Theoretical Distribution Of Silicate In An Urban Sewage Outfall, Correlation With Experimental Data

Abstract

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 proflles 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 !ayer have been determined under different oceanographic and meteorological conditions. A numerical transport model based on the advection-diITusion process has been applied in arder 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 !ayer. Thc agreement between the theoretical and experimental results is better than 75 􀉩·􀉪 for the far fíele! and better than 50 °0 for the near field. Finally, given these conditions, a conservalive behaviour of the silicatc can cxplain lhe experimental distributions in thc mixing zone uf an urban sewage outfall within a reasonable margin of error.