Investigating the Dynamic Hydrology of Garibaldi Lake
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Investigating the Dynamic Hydrology of Garibaldi Lake By: Tenea Dillman Host Faculty Member: Steve Quane Abstract: Garibaldi Lake is located north of Squamish, BC at an elevation of 1470 meters, roughly 1100 meters above the Cheakamus valley and highway 99. This alpine lake is held in by an archetypically unstable ice-contact volcanic deposit, The Barrier. Springing from the base of The Barrier is Rubble Creek, which is assumed to be the primary outflow from the lake (besides a seasonal overflow stream). Very little is known about the dynamics of this hydrological system, hence I designed a monitoring system to quantify its behaviour. The monitoring system comprises: the volumetric discharge of outflows, volumetric discharge of inflows, and the subsequently changing volume of Garibaldi Lake. Questions explored throughout this paper include: How do seasonal glacial and snowpack melt input affect the water level of the lake and the outflow at both Rubble Creek and the overflow creek? Does Rubble Creek respond to changes in lake behaviour (thus acting as a participant in the hydrodynamic system)? And, is there a correlation between lake level and outflow levels? Using this method, I can begin to monitor intermediate (seasonal) to long term (yearly) behavior of the Garibaldi Lake-Barrier- Rubble Creek hydrodynamic system. Preliminary results show correlation between lake water level behaviour and overflow creek discharge. It is probable that the lake water level is directly responding to glacial and snowpack melt. However, it is yet unclear the degree to which the flow in Rubble Creek dependent on the rest of the hydrodynamic system. Introduction: Garibaldi Lake, elevation 1470 m, is located about 25 km north of Squamish, BC (1100 m above highway 99) and is a popular hiking destination, renowned for its beauty and unique geological origin. Yet, many questions remain regarding hydrological processes controlling its behavior. For example, how do seasonal glacial and snowpack melt input affect the water level of the lake and the outflow at both Rubble Creek and the overflow creek? Does Rubble Creek respond to changes in lake behaviour (thus acting as a participant in the hydrodynamic system)? And, is there a correlation between lake level and outflow levels? To investigate this I designed a monitoring program for the Garibaldi Lake/Rubble Creek hydrological system. The objective of this monitoring system is to answer the above questions. This site is both unique and very interesting due to the lake’s formation through volcanic and glacial activity. During the Pleistocene epoch the land around present day Garibaldi Park was covered by the Cordilleran Ice Sheet (Clague, J., Ward, B., 2012). About 11,000 years ago the combination of both valley and mountain glacier retreat resulted in an ice free window between 1000m and 1500m elevation (Mathews, W.H., 1952). An eruption from Clinker Peak extruded a lava flow which, while flowing down gradient towards the Cheakamus valley, collided with the 1 km thick remnant valley glacier. The lava ponded and solidified in a wall (about 300 m tall) against the glacier, forming the geological phenomenon termed The Barrier. The Barrier acts as a dam in the valley, allowing run off water to collect behind it and form Garibaldi Lake (Mathews, W.H., 1956). The waters comprising Garibaldi Lake are a combination of glacial melt water from Sphinx Glacier, Sentinel Glacier, and small mountain streams. These small mountain run offs arise mostly from precipitation and snow melt. Lake inflow and outflow locations are outlined in Figure 1. Rubble Creek, located to the west of Garibaldi Lake is the main outflow of this alpine lake hydrological system, however there is also a seasonal overflow creek on the western bank of Garibaldi Lake that flows into Lesser Garibaldi and Barrier lakes. Rubble Creek springs from the base of The Barrier at an elevation of about 965 m and flows directly into the Cheakamus River (under highway 99). It has an average flow rate between 2 and 4 m3/s (Quane, S.L. and Stockwell, J. 2014). Garibaldi Lake’s overflow creek is referred to as Rubble Creek in both Garibaldi Provincial Park, Natural History Themes (BC ministry of Environment, Lands and Parks, 1992) and Physical Limnology and Sedimentation in a Glacial Lake (Mathews, W.H., 1956), however, for clarity, I will refer to it as “the overflow creek” as it does not appear to connect to the springs at the base of The Barrier except for during major precipitation events. In this project, I designed a monitoring program for the Garibaldi Lake hydrological system. I created a monitoring method for each component of the model, including the discharge of outflows, discharge of inflows, and the volume of Garibaldi Lake. Using the system detailed