Abstract

The study analyzes groundwater level fluctuations in the upper Pleistocene aquifer (qp₃) at well VT8A, Vung Tau City, from July 2020 to November 2023, to assess the impact of rainfall and tidal levels on the aquifer’s self-regulatory characteristics. Rainfall, tidal, and groundwater data were converted to daily values and processed using the Interquartile Range (IQR) method and linear interpolation. Analytical methods included Pearson correlation, linear regression, cross-correlation function (CCF), Granger causality test, autocorrelation function (ACF/PACF) analysis, and stationarity tests using the Augmented Dickey-Fuller (ADF) test. Results indicate average rainfall of 4.18 mm/day, concentrated in the rainy season, with groundwater levels varying widely from -109.2 cm to 82.86 cm (mean -5.83 cm), indicating pronounced, asymmetric variability. Tidal levels were more stable, ranging from 214.83 cm to 340.46 cm (mean 274.45 cm), with uniform amplitude. The correlation between groundwater levels and rainfall was negligible (r = -0.0188, p = 0.5165), suggesting limited direct impact from rainfall, possibly due to the Holocene cover or prolonged infiltration lag. Conversely, tidal levels showed a weak but statistically significant correlation (r = 0.0692, p = 0.0155), reflecting notable tidal influence, particularly short-term fluctuations, aligned with the qp₃ aquifer’s hydraulic connectivity to the sea. CCF and Granger analyses indicate rainfall affects groundwater levels after 2–5 days, while tidal levels exert immediate and sustained effects lasting 1–5 days, highlighting the aquifer’s slow infiltration response to rainfall and strong hydraulic linkage with the sea. Autocorrelation analysis reveals groundwater levels strongly depend on values from 1–2 days earlier (ACF lag 1 = 0.491, lag 2 = 0.26), demonstrating self-regulating ability. The study provides scientific evidence for water resource management and adaptation to climate change in coastal areas.