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A B S T R A C TLake eutrophication has proven to be a stubborn environmental problem. Depletion of dissolved oxygen (O 2 ) in the deep layer (hypolimnion) of lakes during stratification and its deleterious effect on fish stocks have been observed and analyzed for more than 100 years. Although it has taken only 60 years for humans to turn many freshwater lakes eutrophic, studies estimate that their recovery may take 1,000 years under the best circumstances. In deeper (thermally stratified) lakes, the stabilization can involve several factors, including biogeochemistry of the deep layer of water (hypolimnion), temperature of the hypolimnion, shape of the lake basin, abundance of rooted plants, and food web structure. The main purpose of this study was to show the efficiency of hypolimnetic aeration process on the preservation of the thermal stratification, the increasing the amount of oxygen dissolved, and the reduction in phosphorus in the depths of the lake. The 10.3 km 2 of the water of Hallwil Lake is an important tourist center for the Canton Aargau (Switzerland). In fact, fishing and water sports are practiced. Before its restoration in the winter of the year 1985/1986, this lake's eutrophication showed significant disruption of aquatic activities, and pollution damage due to its various uses, and thus inhibited the development of tourism in the region. In order to address the eutrophication of Hallwil Lake, the Canton Aargau put into service in the winter of 1985/1986, an installation of a aeration system in two alternate modes of aeration namely by a aeration system in winter destratification and aeration hypolimnetic in summer (air/pure oxygen). As a result, the values of the concentrations of dissolved oxygen during the aeration are as follows: [O 2 ] min ≥ 4.5 g/m 3 in the spatial variation and 5 g/m 3 in the temporal variation. Also, the heating of the hypolimnion has not attained the thermocline, and as a result, the thermal stratification is preserved.

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Thermal stratification of lakes and reservoirs can result in substantial hypolimnetic oxygen depletion, which may have a negative impact on the cold-water fisheries, the drinking water treatment process, and water quality downstream of hydropower reservoirs. Several techniques of aeration are presented in this study, to describe their effectiveness in control of physical and chemical parameters, that compromising the balance ecological and the thermal stratification in water supplies. As a result, we demonstrate that the most efficient hypolimnetic aeration system is the bubble plume diffuser; although an accidental destratification may occur. In hypolimnetic aeration systems, the aeration system by bubble plume appears to be the most economic and perhaps the simplest among the systems used in Stanley lake (Colorado, U.S.A), even as other researches select Speece Cone aeration system, or the full airlift systems, or the TVA line diffuser. The purpose of this study is to show the oxygen transfer efficiencies in the different methods used in the technique of hypolimnetic aeration, and their effect on the preservation of the thermal stratification. As well, this study concentrate on the economic and technical sides associated to these aeration systems.

Notre travail présente une étude expérimentale du dépôt de particules colloïdales dans un milieu poreux consolidé, homogène et initialement saturé en eau. La phase fluide injectée dans le milieu poreux est une suspension de particules de latex dont la dimension est connue. L'influence de la force ionique de la suspension colloïdale et du débit d'injection sur le dépôt de particules est étudiée. On observe que le recouvrement de surface (θ) croît avec la force ionique alors que le recouvrement de surface (θ) décroît quand le nombre de Péclet augmente. Des mesures locales, par atténuation d'un rayonnement γ, mettent en évidence la réduction de porosité due au dépôt de particules. La réduction de la perméabilité, mesurée en fin d'expérience.