I'LL BE DAMMED: THE DYNAMIC BEHAVIOUR OF THE GARIBALDI LAKE/RUBBLE CREEK HYDROLOGICAL SYSTEM

Garibaldi Lake is located north of Squamish, BC at an elevation of 1470 meters, roughly 1100 meters above the Cheakamus valley and the Sea to Sky highway (which runs from Vancouver to the resort municipality of Whistler). This alpine lake is dammed by an archetypically unstable ice-contact volcanic deposit, The Barrier. Springing from the base of The Barrier dam is Rubble Creek, which is assumed to be the primary outflow from the lake (besides a seasonal overflow stream). Despite Garibaldi Lake being a very popular tourist destination, little is known about the dynamics of this hydrological system. As a result, we designed a monitoring system to observe its behaviour. The system comprises: volumetric discharge of inflows, volumetric discharge of outflows, and the subsequently changing level and volume of Garibaldi Lake. We document sixteen inflow sources seasonally filling the lake and two outflow sources, one of which drains continuously from beneath the natural lava dam (Rubble Creek) and the other comprising seasonal overflow. We collected continuous stream stage for both the seasonal overflow stream and Rubble Creek over a six month period. During that same interval, we also measured lake level. All water level data is collected once per hour, thus providing a continuous data set. Volumetric discharge in the outflow streams is interpolated using a discharge/stage curve and calibrated using periodic direct discharge measurements using the salt dilution method. Using the data obtained through our monitoring, we created a water balance model describing the transfer of water throughout the hydrologic system. Preliminary results show a predictable correlation between lake water level behaviour and overflow creek discharge, both likely in direct response to melting of seasonal snowpack and glacial ice. In addition, lake water level drops steadily during low inflow periods and continues dropping even after the overflow stream ceases to flow (to levels much lower than the overflow stream threshold); Rubble Creek flow remains relatively constant throughout the data collection period. These observations allow us to extrapolate temporal water flow and gain a more comprehensive understanding of the hydro-dynamics within this system.