Precipitation‐Runoff and Storage Dynamics in Watersheds Underlain by Till and Permeable Bedrock in Alberta's Rocky Mountains

Silins

et al. 2020

Preprint

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

Section: Temporal and Spatial Variation In Source Water Signaturesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

Spencer

Silins

et al. 2020

Preprint

“…While some studies have shown the importance of groundwater contributions to streamflow in alpine watersheds in the Rocky Mountains (Hood and Hayashi, 2015;McClymont et al, 2010), the additional complexity imposed by highly heterogeneous glacial till and permeable bedrock in sub-alpine and upper montane watersheds has limited more extensive research on runoff dynamics of this region. As a first attempt to conceptualize runoff generation in Alberta's Rocky Mountains, Spencer et al (2019) quantified storage and precipitationrunoff relationships from hydrometric data. Results indicated that runoff generation was strongly governed by the interaction of two zones of storage -soil and till storage and bedrock storage.…”

Section: Introductionmentioning

confidence: 99%

“…The alpine region and sub-alpine/upper montane region were also identified as two separate hydrologic response units that differed in timing and flow pathways for runoff response. While Spencer et al (2019) developed a conceptualization of runoff generation for this region, they concluded that coupled flow and tracer approaches would be needed to reduce uncertainty in estimated flow contributions from each storage zone.…”

Section: Introductionmentioning

confidence: 99%

“…To expand on recent work carried out in the same study area by Spencer et al (2019), this study aims to advance the conceptualization of runoff generation in the Rocky Mountains in Alberta, Canada. The objectives of this study were to (1) characterize how sources of stream water (rain, snowmelt, soil water, hillslope groundwater, till groundwater, and bedrock groundwater) vary spatially, across four subwatersheds of a Rocky Mountain watershed, and temporally, from spring snowmelt to the start of the next year's snow accumulation period, and (2) determine the relative contributions of source water to the stream from spring to fall for each sub-watershed.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Hillslope and groundwater contributions to streamflow in a Rocky Mountain watershed underlain by glacial till and fractured sedimentary bedrock

Spencer

Hydrol. Earth Syst. Sci.

Silins

et al. 2021

Abstract. Permeable sedimentary bedrock overlain by glacial till leads to large storage capacities and complex subsurface flow pathways in the Canadian Rocky Mountain region. While some inferences on the storage and release of water can be drawn from conceptualizations of runoff generation (e.g., runoff thresholds and hydrologic connectivity) in physically similar watersheds, relatively little research has been conducted in snow-dominated watersheds with multilayered permeable substrates that are characteristic of the Canadian Rocky Mountains. Stream water and source water (rain, snowmelt, soil water, hillslope groundwater, till groundwater, and bedrock groundwater) were sampled in four sub-watersheds (Star West Lower, Star West Upper, Star East Lower, and Star East Upper) in Star Creek, SW Alberta, to characterize the spatial and temporal variation in source water contributions to streamflow in upper and lower reaches of this watershed. 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 water stored in the hillslope over winter (reacted water rather than unreacted snowmelt and rainfall) occurred at the onset of snowmelt before stream discharge responded significantly. This was followed by a dilution effect as snowmelt saturated the landscape, recharged groundwater, and connected the hillslopes to the stream. Fall baseflows were dominated by either riparian water or hillslope groundwater in Star West. Conversely, in Star East, the composition of stream water was similar to hillslope water in August but plotted outside the boundary of the measured sources in September and October. The chemical composition of groundwater seeps followed the same temporal trend as stream water, but the consistently cold temperatures of the seeps suggested deep groundwater was likely the source of this late fall streamflow. Temperature and chemical signatures of groundwater seeps also suggest highly complex subsurface flow pathways. The insights gained from this research help improve our understanding of the processes by which water is stored and released from watersheds with multilayered subsurface structures.

Untangling harvest‐streamflow responses in foothills conifer forests: Nexus of teleconnections, summer‐dominated precipitation, and storage

Goodbrand

Devito

et al. 2022

Hydrological Processes

This study re‐evaluated data from the historical Tri‐Creeks Experimental Watershed (1967–1988) in Alberta, Canada to address the initial question of forest harvest effects on streamflow and investigate the potential influence of teleconnections, summer‐dominated precipitation, and watershed storage on runoff generation. Tri‐Creeks has deep (up to 21 m) glacial deposits underlain by folded and faulted sedimentary bedrock with considerable potential for subsurface water storage. Timing of the conifer forest harvest experiment in two sub‐watersheds (>50% harvested) and one reference occurred near the 1976–77 Pacific Decadal Oscillation (PDO) phase change that led to less snowfall, but little difference in annual precipitation or runoff between phases after harvest. Established statistical and hydrological modelling methods that used regression techniques of observed and simulated streamflow to separately analyse sub‐watersheds did not detect change in average daily or annual runoff due to harvest. The interannual hydroclimatic variability influenced by the climate shift, attenuation of summer precipitation by the drier antecedent conditions in the warm period following harvest, and large potential for subsurface water storage contributed to shifts in runoff and uncertain detection of streamflow response. However, a hydrological modelling approach using calibrated parameters separately in the pre‐ and post‐harvest periods indicate significant change in rainfall‐generated peak runoff events and summer runoff following harvest, which was not detected in the reference watershed. Model calibration required less soil storage capacity in the treated watersheds in the post‐harvest period compared to the reference likely due to reduced transpiration that increased the likelihood of storm runoff during larger summer rainfall events. Within the context of streamflow responses to harvest in conifer dominated forest landscapes with seasonal snow cover, this study illustrates how complexity of climate variability and interaction with watershed storage and continental summer‐dominated precipitation may confound and mask the interpretation of harvest effects in paired‐watershed studies.