Integrated surface water/groundwater modelling is a preferred approach for watershed management studies. Particularly critical to the development of integrated models is the balanced use of fluxes and potentiometric heads (flows and levels). Our experience suggests that the key to the integrated analysis of flows and levels begins with the construction of an integrated relational database. Finally, our experience suggests the most common mistake made in the development of an integrated model is spending too much time refining the sub-models prior to integration. While it may be widely recognized that the quality of the model depends on the underlying data, without an integrated approach even good data can be wasted.
The MacKay River Watershed, northwest of Fort McMurray, Alberta, Canada, is a diverse oil sands development region with numerous steam-assisted gravity drainage (SAGD) operations planned or in production. Earthfx developed an integrated surface water/groundwater model using the USGS GSFLOW code to assess the cumulative impacts of SAGD operations on the MacKay watershed. Multiple scenarios representing groundwater diversions and land alteration under pre-development, current and future development conditions were simulated on a daily basis over a representative 25-year climate period. The analysis indicated that projected water use in the study area is broadly sustainable on a watershed scale; however, ongoing efforts will be needed to mitigate effects.
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. Recognizing this challenge and opportunity, Earthfx strongly advocated to conducting fully-integrated surface water and groundwater modelling studies for all the Tier 3 studies. Perhaps the most significant conclusion is that practical, engineering-scale integrated analysis can be accomplished within a watershed context. 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.
Mining of sand and gravel from below the water table typically involves removal of cover material and exposing the groundwater (in the form of a flooded pit or pond) to direct insolation. Earthfx developed a groundwater flow and heat transport model to assess potential off-site thermal migration at an aggregate operation in southern Ontario, Canada. Extraction of sand and gravel was underway when a thermal plume emanating from the on-site pond was identified, potentially impacting a nearby trout hatchery. This study illustrated how MODFLOW-NWT in conjunction with PRMS and the updated MT3D-USGS code can be used to successfully characterize the thermal regime surrounding sand and gravel operations, and evaluate potential impacts from thermal plume migration on nearby ecological receptors.
Long-term monitoring (LTM) networks, particularly in northern or remote locations such as the Alberta Oil Sands, are expensive to build and maintain. The need to characterize, understand and monitor cumulative effects in these watersheds remains high. Our recent experience demonstrates that the comprehensive approach inherent in the development of an integrated surface water and groundwater model can provide significant insight into the design and optimization of a LTM network. Examples from multiple integrated modelling projects demonstrate the benefits of a model-driven LTM network design. Finally, Earthfx is using Business Intelligence (BI) database concepts to integrate and manage the complex database storage and analysis needs of an integrated monitoring and modelling strategy.
The assessment of mine or quarry development requires a multi-disciplinary approach to address the range of water-related concerns. The fundamental issue is that many of the effects of development, and pit inflows in particular, cannot be accurately separated into surface and groundwater components. Integrated surface water and groundwater models can address the complete hydrologic cycle in a manner that rigorously addresses the processes, spatial and temporal interactions. The benefits of this approach include a comprehensive assessment within an integrated framework. While sensitivity analysis is difficult due to long simulation times, the transient comparison provides unique insight into system behaviour.