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Auflistung nach Autor:in "Hejzlar, Josef"

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  • Konferenzbeitrag
    Modelling the Hydrodynamics and Water Quality of the Vltava River Reservoir Cascade
    (Informatics for Environmental Protection - Networking Environmental Information, 2005) Růžička, Martin; Hejzlar, Josef; Jarošík, Jiří
    Mathematical modelling is an efficient tool for evaluation of impacts of human activities and environmental changes on water quality in rivers and reservoirs. This contribution describes simulations of water quality in the Vltava River reservoir system, namely cascade of reservoirs Hněvkovice, Orlík, Kamýk, Slapy, Štěchovice, and Vrané. The twodimensional water quality model CE-QUAL-W2 was used for this task over years 2000 to 2003. Sensitivity analysis, calibration, and evaluation of the model were done. The model gave good results in particular for hydrodynamics, water temperature, and conservative constituents because of good quality of available hydrological and meteorological input data. The accuracy of results was strongly depended on the quality of input data and sampling frequency. Minor problems occurred in water quality simulations based on monthly input data in periods with fluctuating discharges.
  • Konferenzbeitrag
    Nutrient Retention – A Key Element in Evaluating Reference Conditions of Lakes and Reservoirs for the EU Water Framework Directive
    (The Information Society and Enlargement of the European Union, 2003) Hejzlar, Josef; Boers, Paul; Kronvang, Brian; Karaer, Feza
    A set of P and N retention data from 178 lakes and reservoirs was analysed using a simple mass balance model requiring knowledge only of water residence time, mean depth, and average mass transfer coefficients for P and N loss (vP and vN, respectively). The model for P retention was refined by categorisation of water bodies according to their input P concentration into three classes, i.e. <10, 10-35, and >35 μg l -1, with corresponding vP values of 7, 15, and 40 m yr -1, respectively. The model for N retention used only one vN value (8 m yr -1) for all water bodies. The absolute mean error of the models was within the range between 9 and 19% of the calculated retention values. The models are suggested for use in determining reference conditions of natural and artificial water bodies within the application of the EU Water Framework Directive in the Czech Republic legislation.