This study estimates the recharge dynamics in an unconfined porous coastal aquifer by means of a time-series approach. Two water wells were selected in the Volturno Plain (Campania Region, southern Italy), respectively located in a wetland area close to the coastline (Pz1) and in an agricultural not irrigated field at 10 km inland close to the Volturno River (Pz2). A multiparameter probe was installed in each water well to measure: water depth, temperature and electrical conductivity. Data were collected every 24 hours from February 2016 to December 2017 in Pz1, and every 12 hours from October 2022 to the present in Pz2. Rainfall data collected at the meteorological station closest to each monitoring point were considered in the analysis. The recharge rate was estimated using the Water Table Fluctuation (WTF) method. Six and five single recharge events were identified at Pz1 and Pz2, respectively.
At Pz1, the recharge ratio (RR, ratio between recharge amount and precipitation amount) remains constant throughout the year (average RR = 45%), likely due to the presence of marshy land, which limits groundwater recharge during heavy rainfall. At Pz2, RR shows seasonal variations with average values of 104% in autumn-winter and 351% in spring-summer, probably related to the agricultural practises (bare land, planting, growing and harvest phases). The results indicate that recharge decreases as precipitation increases due to greater pore saturation during the infiltration process. In both sites, we observe that precipitation events exceeding 50 mm in 24 hours result in a decrease in both electrical conductivity and temperature, highlighting the influence of infiltration dynamics on groundwater chemistry. Lastly, recharge amounts calculated using the WTF method are compared with those obtained through a classical hydrogeological balance, showing a good correlation.
This study highlights how groundwater recharge varies in response to seasonal changes and soil conditions.