A novel technique to mitigate saltwater intrusion: freshwater recharge via drainpipe in permeable paleochannel
E. Zancanaro, C. Zoccarato, P. Teatini
Dept. of Civil, Environmental and Architectural Engineering,
University of Padova, Padova, Italy
F. Morari, I. Piccoli, A. Carrera
Dept. of Agronomy, Food, Natural Resources, Animals and Environment, University of Padova, Legnaro, Italy
ABSTRACT
Seawater intrusion (SWI) is threatening coastal aquifers and farmland productivity worldwide.
Although this phenomenon naturally occurs in coastal areas, it is intensified by anthropogenic
activities such as groundwater pumping and land reclamation
that cause a lowering of the hydraulic head and land subsidence. Moreover, the consequences of
climate change such as sea level rise, increase of the mean temperature and the shifting of rainfall
events to tropical regimes, have strong negative effects on
groundwater quality and agriculture. Countermeasures against SWI are needed to maintain agricultural
productivity and protect the freshwater resources in coastal areas. In the low-lying farmlands surrounding
the southern Venice Lagoon, in northern Italy, SWI is exacerbated by land subsidence, the presence of
sandy paleochannels connected to the lagoon subsurface, seawater
encroachment into the river estuaries, the presence of fossil brine waters and peat deposits.
This study provides a detailed hydrogeological and geochemical characterisation of an experimental
agricultural field affected by SWI located in this area using
a large dataset collected over the 4 years between 2019 and 2022. Furthermore, it presents the results
of novel intervention established across the farmland in 2021 to mitigate saltwater contamination.
This intervention involved a controlled discharge of freshwater supplied by a reclamation channel through
a 200 m-long drainpipe buried 1.5 m below the field surface along a well-preserved sandy paleochannel.
The interpretation of the collected data demonstrates that the freshwater recharge carried out in
2021 and 2022 effectively reduced the groundwater salinity along the paleochannel. Moreover,
statistical analyses highlighted that a certain lateral spread of freshwater occurred too, although
the variability of the monitored parameters in the sites located
outside the sandy body was only partially explained by the drain activity.
