Permafrost

144
Theme 4. Permafrost hydrology and
cold regions water resources and land use
Impacts of an Arctic Reservoir’s Regulation on Downstream Thermal
Regime in Open-Water Season
Baozhong Liu and Daqing Yang
(Institute of Northern Engineering, University of Alaska Fairbanks, Fairbanks, AK 99775, USA)
Abstract: In this study, based on the long-term (1950-1990/1992) stream temperature and
discharge data, we investigated the impacts of the Vilui reservoir’s regulation on the
downstream thermal regime in the open-water season. Results show that in the early
open-water season (before June 30), the reservoir’s regulation has enhanced the downstream
water temperature in a length through the mid Vilui River (maximum 4.7 o C) and down to the
river mouth (maximum 2.3 o C). The decrease of discharge due to reservoir’s regulation is
mainly responsible for the downstream water temperature increase in June, which was defined
as the “indirect impact” of the reservoir. Analysis shows that the “direct (positive or negative)
impact” of the reservoir, which usually causes continuous temperature increase or decrease
along a distance of the downstream from the dam, could be possible in a distance from the dam,
though much likely shorter than the mid Vilui River in the early open-water season. Results
reveal that part of water temperature increase (around 1 o C) at the Vilui River mouth in June is
caused by natural factors. In the mid open-water season (from July 10 to August 10), the
reservoir’s regulation has reduced the downstream water temperature in a length through the
mid Vilui River (about -2.7 to -0.6 o C), but not down to the river mouth. The “direct (negative)
impact” is primarily responsible for the water temperature decrease in the mid open-water
season in the mid Vilui River as the discharge increase is small compared to the pre-dam period.
It is important to note that the water temperature in July at the Vilui River mouth is significantly
associated with the reservoir’s regulation (discharge variation), although the long-term mean
water temperature doesn’t show big change compared to that in the pre-dam period. In the late
open water season (after August 20), the impact of the reservoir’s regulation cannot be through
the mid Vilui River; thus the water temperature increase at the river mouth shows a local
warming (maximum 1.9 o C), which is probably due to the reduction of influx from the
non-regulated area.
Key words: Vilui River, Reservoir Impacts, Thermal Regime, Long-term Change