Tidal Flushing Characteristics of Municipal and Industrial Waste in the Karachi Coastal Waters and Simulation of Waste Field Dilution at Sewage Outfall

The deterioration of Karachi coast and the marine environment near to it cannot be ignored. Effluents from industries and untreated sewage discharge into the coastal waters through Malir and Lyari Rivers and this ultimately have a negative impact on marine life and also to human health. The toxicants present in the industrial wastewater play a vital role in declining the marine population and also cause contamination. The knowledge of flushing and residence times of estuaries and creeks is very important. However, the estimated flushing time by using the freshwater fraction method ranges 15-20 days at both sites. The freshwater fraction method is considered to be a reasonable estimation method as in this method salinity variation in the estuary and open sea are also incorporated in the calculation. Discharging the effluents in the estuary results the destruction of the ecosystem of the area. Thus the discharge of polluted water directly in the deep offshore water certainly improves the quality of life in the coastal areas. Therefore, submarine outfall construction is an effective way to discharge the sewage far away from the coast where diffusion, dispersion and dilution are enhanced. This paper deals with the estimation of flushing time scales and marine environmental parameters in the offshore waters of HawkesBay and Gizri creek/DHA coastlines. The outfall model, DESCAR, is used to determine the spreading and dilution of pollutants under different oceanographic and meteorological forcing. The other outfall parameters such as Initial dilution and Froude numbers and return back travel time are also estimated by using USEPA spread sheet and the ocean-atmosphere archived data. (author)