The Role of Snow in a Pilot Scale Pit‐Lake Constructed Upland Catchment Within the Athabasca Oilsands Region

ABSTRACT The Athabasca Oil Sands Region (AOSR) is one of the largest unconventional oil reserves in the world. Oil extraction activities have created extensive landscape disturbance, generating ~45 M m 3 of tailings annually. Pit‐lakes offer a reclamation and closure technology solution to meet regulatory requirements, but continued research is required to ensure the design criteria of an upland system can produce sufficient water for maintaining a sustainable and functioning lake. Due to the regional climate within the AOSR, snowmelt often represents the largest single precipitation event across a hydrological year. In this study, the pilot scale constructed system named ‘Lake Miwasin’ was observed across two spring melt periods in 2021 and 2022. The objectives were to: (1) identify the key controls on snow accumulation and (re)distribution; (2) determine the role of antecedent moisture conditions in snowmelt partitioning (storage vs. runoff); (3) assess the ability of the upland catchment to transmit snowmelt to the lake. Field methods included repeated snow surveys, ablation line measurements, snowmelt runoff collection and soil moisture/ice profiling. Results indicate that peak upland accumulated snow water equivalent (SWE) was greater in 2022 (100 mm) than in 2021 (61 mm) with greater accumulation in the low‐lying opportunistic wetlands and swales. Despite the deeper snowpack in 2022, there was proportionally less runoff relative to SWE (0.73) than in 2021 (0.99). This was generally a result of higher rates of infiltration at the hillslope level driven by fall antecedent moisture conditions. Under wetter conditions, there was lower available storage and/or increased ice content restricting infiltration and increasing surface runoff ratios (e.g., North Hummock South Slope: 2021—0.22, 2022—0.17). Despite this, the lake still received sufficient water to restore lake levels to capacity in both years. This study demonstrates that annual snowmelt is a critical component to sustaining the Lake Miwasin water cap, particularly following dry climatic years. Future design considerations should consider incorporating greater features to ensure the maximum accumulation of snow and the highest potential water inflow to the Lake.