2. Study Site
The study is conducted at an unnamed headwater stream in a valley called
Hathataga (meaning huckleberry) by the local Stoney people (Crawler,
Labelle, Mark, & Willie, 1987). Therefore, in this study the stream is
called Hathataga Creek. It is located in the Fortress Ski Area
(50°49’14” N, 115°12’50” W) in Alberta, on the eastern slopes of the
Canadian Rocky Mountains. The stream starts at a set of perennial outlet
springs (Gauging Station 1 (GS1); Figure 1B) and flows north until it
merges with Galatea Creek. The focus of this study is on an 850 m long
reach extending from the outlet springs to a previously installed stream
gauging station (GS4; Figure 1B).
A tarn, with no surface water outflows, is located at a higher elevation
to the south of the springs, separated by a moraine. The tarn, referred
to in this study as Hathataga Lake, forms following snowmelt and dries
up by late summer (Christensen, Hayashi, & Bentley, 2020). As a result
of the hydraulic gradient, the springs drain the sub-catchment that
includes the tarn. This means that in summer months water flows from
Hathataga Lake to the springs.
The spring system consists of numerous discrete discharge points that
combine to form three spring branches (S1, S2 and S3) that merge just
above GS1. The location and presence of these transient discharge points
is dependent on the elevation of the water table. It is important to
distinguish between lake-headed streams and headwater streams as
downstream temperature gradients reflect source water temperature
(Mellina, Moore, Hinch, Macdonald, & Pearson, 2002). Hathataga Creek is
indirectly lake-headed because there is no surface water connection to
Hathataga Lake. Another study at the site determined a travel time from
the lake to the spring system of approximately 4 hours, using a tracer
test (He, J., 2021). Given the horizontal distance of approximately 100
m the hydraulic conductivity of the moraine is on the order of 1 ×
10-2 m s-1.
Elevations in the catchment range from 2034 m.a.s.l at the lower gauging
station (GS4) to 2900 m.a.s.l at the southern headwall. The catchment
has been divided into four sub-catchments (W1 to W4) (Figure 1A).
The bedrock underlying Hathataga Lake and the study reach consists of
recessive shales of the Jurassic Fernie Formation (McMechan, 2012). The
ridges between these valleys are made up of Paleozoic carbonates. The
Sulphur Mountain Thrust separates the Fernie Formation from the older,
more resistant carbonates that make up the headwall in the southern and
western part of the study catchment (Figure 1A).
Surficial sediments and the geomorphology of the area can be attributed
to the late Pleistocene and Holocene glaciations (Beierle, Smith, &
Hills, 2003), which have resulted in the north facing cirque that can be
seen today, along with extensive moraine deposits surrounding Hathataga
Lake. Freeze-thaw weathering of the carbonate headwall has and continues
to contribute to steep talus cones. The coniferous tree line extends to
the base of these talus cones.
The outlet springs discharge at the base of the moraine north of the
lake. Stream geomorphology changes considerably downstream (Figure 2)
(Roesky, 2020). Flow is often turbulent passing through countless pools
and riffles. Between the outlet springs and GS2, the western stream
banks are shallow with numerous visible bank seeps. The eastern stream
banks are typically steeper, incised by 1 to 2 m, with bedrock only
occasionally outcropping. The hillslopes are mostly tree covered but
some segments are covered in alpine meadow on the western side.
Downstream of GS2 the stream gets progressively more incised, by up to
10 m, with increasing bedrock exposure on both sides (Figure 2). Stream
meanders also become more frequent.