Naidu, V.S., 2013. Estimation of near-field and far-field dilutions for site selection of effluent outfall in a coastal region—a case study.

Site selection for release of industrial effluents is of prime concern for maintaining the quality of the marine environment. In this study, an attempt has been made to establish the prevailing ecological conditions and to suggest the suitable location for discharge of the effluents into the sea by using near-field and far-field models. Near-field dilutions were calculated using a buoyant jet model, whereas far-field dilutions were estimated using a two-dimensional numerical model. As a case study, the location of outfall is to be suggested to Vapi Waste and Effluent Management Company Ltd. (VWEMCL) for the release of treated effluents. At present, VWEMCL is discharging effluents upstream of the Damanganga estuary. As a result, the entire Damanganga estuary has poor water quality. Field studies conducted in 2009 suggested that the Damanganga estuarine segment is more polluted than coastal waters. Near-field model studies show that the effluent would attain 35–70 times dilution depending on the height of the water column if the release is made at the offshore location. A far-field model study revealed that the effluent would be diluted effectively with ambient currents, and the near ambient conditions would prevail at around 100 m distance. The effluent would move along the coast, and chances of reaching to the estuary are remote. Rise of the biological oxygen demand concentration to 2.9 mg/L above ambient is predicted at the release site. The water quality of Damanganga estuary would be restored to the preindustrial period once the outfall is commissioned.