Techniques de marquage pour l'etude des circulations des masses d'eau dans les lacs. Application a la retenue de Pareloup

Abstract

Companies like EDF, managing water resources from lakes or reservoirs, are concerned to maintain the balance of lake ecosystems. The protection of environment requires a good knowledge of ecosystems, associating several scientific fields in experimentation and mathematical modeling. Tracing technics with dyes have been applied for studying water circulations in lakes in order to understand better the physical processes simulated by the thermal and hydrodynamical models. The first part of the paper presents tracing methodology using dyes, their choice and implementation, the technics for locating and following up the plume, sampling, measuring and interpreting. The second part presents the results of experiments. In the case of water injection by a pumping station at the bottom of the dam, the plume created is guided by water density and geometry of the bottom of the lake; it remains below the thermocline, because of the strong density gradient, and moves horizontally at the same elevation. In the case of a narrowing of the lake geometry, the wind induces horizontal and vertical loops, into epilimnion and hypolimnion without any water exchange across the thermocline. These particular circulations occur when the water body is well stratified and under strong winds. They are widely responsible for horizontal homogeneity and autumn destratification by shear. This study contributes to improve scientific knowledge and to test application of tracing technics with dyes to natural ecosystems.