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TitreReconstruction of past hydrology in the James Bay Hydroelectric complex over the past 200 years
AuteurBégin, Y; Arseneault, D; Bégin, C; Boreux, J -J; Boucher, E; Cournoyer, L; Dy, B; Gingras, M; Guiot, J; Lemay, M; Marion, J; Nicault, A; Perreault, L; Roy, R; Savard, M
SourceArcticNet 2006 Annual Scientific Meeting: programme /ArcticNet Réunion scientifique annuelle 2006 : programme; 2006 p. 14-15
LiensOnline - En ligne (pages 14-15)
Séries alt.Secteur des sciences de la Terre, Contribution externe 20080150
RéunionArcticNet Third Annual Scientific Meeting; Victoria; CA; décembre 12-15, 2006
Documentpublication en série
Mediapapier; en ligne; numérique
Sujetspropriétés hydrologiques; milieu hydrologique; potentiel hydroélectrique; énergie hydroélectrique; bassins versants; niveaux d'eau; précipitation; profondeurs des eaux lacustres; climat; hydrogéologie
Résumé(disponible en anglais seulement)
In the last two centuries, we have witnessed change in the water supply in the watersheds of northern Quebec. This change is recorded in the natural archives such as dendrochronological indicators derived from lake shore trees. In order to retrace the evolution of the hydrological regime parameters with time, we have reconstructed the main hydroclimatological variables used in forecast models. The study was conducted in the region of the James Bay hydroelectric complex of La Grande. Three types of proxies were used. The first one was the position of the tree line on the lakes shores. This position indicates that lake levels have been rising due to higher precipitation. The episodes of colonization and retreat indicate that prolonged episode of low water levels have occurred seven times in summer in the last two centuries. However, these summer low levels are only a negative incursion in the positive trend towards higher lake levels mainly related to higher snow precipitation. This last information is inferred from ice-scarred trees, the second type of proxy studied. Ice scars allow the dating and evaluation of the amplitude of high snow levels in the last centuries. River floods are explained by different hydrological processes but can be dated with the same method demonstrating the same rising trend for the last two centuries. In the absence of instrumental data, the use of discrete events give the possibility of dating hydroclimatological extremes, detecting changes in the precipitation regime and evaluating the range of variability in time and space. The third type of proxy comes from dendroclimatology. Trees occupying sites sensitive to water availability variations (xeric, mesic and hygric sites) and those sensitive to thermal conditions (depending on exposition) give the opportunity to reconstruct climate variability between years. A calibration period with instrumental data is essential and it is also important to verify the models relating rings to climate with independent data. A widespread network of measuring sites allows the evaluation of the spatio-temporal variability of these indirect climate markers. More than one hundred tree-ring series covering more than 180 years, tens series of more than 250 years and two series covering almost one thousand years have been reconstructed. These tree-ring series cover an area of 320 000 km2 (800 km in longitude x 400 km in latitude). Our aim was to reconstruct quantitatively the main variables used in hydrologic forecast models as identified by a research team from Ouranos and Hydro-Quebec. The main variables are summer temperatures, snow precipitation and seasonal water supply. The tree-ring proxies used were ring width, density (9 derived variables) and the ratios of the stable isotopes of oxygen and carbon. The first step of the study consisted in finding and analyzing all instrumental data available for the area. This first step had double results. It permitted to obtain all validated data used in the calibration of tree-ring series and in the construction of the models relating tree-rings, hydrological conditions and climate. It also allowed establish the scientific basis of a northern network of hydroclimatological data taking into account the spatio-temporal representativeness of the available data. The second step of the study was to unravel the meaning of each proxy and model the relationship between tree-rings, hydrological conditions and climate. Finally, the third step consisted in using all proxies to reconstruct past conditions for the period before the availability of instrumental data. We could in this way determine the evolution of hydrological and climatological conditions for the last two centuries.