought, storage, and land use change on groundwater levels, streamflow, and wetland viability. Recognizing this challenge and opportunity, Earthfx strongly advocated conducting fully-integrated surface water and groundwater modelling studies for all the Tier 3 studies. A number of common response patterns and insights emerged from the six fully integrated Tier 3 and Lake Simcoe Protection models that we created. First, we found that groundwater feedback (Dunnian rejected recharge) was the dominant form of interaction, occurring in as much as 30 percent of the watershed areas. Hortonian runoff was found to be relatively rare, due to the infrequency of intense storms, summer ET deficits, and actively-vegetated loose soil conditions. Fully represented headwater streams and springs, high resolution surface topography, and detailed land cover were needed to represent spatially variable and often highly-focussed recharge. The need for detail extended into the conceptualization of the shallow subsurface, where detailed representations of the soil zone and shallow geology were needed to properly simulate subsurface stormflow and seasonal flow through highly permeable shallow aquifer units (weathered tills, epi-karst, etc.). Detailed representations of reservoir operations, quarry dewatering, irrigation water takings, and return flow were also found to be important to simulate overall watershed functions and, ultimately, producing a defensible risk assessment. Based on this experience and insight gained, we are convinced that the key to successful integrated modelling is in the details. Perhaps the most significant conclusion is that practical, engineering-scale integrated analysis can be accomplished within a watershed context. At too large a scale, many of the key process details and complex shallow system interactions would be oversimplified and generalized. Similarly, at too small a scale, such as limiting the model to the extended area of influence of a wellfield, would require oversimplification of model boundaries and neglect of the transient nature of surface and groundwater flow in the surrounding area. In 2010, Refsgaard et al. predicted that by 2020 all modelling in Denmark would consist of fully integrated analysis. Perhaps, due to the challenges and opportunities of the Tier 3 process, that future has arrived early in Ontario.