Tham khảo tài liệu 'hydrodynamics natural water bodies part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 12 Hydrodynamics - Natural Water Bodies data and the other is the calculation based on estimation of transport parameters such as travel time and dispersion coefficients. Since exact morphological data are often unavailable the parameter estimation technique is more promising. In both approaches tracer experiments are needed to provide field data for water quality models calibration and validation procedures. Indeed model calibration is often a weak step in its development and using experimental tracer techniques the calibration and validation problems can be solved satisfactorily improving the needed feasibility of the early warning systems used by many water supply utilities. Tracer experiments are typically conducted with artificial fluorescent dyes like rhodamine WT Fig. 11 whose concentrations are easily measured with a fluorometre. These tracers should be easily detected non toxic and non-reactive as well as have high diffusivity low acidity and sorption for a quasi-conservative behaviour. Fig. 11. Rhodamine spreading after their injection in a river Mondego reach Based on field experiments data many investigators have derived semi-empirical equations Hubbard et al. 1982 Chapra 1997 Addler et al. 1999 or applied one-dimensional models Duarte Boaventura 2008 to calculate experimental longitudinal dispersion coefficients from concentration time curves at consecutive sampling sites using the analytical solution of first order decay kinetics Table 1 . The injected tracer dye mass must be calculated considering the water volume estimated in the river reach or reservoir system and the fluorometre detection limit. Specific problems of the application of tracers to surface water researches include the photosensitivity of dyes such as fluorescence tracers and recovery efficiency which may imply the use of correction techniques for tracer losses. The tracer mass recovered at each site allowed the assessment of the importance of physical and biochemical river processes
