ABSTRACT: Spring flood reconstruction from ice scar chronologies: the example of Lake Montausier, northeastern Canada.

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Abstract

Context. Spring ?ood is a dominant component of the hydrological cycle in northern environments. In addition to their well-recognized impacts on riparian environments and communities, spring ?oods are of critical economical importance, especially in northern Québec, where the in?lling of the vast hydroelectric reservoirs strongly depends on the water supplies at snow melt. Objectives. This study aims at reconstructing the spring ?ood variability since AD 1850 for the upstream section of the LaGrande hydroelectric complex in northern Québec. We used discrete dendrogeomorphological indicators such as the proportion (It) and maximal heights (Ht) of ice-scarred trees sampled around Lake Montausier, a small water body whose yearly (spring) hydrological ?uctuations are hypothesized to be of “regional signi?cance”. Methods. We developed a novel reconstruction model to take into account the various sources of uncertainties involved throughout the modeling process. Such uncertainties are: (1) a possible error in the estimation of It and Ht from ?eld data, (2) error of generalizations (e.g. applying a model to an independent dataset). We also introduced a new regression technique, namely Generalized Additive Models (GAMs), that enable the modeling of the non-linear relationships that naturally occur in such environments. All these techniques are implemented in a new algorithm called GLAMODEL (programmed in R). Results. Discharge reconstructions performed from GLAMODEL suggest that, since the 1930s, spring ?oods became more intense and also more variable. Periods of high spring discharge were documented for the 1880s, 1930-1940s and 1960-1970s periods. The 1947, 1960 and 1979 spring ?ood events were unequalled in magnitude over the last 150 years. These results support the past trends documented from other proxys (tree-rings) and in similar studies using ice scars in nearby environments. The novel aspect, however, is that variations in It and Ht are directly translated in terms of past discharges which makes them readily available for water resources managers.

Bibliography of Canadian Geomorphology