Integrated groundwater/surface water models are typically thought of as research tools, yet they can be applied in a practical manner to study impacts of land development and to assess the effectiveness of engineered mitigation measures. An integrated model was determined to be most appropriate tool for simulating groundwater and hydrologic response. There is considerable groundwater/surface water interaction across the site due to the shallow water-table and numerous streams and wetlands. To represent Natural Conditions, the calibrated model was modified by removing all anthropogenic features such as roads, ditches, berms and water control structures that affected drainage and overland flow. Model simulations predicted streamflow, wetland stage, and groundwater heads on a daily basis for the three scenarios.
Earthfx has developed multiple integrated surface water/groundwater models for assessing the watersheds that drain into Lake Simcoe, Ontario, Canada. The study areas feature competing water uses from municipal drinking water systems, industrial and agricultural takers, quarries, gravel pits, and navigation canals which were all represented in the models. These projects have demonstrated the value of undertaking detailed drought assessments at the watershed scale. The assessment of the study watersheds under a changed climate was conducted using a “change field” method. Integrated modelling exercises can help explain the linkages between the groundwater system and surface water features. This functional, hydrologic knowledge can provide the insight necessary to develop both drought and climate change adaptation strategies.
Integrated modelling has emerged as the preferred approach to address complex watershed management, cumulative impact and engineering scale problems such as mine development. Our experience, based on the construction of more than 10 integrated GSFLOW models, suggests that this approach is flawed in two key areas. The benefits of early integrated calibration, including calibration to total measured streamflow using measured precipitation, are clearly demonstrated by a GSFLOW simulation of the interconnection between a managed reservoir and a municipal wellfield. To conclude, early sub-model integration, flexibility and an open approach to shallow system re-conceptualization is the preferred approach for integrated model development.
MODFLOW Oro Climate Change Assessment
Earthfx developed several integrated surface water/ groundwater models for assessing watersheds that drain into Lake Simcoe, the fourth largest lake in Ontario. The GSFLOW model for the Oro Moraine area, located on the west shores of Lake Simcoe, was developed with a particular focus on the shallow groundwater flow system, headwater streams, and wetlands that form on the flanks of the Oro Moraine. The model was then used to simulate groundwater and stream flow under future climate conditions. Daily climate inputs for 1970-2000 were used to simulate baseline conditions. The GSFLOW modelling studies proved extremely useful for analyzing the interplay between the surface water and groundwater systems under a variety of climatic conditions. The studies demonstrated the usefulness of watershed-scale integrated models in assessing drought and climate-change sensitivity.
Strategies for Integrated Model Calibration
Integrated modelling has emerged as the preferred approach to address complex watershed management, cumulative impact and engineering-scale problems such as mine or quarry development. In a related initiative, the surface water community recently completed a 10 year effort to assess strategies and approaches for predictions in ungauged basins (PUB). Our experience, based on the construction of more than 10 integrated GSFLOW models, is consistent with these PUB recommendations and their emphasis on basin “form and function”. To conclude, we feel that integrated models are more than ready to provide the key insights into basin form and function that the PUB scientists have identified.
Assessing the cumulative impact of surface and groundwater diversions is central to water resource permitting and management. Where the diversions and impacts are limited to one domain, such as the groundwater system, general assessment measures such as cumulative drawdown can be clearly defined and evaluated. Our experience with Source Water Protection studies involving hundreds of diversions indicates that integrated models provide an assessment framework that reconciles these issues. Overall, an improved system understanding should be the first goal in assessing cumulative effects. Integrated modelling can provide the insights needed to support the informed application of provincial thresholds, while also providing a tool to define and assess local adaptive management monitoring targets for the longer term.
Extraction of granular material below the water table has the potential to disrupt nearby temperature-sensitive aquatic ecosystems through off-site thermal plume migration. Earthfx reviewed site conditions and constructed detailed 3-D stratigraphic and hydrostratigraphic models for the study area. Most significantly, the stratigraphic model mapped a buried till drumlin that strongly affected groundwater flow across the site. Groundwater velocities and seepage rates from streams and lakes were supplied to the thermal transport model (MT3DMS). By creating a regional understanding of the movement of groundwater and the thermal plume, the anthropogenic thermal plume could be characterized and ultimately differentiated from the ambient seasonal fluctuations.
Agricultural activities can place significant stress on local water resources; and water takings either through groundwater pumping or streamflow can produce water shortages and negatively impact aquatic ecosystems. The U.S. Geological Survey has developed an open-source integrated modelling code, GSFLOW, which combines the proven PRMS hydrologic model with the robust, modern MODFLOW-NWT groundwater model. Earthfx has further modified the code to simulate demand-driven irrigation based on dynamic soil moisture conditions. This extended version of GSFLOW has been tested in the Whitemans Creek watershed in southwestern Ontario. The model simulates groundwater heads, streamflow, and wetland stage on a daily basis under current conditions, along with future climate, drought and development scenarios. Results of the model will be utilized in the future to better manage water allocation under drought conditions.
Dynamic Irrigation Demand Module
Understanding the cumulative effects of pumping, irrigation, drought and groundwater/surface water interaction is central to the agricultural water management problem. The USGS GSFLOW code combines the PRMS hydrologic model with the MODFLOW-NWT groundwater model into a fully integrated model that is ideal for studying groundwater and surface water interaction under drought and climate change conditions. Earthfx has created a unified tool to address this challenge by modifying the GSFLOW code to incorporate the approaches and features of the Farm Process module. The model simulates groundwater heads, streamflow, and wetland stage on a daily basis under current conditions, along with future climate, drought and development scenarios. Results of the model will be utilized in the future to better manage water allocation under drought conditions.
The MacKay River Watershed, immediately northwest of Fort McMurray, AB, is a diverse oil sand development region with near-surface minable reserves and both shallow and deep SAGD targets extending under the Birch Mountain headwater area. In 2014, Earthfx Inc. was hired by the Cumulative Environmental Management Association (CEMA) to answer the question: “Is there enough water in the watershed to sustain a responsible level of development?” To address this question, Earthfx proposed an innovative, high resolution, fully-integrated surface water and groundwater modelling approach. The analysis indicates that projected water use in the study area is broadly sustainable on a watershed scale. Future applications including permit assessment, climate change, well optimization, monitoring network design and watershed evaluation and management.
EJ Wexler CMWR
Integrated modelling has emerged as a powerful tool to assess and understand the interactions between surface water and groundwater processes. Experience has shown that spatial scale is a critical factor when undertaking integrated studies. The models provided the most meaningful results when applied to watersheds or multiple subwatersheds. A second advantage of this new approach is that cumulative effects assessments can move beyond simple current and future condition “snapshot” comparisons. Practical problems such as model stability and long run times are still issues that must be addressed from the computational end. Integrated modelling represents the tool of choice for understanding and solving today’s complex water management challenges.