Estudo da sustentabilidade do rio Cocó através do método espectral em grade não-uniforme para os cálculos da advecção-dispersão de poluentes

Abstract

The present work represents a study of the resistance of the estuarine zone of the Cocó river in Fortaleza, Ceará - Brazil, to the injection of organic pollutant. In order to accomplish this goal a mathematical model was developed and a C++ code was written to solve the model equations. The flow and pollutant dispersion were simulated for a particular section of the Cocó River under tidal influence. The Saint-Vennant equations were solved using boundary conditions appropriated to that situation. The McCormack’s explicit approach was applied to implement a numerical solution of the equations. The mass transport was simulated by an Advection-Dispersion equation using a first order decay. A pseudo-spectral method with explicit time step was applied and the solution of the system of equations was performed by Gauss algorithm without pivot condensation. The results of the McCormack’s approach were reliable to estimate estuary conditions where the flow was influenced by the tidal movement. The results of Advection – Dispersion (A-D) equations have shown that spectral methods were sensible to the boundary conditions of the problem. On the other hands, the results of A-D equations presented a mass retention in the estuarine zone. That fact lets one to believe that the defined boundary conditions to the problem were not appropriated to that situation. Thus, another boundary conditions were defined by using a hypothetical new estuarine zone ten times bigger than the Cocó River estuarine zone. As a result of that change, the mass retention cease to exist, and the problem became physically correct. The Villela’s (1988) hypothesis on nonstationary behavior of the estuarine zone – Cocó River interface was confirmed.