TR(BR)-6/98-99 : Salt water intrusion in coastal aquifers

Abstract

Eco-friendly and sustainable management of water resources is indispensable in coastal and deltaic regions due to their unique nature of hydrological processes and economic significance. Since coastal areas are characterised by the interaction of land, sea and atmosphere, management of such zones requires management of all the interactive components in a rational and comprehensive manner. Thus, environmental management of coastal areas presupposes management of coastal waters, coastal lands and coastal ecosystems. Among various hydrological problems needed to be addressed in the coastal regions, salinisation and associated issues draw special attention. Quantitative understanding of the pattern of movement and mixing between fresh and saline water, and of the factors that influence these processes, is required to manage and protect the freshwater resources in the coastal regions. A sustainable groundwater development and management programme in coastal aquifers should therefore aim at maintaining an acceptable spatial and temporal equilibrium of saltwater ingress in the aquifer system at a regional scale while ensuring quality standards in the pumped water. Such objectives necessitate analysis of the saltwater intrusion problem at regional scale as well as at local scale. Remedial measures are devised/ evaluated after performing a prognostic analysis of the problem using field data and hydrogeological information of the aquifer system. Mathematical modelling of flow and solute transport in coastal aquifer systems can assist greatly to achieve this end. In the present study, saltwater intrusion processes in a (hypothetical) homogeneous and multi-layered coastal aquifer system are simulated using the USGS finite element model for "saturated-unsaturated fluid density-dependant groundwater flow with energy transport or chemically reactive single species solute transport" (SUTRA) for different boundary conditions and aquifer parameters. The saltwater intrusion profiles for steady-state/ transient conditions are obtained and analysed. The effects of changes in the permeabilities of aquifers and aquitards, changes in the influx at the boundary, and changes in dispersivities in the medium on the saltwater intrusion process are investigated. The effect of material-independent/ material-dependent dispersivities are also subjected to analysis. It is inferred from analyses that permeability of the medium. dispersivity in the medium and influx at the boundaries affect the extend and intensity of saltwater intrusion in a coastal aquifer system. However, material dependent dispersivity in a multilayered aquifer system did not make discernible changes in the intrusion profile compared to that with material-independent dispersivitiy for the present set-up. Elaborate discussion of results and analyses are presented in the report with the aid of tables/ plots.