The distribution of molybdate-reactive silicate in the receiving waters of an urban sewage outfall on the coast line has been studied. The relationship between silicate and salinity in the mixing zone shows an almost ideal mixing behaviour on the temporal scale (a few hours) of the dispersion area sampled. The profiles along the depth have shown that the greatest amount of molybdate-reactive silicate is transported in the surface waters, and therefore a two-layer model has been chosen to describe this dispersion. The integrated and average depth isoconcentration lines throughout the dispersion layer have been determined under different oceanographic and meteorological conditions. A numerical transport model based on the advection-diffusion process has been applied in order to explain and predict experimental distributions. Wind, boundary conditions and outfall parameters are used as principal variables, providing the isoconcentration lines for an average integrated distribution in the dispersion layer. The agreement between the theoretical and experimental results is better than 75 for the far field and better than 50 for the near field.
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