Partitioning impacts of climate and regulation on water level variability in Great Slave Lake

Water level observations and a daily water balance model are used to build a naturalized water level history for Great Slave Lake dating back to the 1967 completion of the W.A.C. Bennett Dam in the Peace River basin headwaters. Comparison of water level observations dating back to 1938 and water balance scenarios for 1964–1998 assist in constraining the probable magnitude and likely direction of climate and regulation impacts on the water level history of the lake. Overall, the first-order analysis suggests that the effect of flow regulation has been to dampen annual water level variability by about 20 ± 2 cm, to reduce annual maximum water levels by about 14 ± 3 cm and to shift peak water levels earlier in the season by about 30 ± 8 days. Meanwhile, climate forcing has tended to enhance water level variability by 8 ± 2 cm, to enhance maximum water levels by 10 ± 3 cm and to advance the timing of maximum water levels slightly (11 ± 8 days). Climatic and regulation impacts appear to have generally counter-balanced changes in amplitude of water level changes and magnitude of peak levels but have cumulatively contributed to a seasonal shift toward earlier peak water levels in the lake.