Author(s): Ekkehard Holzbecher

Linked Author(s): Ekkehard Holzbecher

Keywords: Density driven flow; Groundwater rise; Land use change; Saltwater intrusion

Abstract: Saltwater intrusion into coastal aquifers is a well-known phenomenon that is aggravated by groundwater pumping, which lowers the groundwater table. Saltwater intrusion has been observed, scrutinized, modelled and methods of combating the further advance of the saltwater front have been proposed and put into action. Natural and anthropogenically increased intrusion can be conceived as two phases of the phenomenon. A third phase can be observed nowadays that is characterized by the rise of the groundwater table. The rise can be attributed to decreased pumping, reduced evapotranspiration, land subsidence (all often accompanying urbanisation of the coastal plain) as well as sea-level rise. The rise of the groundwater table causes several new problems in the affected regions, which are exacerbated by the fact that the rising water is saline. It endangers the foundations of buildings erected in the early phase of low water tables. Saline shallow groundwater seeps into coastal lagoons and depressions affecting eco-systems. In this contribution a numerical model is utilized to demonstrate the three phases of the development of saltwater intrusion and the groundwater table. The model is a modification of the classical Henry model for unconfined aquifers, extended to include temporary groundwater abstraction. The results clearly indicate the different developments of salinity and head in the mentioned phases. Moreover they demonstrate the crucial different behaviours in reaction of a changed pumping regime: the rapid response of the water table on one side and the slow reaction of salinity with a long tailing on the other side.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0230-cd

Year: 2023