Experimental Environmental Hydraulics: Turbulent Entrainment and Mixing

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Water is not only essential for life and the environment, but also for a functioning infrastructure for society's use. Solutions for the anthropogenic use of water and its impact on surface water resources (lakes, rivers, oceans) are investigated and developed in environmental hydraulics and in water resources engineering. Three problems are addressed in this proposal i) improving pollutant dispersion modelling in surface water, ii) prediction of fluvial erosion of cohesive sediments and iii) assessing and treating metal contamination of drinking water. For applied problems of pollutant dispersion in the hydrosphere, an understanding of the fundamental fluid dynamics of turbulent mixing is required. Two cases in which current dispersion models overestimate dilution are considered. Firstly, momentum jets carrying pollutants are released into turbulent flows in lakes, rivers and oceans, yet the dispersion is currently modelled based on the expedient assumption that the dilution due to turbulent diffusion can be added to the jet driven dilution. Recently it has been shown that, in fact, dilution is reduced in this case, motivating a fundamental study of the change in entrainment for a jet in a turbulent ambient. Second, the mixing downstream of river confluences can result in two streams flowing side by side for up to a hundred kilometers. The fluid mechanics of the mixing layer between the coflowing streams will be studied to understand, and then predict, the reduced transverse mixing occurring in these shallow flows. In water resources engineering, river engineers are finding unexpected river bank erosion in cohesive sediments (clays and tills) caused by higher and more variable river flows occurring due to urbanisation and higher intensity precipitation events due to climate change. As the fluvial erosion mechanisms and thresholds vary as a function of the character and depositional history of the sediment, a field survey will be undertaken to sample a representative number of cohesive sediment samples in the Great Lakes and St. Lawrence Lowlands. The samples will be subject to fluvial erosion tests and geotechnical tests will characterize the sediments allowing the range of behaviours to be classified in order to better predict erosion risk. The provision of an adequate quantity and an adequate quality of drinking water is required to ensure public health. Metal contamination of drinking water is a concern due to it neurotoxicant effect. While the neuro-toxicity of arsenic is well known, copper, although a micronutrient, has recently been linked to Alzheimer's disease. This motivates the development of a cheap point-of-use treatment for arsenic in water using waste shells as the active ingredient, and an investigation of exposure to copper from drinking water and a detailed review of drinking water guidelines.