Abstract: A new method has been developed to recognize and understand the temporal and spatial evolution of seawater intrusion in a coastal alluvial aquifer. The study takes into account that seawater intrusion is a dynamic process, and that seasonal and inter-annual variations in the balance of the aquifer cause changes in groundwater chemistry. Analysis of the main processes, by means of the Hydrochemical Facies Evolution Diagram (HFE-Diagram), provides essential knowledge about the main hydrochemical processes. Subsequently, analysis of the spatial distribution of hydrochemical facies using heatmaps helps to identify the general state of the aquifer with respect to seawater intrusion during different sampling periods. This methodology has been applied to the pilot area of the Vinaroz Plain, on the Mediterranean coast of Spain. The results appear to be very successful for differentiating variations through time in the salinization processes caused by seawater intrusion into the aquifer, distinguishing the phase of seawater intrusion from the phase of recovery, and their respective evolutions. The method shows that hydrochemical variations can be read in terms of the pattern of seawater intrusion, groundwater quality status, aquifer behaviour and hydrodynamic conditions. This leads to a better general understanding of the aquifers and a potential for improvement in the way they are managed.

Abstract: Degradation of the quality of groundwater due to salinization processes is one of the key issues limiting the global dependence on groundwater in aquifers. As the salinization of shallow aquifers is closely related to root-zone salinization, the two must be considered together. This chapter initially describes the physical and chemical processes causing salinization of the root-zone and shallow aquifers, highlighting the dynamics of these processes and how they can be influenced by irrigation and drainage practices, thus illustrating the connectivity between soil and groundwater salinization. The processes leading to aquifer salinization in both inland and coastal areas are discussed. The roles of extractive resource industries, such as mining and coal bed methane operations, in causing aquifer salinization are also outlined. Hydrogeochemical changes occurring during salinization of aquifers are examined with the aid of Piper and Mixing Diagrams. The chapter then illustrates the extent of the problem of groundwater salinization as influenced by management and policy using two case studies. The first is representative of a developing country and explores management of salt-affected soils in the Indus Valley, Pakistan, while the second looks at a developed country, and illustrates how through monitoring we can deduce causes of shallow aquifer salinity in the Namoi Catchment of NSW, Australia. Finally, there is a section on integration and conclusions where we illustrate how management to mitigate salinization needs to be integrated with policy to diminish the threat to productivity that occurs with groundwater degradation.