Sheena Spencer | ALES Graduate Seminar

A graduate seminar is a presentation of the student’s final research project for their degree.  This is a PhD Final Exam Seminar by Sheena Spencer.  This seminar is open to the general public to attend.

Thesis Topic: Runoff generation in a steep snow-dominated watershed in Alberta’s southern Rocky Mountains

Sheena Spencer – PhD with Dr. Axel Anderson and Dr. Uldis Silins

Abstract:

Runoff generation in a steep snow-dominated watershed in Alberta’s southern
Rocky Mountains

Star Creek is a snowmelt-dominated, steep mountain watershed with shallow soils, deep glacial till, and
fractured sedimentary bedrock in the eastern slopes of Alberta’s Rocky Mountains. Measurements of
streamflow quantity and chemistry at variable scales, water table dynamics, and precipitation were used
to describe the first order controls on runoff generation in Star Creek watershed and its sub-watersheds.
Specifically, 1) precipitation-runoff relationships and watershed storage were quantified; 2) timing and
drivers of hydrologic connectivity were identified; and 3) source water contributions to streamflow were
estimated. Multi-year precipitation patterns changed from dry (2008-2012) to wet (2013-2014)
conditions and caused an increase in unit area discharge for all but one sub-watershed. Despite a
change in annual flow contribution and total discharge, event-scale rainfall-runoff responses did not
change. The annual snowmelt pulse saturated the landscape, created the main period of hydrologic
connectivity in the watershed, and controlled the magnitude of event-scale rainfall-runoff responses.
Streamflow contributions did not correlate with upslope accumulated area. Rather, the overall
watershed structure, groundwater upwelling, and the distribution of snowmelt processes influenced the
quantity of streamflow contributions. Two locations of subsurface storage were identified: shallow
subsurface storage and bedrock storage. Shallow subsurface storage includes the soil and glacial till
layers and influences event runoff, hillslope connectedness, and the carry-over of precipitation effects
from fall to the next water year. Bedrock storage influences annual discharge because of the dominance
of vertical percolation and groundwater recharge and high annual groundwater contribution to
streamflow.

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 the main
snowmelt freshet streamflow pulse was generated by large volumes of snowmelt in the upper
elevations and alpine zone. Late summer streamflow was dominated by either soil drainage or
groundwater that was recharged in the alpine zone. In Star East, fall baseflows were dissimilar from all
measured sources, but groundwater seep temperatures suggest that it was likely from a deeper
groundwater source. While other studies suggest that glacial till groundwater contributes to late season
baseflows, there was no evidence that it meaningfully contributed to stream water at any time of the
year.