Seasonally varied hillslope and groundwater contributions to streamflow in a glacial till and fractured sedimentary bedrock dominated Rocky Mountain watershed

Abstract

Whereas a lack of streamflow response to significant forest disturbance (e.g., forestry, wildfire, and insect infestation) has been observed at multiple locations in the Canadian Rocky Mountains, a region with sedimentary bedrock 10 overlain by glacial till, mechanisms governing this lack of change remain unclear. Some inferences can be drawn from conceptualizations of runoff generation (e.g., runoff thresholds and hydrologic connectivity) in physically similar watersheds, although much of the focus has been on rainfall-runoff dynamics. Thus, there is a need to describe runoff generation in this snow-dominated area to interpret how forest disturbance may impact streamflow quantity for downstream users. Stream water and source water (snow, rain, hillslope groundwater, till groundwater, bedrock groundwater and seeps) were sampled in four 15 sub-watersheds (Star West Lower, Star West Upper, Star East Lower and Star East Upper) in Star Creek, SW Alberta. Principal component analysis was used to determine the relative dominance and timing of source water contributions to streamflow over the 2014 and 2015 hydrologic seasons. An initial displacement of old water stored in the hillslope over winter occurred at the onset of snowmelt, before the stream responded significantly. This was followed by a dilution effect as snowmelt saturated the landscape, recharged groundwater, and connected the hillslope to the stream. Fall baseflows were dominated by either hillslope 20 groundwater or bedrock groundwater in Star West. Conversely, in Star East, stream water was similar to hillslope water in August but was unlike the measured sources in September and October. Temperature and chemical signatures of groundwater seeps suggest highly complex subsurface flow pathways. Hydrologic resilience in the Rocky Mountain eastern slopes may be, in part, due to these complex subsurface pathways in combination with the slow release of groundwater from glacial till. 25

Streamflow response to native forest restoration in former Eucalyptus plantations in south central Chile

“…Streamflow percent increases in response to native forest restoration were highest at two catchments (RC5 and RC10) which had the least base flow, as indicated by low runoff ratios and high summer base flow sensitivity to variation in precipitation, whereas streamflow responses were lower at the restored catchment (RC11) which had the greatest base flow, as indicated by high runoff ratio and low summer base flow sensitivity to variation in precipitation (Figure 4, Table 3, Figure S6 in Data S1). These findings are consistent with other studies showing that catchment hydrology can moderate streamflow response to change in vegetation and climate (Spencer et al, 2020; Tague et al, 2008; Vose et al, 2016).…”