Desalination of seawater leaves brine waste containing a high salt concentration to be disposed of into the environment. For coastal desalination plants, the most practical and least expensive brine disposal operation is to discharge it into the sea. Modeling studies on the effect of coastal water depth variations upon mixing and spreading of brine waste continuously being discharged into the sea are presented. Solutions are illustrated graphically, showing that the brine plumes are spreading downstream and heading towards the beach. For Oman in particular, the increase in salinity in coastal water will intensify the critical problems of seawater intrusion into coastal groundwater aquifers. However, this potential impact of brine disposal operations on coastal and marine environment can be alleviated by building longer sea outfalls.