Salt-wedge dynamics in microtidal Neretva River estuary

Abstract The Neretva River estuary, located in Croatia, on the eastern coast of the Adriatic Sea, is a typical example of a micro-tidal salt-wedge estuary. The analysis of the salt-wedge dynamics in the Neretva River estuary is a crucial element in planning, designing, and managing the irrigation system in this coastal region. This analysis also provides essential information for the sustainable development of agriculture and the protection of water resources. Furthermore, the Neretva River is closely linked to the seawater intrusion through the aquifer and the resulting groundwater and soil salinization during the summer when the salt-wedge intrudes more than 20 kilometers inland through the main channel. Therefore, to better understand the physical processes and establish a reliable framework for future activities and research of the saltwater intrusion, the salt-wedge dynamics in the Neretva River estuary was investigated based on continuous field measurements and numerical modeling for the period 2015–2018. A two-layer shallow-water numerical model proved to be an accurate and reliable tool for computing the salt-wedge dynamics in the Neretva River estuary. The simulations showed that the river inflow has the strongest impact on the salt-wedge dynamics, whereas sea levels and tides have a much smaller effect, mainly related to daily variations of the salt-wedge length and volume. Finally, several simple equations were derived, which link salt-wedge intrusion length, salt-wedge volume, and salt-wedge spread to the river flow rate.