Research Summary: Characterizing shallow groundwater systems

​Hokanson KJ, Mendoza CA, Devito KJ. 2019. Interactions between regional climate, surficial geology, and topography: Characterizing shallow groundwater systems in subhumid, low-relief landscapes. Water Resources Research, 55(1): 284-297. DOI: 10.1029/2018WR023934. 

Kelly Hokanson, PhD Candidate, University of Alberta

Carl Mendoza, University of Alberta

Kevin Devito, Platform lead, Theme 1: Boreal Plains, University of Alberta

Summary​
In this research we provide the first comprehensive characterization and synthesis of groundwater movement and water table behaviour in the Boreal Plains region of Canada. Topography is often used as a first order control over groundwater movement, however we show that in the low-relief, sub-humid Boreal Plains, topography is not a good predictor of water table position, and therefore groundwater flow patterns. 

We offer a discretization approach (i.e., categorizing or classifying) as an alternative to the traditional surface topography based approach of establishing watershed boundaries. Instead, we use hydrogeological response areas (HRAs), which are defined by substrate characteristics. 

​Results
Our findings show that the use of HRAs to evaluate hydrogeological characteristics of typical glacial landforms provides a convenient and holistic way of discretizing the landscape into unique sub-units defined by hydrogeological properties and water table conditions. By examining the magnitude and frequency of water table fluctuation, vertical hydraulic gradients, geochemical signatures, and stable water isotope ratios over 19 years, we demonstrate that groundwater is controlled by a hierarchy of climate, geology, and topography.

Application
HRAs are used to delineate chemoscapes and isoscapes (spatial distributions of geochemical and isotopic compositions of groundwater and surfacewater) to provide practical pre-disturbance hydrogeological benchmarks for developing land management practices. The results of this study provide managers and stakeholders with an understanding of the dominant controls on hydrological processes and indicates the value of focusing at an intermediate scale between the basin and the hillslope scale. We demonstrate that managers should consider the complex interactions of topography, recharge, and texture when planning and managing disturbed lanscapes because they are more spatially and temporally variable than previously thought.

Key Messages

• In sub-humid, low-relief landscapes, topography alone is inadequate to explain water table behaviour, groundwater geochemistry, and groundwater-surface water interactions through time or space.
  
• Instead of using topography to delineate regions (as in watershed delineation), hydrologic response areas (HRAs) are delineated using a hierarchical framework that considers climate information first, followed by geology, and finally topography.
  
• HRAs are shown to be an effective management unit for complex, low-relief, sub-humid regions and help explain the spatial variability of groundwater scale of flow, and regional variations in groundwater and surface water quality. 

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