| Buried valleys occur across Canada and may be incised into either bedrock of overlying surficial sediment and infilled by a broad range of sediment facies (e.g. Russell et al. 2004). Across the Canadian Prairies over 20 000 km of buried valleys have been identified (Russell et al., 2013) mostly incised into Cretaceous shales (Cummings et al., 2012). Buried valleys within the surficial succession, also known as inter till aquifers, are commonly recognized but rarely mapped. Three different styles of buried valleys have been identified (e.g. Pugin et al., 2014) and attributed to erosion and infill by fluvial, glaciofluvial and glacial processes in the preglacial and glacial period (Cummings et al., 2012; Atkinson et al., 2013; Pugin et al., 2014). Alpha valleys are regional bedrock valleys inferred to be preglacial. Beta valleys are deeper incised parts within alpha valleys that may subtend from unconformities within the till succession. Gamma valleys are inferred to be the youngest, the narrowest and to be incised into either bedrock or surfical sediment, and may subtend from unconformities within the surficial sediment. The thickness of the surficial sediment filling and burying buried valleys is up to 350 m (e.g. Cummings et al., 2012). Buried-valleys fills are comprised of sand, gravel, mud and diamicton (till). Numerous valleys contain permeable sand and (or) gravel at depth, and shallower stratigraphy is commonly mud-rich diamicton (till). The resulting heterogeneity may compartmentalize the aquifers and create localized flow systems (e.g. Shafer and Pusc, 1992). The hydraulic characteristics of buried valleys are variable and it is necessary to carefully assess the geological setting of individual buried valleys. The till-dominated sediment that covers the Prairies is a primary control on the hydrogeological characteristics of buried-valley aquifers. It limits recharge to these aquifers. In areas where several tens of metres of till overlie buried valleys, hydraulic head responses to precipitations tend to be muted or absent, and recovery of head following intense pumping can take years (e.g. Maathuis and van der Kamp, 2003; Van der kamp and Maathuis, 2002). Some buried valleys may operate as regional groundwater drains, with modern rivers commonly functioning as discharge zones. A number of buried valleys have been the focus of study, notably the Estevan in Southern Saskatchewan (Maathuis and van der Kamp, 2003), Spiritwood in Southern Manitoba (Pugin et al., 2014), and valleys in the Cold Lake area of Alberta (Atkinson et al., 2013).
The Spiritwood Aquifer system in particular demonstrates this heterogeneity in valley erosion and fills with several generations of valleys of different dimensions and orientations (Pugin et al., 2014). Many of the intermediate depth valleys form inter-till aquifers and provide possible hydraulic connections to deeper buried valleys. The hydraulic boundaries of buried valleys are variable and it is necessary to carefully assess the geological and hydrogeological setting of individual buried valley segments. The resulting heterogeneity may compartmentalize the aquifers and create localized flow systems (e.g. Shafer and Pusc, 1992).
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