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.

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.

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.

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.

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.

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.