Salinity dynamics as a tool for water resources management in coastal zones: An application in the Tramandaí River basin, southern Brazil

Coastal zones are transition environments, forming the interface between continent and ocean. The effects of human activity on coastal water resources usually reduce the flows of freshwater to estuaries, modifying estuarine mixing processes and extending marine influences further inland. This dynamic can adversely affect water availability in the coastal zone. To manage coastal water resources, a mass-balance model has been used to describe the dynamics of salinity in the estuarine system of the Tramandaí River, southern Brazil. The output from the model is used to assist the integrated water resources management within the Brazilian context. From the salinity model it was possible to define the estuarine area and its relation to the critical water body for management purposes, the Passo Lagoon. Modelling the salinity dynamics was shown to be useful for identifying procedures needed for managing water resources in coastal basins. Permits to abstract water can be used to limit withdrawals, so as maintain the flows needed to limit saline intrusion. With the classification of water bodies, the maximum saline load that each water-body can bear without changing the environmental can also be identified. Monitoring can be used to maintain saline levels in water that are adequate for the purposes intended. The methodology has been shown to be useful for integrated water resources management, providing a link between existing procedures and the particular characteristics of coastal basins.

► Salinity dynamics was proposed for water resources management in the coastal zone.
► Salinity was shown to be a good environmental indicator.
► The salinity dynamics determines the water-bodies whose management is critical.
► The permits to use of water resources should consider the salinity dynamics.
► The salinity dynamics can be much useful for the basin committee.