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| activités | bourse | liens | membres | contact | ||
date |
Mardi, 18 mars 2008 |
lieu |
INRS-ETE
(salle 2417) |
| heure
|
12h15 |
| Daniel
L. Peters Aquatic
Ecosystem Impacts Research Division of Environment
Canada
|
|
Hydrological
Role of Obstructed Drainage and Reverse Flow Contribution in
a
Northern River-Lake-Delta Complex
|
A
distinctive hydrological feature of the Lake Athabasca - Peace-Athabasca
Delta (LA-PAD) complex is that flow in the channels that drain the system
reverses direction when stage on the Peace River is higher than for the
central lakes. The hydrology of this river has experienced natural and
human induced changes since 1968 that have led to decreased peak flows.
Outflow control structures were installed in the mid-1970s to counter
enhanced drainage of the LA-PAD associated with hydroelectric operations
in
the headwaters of the Peace River. This study investigates the importance
of spring break-up and open-water induced outflow obstruction and reverse
flow contributions to the generation of annual lake level maxima under
natural (1960-67), regulated (1976-04) and naturalized (1976-96) flow regimes. Obstructed and reverse flow events during the spring break-up period were common prior to and following flow regulation, suggesting that the hydroclimatology in the areas below the W.A.C. Bennett Dam exerted a strong influence on their occurrence. Correlation analysis revealed that antecedent hydrological conditions, such as fall freeze-up lake level, river-ice break-up magnitude, and initial open-water lake level, were significantly associated with annual lake level maxima. During the summer period, sustained high flows on the Peace River were important to the magnitude of lake level generated. The river obstructed outflow and contributed reverse flow to the LA-PAD in each year prior to 1968. Following regulation, however, more than half the years did not experience any obstruction and/or reversal, and those that did were characterized by smaller events. The average estimated duration of obstruction was more than two weeks shorter and the volume of reverse flow was reduced by ~90% under a regulated regime as compared to a simulated naturalized flow regime. A consequent implication was a lowered potential for lateral lake expansion into the delta floodplain in most years. The regulated hydrology was capable of producing large stormflow and high lake levels, but only under atypical hydroclimatic events in the areas below the dam and/or human-induced circumstances that altered normal reservoir operation. During drought periods, the LA-PAD levels were influenced by outflow control structures to help store direct inflows and reduce outflow from the system. |
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