Modelacao matematica de processos hidrodinamicos e de qualidade da agua no estuario do tejo

STERNA is a modelling system for hydrodynamic and water quality simulations in estuaries where stratification can be neglected. This system consists of an hydrodynamic model, MOHID, previously available, and a transport model and a set of modules for water quality, developed as part of this study. The system is two-dimensional (2 D), depth averaged. The shallow water equations for mass and momentum conservation (hydrodynamic model) and the advection-diffusion equation (transport model) are solved by finite differences. Application of Sterna to the Tagus estuary (Portugal) is described. Results are compared with observations from the campaigns of the "Environmental Study of the Tagus Estuary". These observations comprise: a) time series of currents, salinity, temperature and suspended sediment with a duration of 24 hours; b) series of monthly values of salinity, temperature, chlorophyll-a, phosphate, ammonia, nitrate, BOD and dissolved oxygen with a duration of 4 years. In general, a satisfactory agreement between observations and model results is achieved. Field data and model results are used in a comprehensive analysis of the estuarine environment. The following issues are discussed: tidal exchange between the Tagus estuary and nearby coastal waters; significance of density stratification; heat fluxes across the surface; formation of the turbidity maximum; limiting factors for planktonic primary production; relevant processes in the cycle of phosphorus and nitrogen; origin and significance of oxygen deficits. It is concluded that an integrated approach is important in the study of estuarine processesAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga