Comparative study of fecal bacterial decay models for the simulation of plumes of submarine sewage outfalls.

In the literature, analytical models have been shown to be extremely useful for estimating the decay rates of coliform as fecal indicator microorganisms, providing reliable predictions of bathing conditions in coastal and continental waters. Although a number of different formulations have been developed in the literature, each one may only be suitable for specific environments, and no comparison between these methods has ever been carried out. In the present article, a comparative analysis of bacterial decay models, calculated by eight different formulations, was performed in coastal outfall plumes, considering identical environmental conditions of solar radiation, temperature and salinity. A statistical approach was applied to identify the differences in means and in behaviors of the results obtained in the various simulations. The results indicate good agreement between bacterial decay rates calculated with at least four methods that were considered more reliable, and at least one of the models was shown to be suitable for estimating bacterial decay rates under night-time conditions, considering only the combined influences of temperature and salinity. Moreover, under daytime conditions, it provides consistent decay rates when compared with measurements taken in the field.

A semi-implicit finite element model for natural water bodies.

In this work, a semi-implicit model, applied to the shallow water equations, is developed for natural water bodies. In the proposed model, the shallow water equations are integrated in the vertical direction, finite elements are employed in the spatial discretization, and finite differences in the time discretization. The model is based on the uncoupling of the governing equations, in which the expressions of the velocity components, obtained explicitly from the discretized momentum equations, are substituted in the continuity equation. Therefore, there is an uncoupling of the solution; initially the continuity equation is solved, and, in the sequence, the momentum equations are solved. Yet, this uncoupling produces a significant reduction in the number of equations of the resulting systems, when compared to standard coupled systems. This reduction improves substantially the computer performance.