A 3D density-dependent model for assessment and optimization of water management policy in a coastal carbonate aquifer exploited for water supply and fish farming

- A coastal carbonate aquifer was overexploited for fish farms and domestic use purposes.
- A 3D density-dependent model was developed for simulating the impact of fish farming.
- The model was used to forecast the evolution of resources over time under exploitation scenarios.
- The sustainable management of the aquifer mostly depends on withdrawals for domestic use.
- The water extracted by fish farms significantly affects the freshwater/saltwater interface.

SummaryThe Ansedonia promontory (southern Tuscany, Italy) is characterized by the presence of fish farms that pump thermal saline groundwater. The water is extracted from a carbonate aquifer with high permeability due to fracturing and karstification that is also exploited for irrigation purposes and domestic use. Such exploitation has led to the degradation of groundwater quality, producing conflict among the different users. The conceptualization of the aquifer allowed the development of a 3D finite element density-dependent numerical model using the FEFLOW code. The slightly negative freshwater budget in the very humid hydrologic year of 2004-2005 revealed that the aquifer was overexploited, especially due to the extraction of freshwater (along with seawater) from fish farm wells and pumping from public supply wells. The model was also used to forecast the quantitative and qualitative evolution of resources over time, thus testing the effects of different management hypotheses. Results demonstrate that the sustainable management of the aquifer mostly depends on withdrawals from public supply wells; the quantity extracted by fish farms only significantly affects the freshwater/saltwater interface and, locally, the salinity of groundwater. Actions to counteract seawater intrusion are proposed.