below, I can now, for the first time, monitor intermediate (seasonal) to long term (yearly) behavior of the Garibaldi Lake-Barrier-Rubble Creek hydrologic system. Methods: The main goal of this study is to quantify and monitor the inflow and the outflow from Garibaldi Lake as well as the resulting change in lake level. Following, I detail the methods by which I have assessed each parameter. Discharge of Inflows: As seen in Figure 1, Garibaldi Lake has sixteen inflow locations. Due to the steep topography surrounding Garibaldi Lake, it is only possible to measure discharge at two of these locations, Sphinx and Sentinel creeks (represented by IN10D and IN7D, respectively, in Figure 1) on the eastern end of the lake. At those locations, I was able to directly measure volumetric flow rate through the method of salt dilution gauging (Moore R.D., 2003) on June 26th, 2015 and July 21st, 2015. In order to best approximate the total inflow into Garibaldi Lake, I had to approximate flow in the remaining inputs. In order to assess the importance of a certain inflow source, I developed a rating system. I numbered and labeled each inflow according to this system: A- No observable flow, but evidence for seasonal flow (evidence defined as a permanent fluvial channel extending past local snow melt). B- Flowing stream. Estimated rate less than 0.5 m3/s. C- Flowing stream. Estimated rate more than 0.5 m3/s, but less than 1 m3/s. D- Flowing stream. Estimated rate more than 1 m3/s. On June 26th, 2015 and July 21st, 2015 using a 14’ aluminum boat with outboard motor (housed at the lake by BC Parks) I circumnavigated the lake. In this way, I identified and located lake inflows. For each inflow found, I took GPS locations as close to shore as possible, assigned a rating, estimated the flow rate, and photographed the locations. I made estimates visually from the boat, at up to 10 m distance from shore. They are accurate up to 1 sigma. Two exceptions to this method are the Sphinx and Sentinel creeks for which the discharge was measured via salt dilution. Figure 1: Aerial view of Garibaldi Lake and surrounding geological features (49°55’N, 123°02’W) showing input and output locations for the Garibaldi Lake system, obtained from Google Earth (2015). Top of image is North. Each inflow is identified by a blue pin, a number and an importance rating according to the rating system defined in the text. Both outflows are identified by a yellow pin, a number and their name. Discharge of Outflows: Despite the large number of inflow locations, Garibaldi Lake has only two discernable outflows, the overflow creek and Rubble Creek (represented by OUT1 Seasonal Overflow and OUT2 Barrier Spring, respectively in Figure 1). Rubble Creek: As mentioned previously, Rubble Creek springs from the base of The Barrier (Figure 2). It does this in several places, before converging at a point approximately one hundred meters down the valley. The creek is fast moving and turbulent and the creek bed is comprised mostly of boulder cascade morphology. Figure 2: Bird’s eye view of Rubble Creek (looking east). In the background The Barrier exists as a rock face with a large amount of scree around the base. At the bottom of this scree, Rubble Creek emerges and makes its way down the valley. Overflow Creek: Garibaldi Lake’s overflow creek exists seasonally, when snow pack melting and glacial melting occurs (normally May through early October). While not as turbulent as Rubble Creek, during high flow periods the current is strong enough to carry large amounts of debris, evidenced by the several log jams that exist between Garibaldi Lake and Lesser Garibaldi Lake. A foot bridge is installed to allow access to the lake campground on the other side (Figure 3). Figure 3: The overflow creek looking out to Garibaldi Lake (facing approximately west). In the foreground a foot bridge crosses the dry creek bed that will eventually carry overflow water into Lesser Garibaldi Lake. Support beams for this bridge are attached to the rock face and cement footing as seen in Figure 5. In the background Garibaldi Lake remains frozen (photo taken in early May). In order to continuously measure the discharge of Rubble Creek and the overflow creek I employed a Solinst Levelogger Junior Edge (a pressure sensor data logger) and a Solinst Levelogger Edge Barologger (an atmospheric pressure sensor data logger) to each area. Data from the Junior Edge logger is compensated with the Barologger in order to obtain water pressure only. Measurements are made once per hour, on the hour. This provided a continuous data set of stream stage (also referred to as water level). The Rubble Creek level logger and barologger were set up as close as possible to the confluence point of its springs in order to measure only the spring water, which is hypothesized to be coming from Garibaldi Lake, and avoid as much precipitation runoff as possible.