Model of the Dispersion of Fresh Water and Other Sewage Materials ...

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36 OsmanA. El-Rayis But if the element is not conservative there would be a loss or gain in the concentration at any location en route. Therefore, the equation becomes, C;=F%.Co/100:tUs (3) where Us is the loss or gain in the concentration en route due to.. e.g. biological uptake or addition from other source(s) in the region, respectively. The January 1982 cruise was chosen for investigating the dispersion of phosphate in the surface water of Jeddah coast. It was assumed that vertical mixing in the Jeddah coastal area during this cruise was unimportant in deciding the concentrations of pollutants in the surface water. The percentage of fresh water throughout the surface water of Jeddah coast has been calculated and is shown in Fig. 8b. The fresh water content ranged between 0.5 and 74.8%. The reference source of fresh water of salinity reach 1.8 and it contained 105.6 ~ mole phosphate-P/I (EI-Rayis, unpublished data). Figure 8c, would describe the distribution of phosphate if it were being diluted with a surface Red Sea source having no phosphate and from which biological effects were absent. . The trend in the phosphate concentration and its dispersion in the surface water of Jeddah coast predicted by the model almost follows the trend in the observed concentration (Fig. 8a). This suggests that the differences between the observed concentrations are largely controlled by the mixing of sewage effluents and the Red Sea coastal water. Figure 8d, shows the difference between the measured values and the calculated values of phosphate. This figure, clearly shows areas of negative and positive values, i.e. areas where phosphate is lost or exhausted en route and areas that are affected by contribution from other sources, respectively. The other sources, shown in Fig. 8d, are Lagoon Arbaeen and AI-Hamra District (Fig. 1). One particular source was significant here, the runoff from the coastal Lagoon Arbaeen, that receives domestic sewage effluents mainly from the Eastern Baghdadiah District north of Jeddah City Center, EI-Rayis et at. 1988. The contribution from the other source, AI-Hamra District, seems to be less pronounced than that from the lagoon. Conclusion The dispersion of the pollutants discharged in leddah coastal area is generally controlled by the surface water movement in the down wind; mainly northern to northwesterly winds.. Therefore, the dispersion of the wastes discharged from the present two sources in Bankalah semi-enclosed embayment, its entrance is directed towards northwest, will be hindered during the periods of the prevailing N-NW winds. During the frequent periods of calm or light breeze, or during southern to southeastern winds, the chance then will be greater for the spread of the surplus water from Bankalah zone to the sea as a surface low salinity layer loaded with the sewage materials. The fate and the accumulation site( s) of these wastes in the coastal area need further investigation.
Model oflhe Dispersion of Fresh Waler. 37 Acknowledgement The author wishes to thank Prof. Dr. J.P. Riley, Head of the Oceanography Department, Liverpool University, for critical reading of the manuscript. References Behairy, K.A.A. and Saad, M.A.H. (1984a) Effect of pollution on the coastal waters of the Red Sea in front of Jeddah, Saudi Arabia. 1- Environmental conditions, Tethys, 11: 111-117. Behairy, K.A.A. and Saad, M.A.H. (1984b) Effect of pollution on the coastal waters of Jeddah, Saudi Arabia. 2- Nutrient salts, Tethys, 11: 119-125. EI-Rayis, O.A., Abbas, M.M. and Qurashi, A.A. (1982) Distribution of chemical pollutants in Jeddah coastal waters, Red Sea. 1- Phosphate and silicate, J. Fac. Mar. Sci., Jeddah 2: 73-81. EI-Rayis, O.A., EI-Nakkadi, A.M.N. and Moammar, M.O. (1988) Monitoring and assessment of the water quality of the coastal lagoon "Arabaeen", Jeddah. A report submitted to the Resea1'ch Council of King Abdulaziz University, 40 p. EI-Rayis, O.A., EI-Sayed, M.M. and Turki, A.J. (1985) A preliminary investigation for level and distribution of some heavy metals in coastal water in Jeddah, Red Sea, during 1981-1982, Proc. Symp. Coral Reef Environ. Red Sea, Jeddah, Jan. 1984, pp. 147-169. Ketchum, B.H. and Keen, D. T. (1955) The accumulation of river water over the continental shelf between Cap Coda and Chesapeak Bay. Map. Mar. Bioi. and Oceanogr. Suppl. to V()l. 3, Deep-Sea Res.: 346-357. Morcos, S.A. (1970) Physical and chemical oceanography of the Red Sea, Oceanogr. Mar. Bioi. Ann. Rev., 8: 73-202.
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