Linking spatial patterns of perched groundwater storage and stormflow generation processes in a headwater forested catchment

This study examined hydropedological patterns and storagedischarge relationships towards catchment process understanding at a small forested site, the Hermine (Laurentians, Quebec, Canada). The catchment is characterized by a steep surface topography and a shallow, irregular, low-permeability soil layer (LPSL), thus offering two possible main hydrologic drivers for runoff generation and routing. Using spatially detailed topographic data of the soil surface and the LPSL, water table levels measured at 94 locations on 50 occasions were expressed as 5 perched groundwater (PGW) storage variables: (i) a binary index illustrating the presence/absence of surface water, (ii) a soil saturation deficit, (iii) a water table elevation above the LPSL, (iv) a classification of sites as being in a dry, filling or spilling subsurface depression, and (v) a water table elevation above an underlying filled subsurface depression. The most common proxies for PGW storage, namely the saturation deficit and the location of surface saturated areas, were least appropriate to portray the Hermine catchment dynamics. Patterns of PGW storage were initially important during a rainstorm to trigger a response at the outlet but then remained unchanged even though streamflows continued to increase up to a higher order of magnitude. Hydraulically limited water tables were shown to exist in some areas, thus hinting towards the coexistence of rapid lateral preferential flow and slower subsurface flow. Most importantly, discontinuous storagedischarge relationships at the point-scale combined into continuous relationships at the catchment-scale, a result which can be seen as an emergent property of the Hermine catchment. Copyright (c) 2011 John Wiley & Sons, Ltd.