Coastal Bris Wetland Hydrodynamics in Non-monsoon and Monsoon Seasons at Mengabang Telipot Terengganu, Peninsular Malaysia

BRIS (beach ridges interspersed with swales) wetlands dominate the coastal plains of the east coast of Peninsular Malaysia. This study examined the impact of rainfall and river levels on groundwater hydrodynamics in a coastal BRIS wetland at Universiti Malaysia Terengganu during the northeast monsoon and non-monsoon seasons (July 2022 to January 2023). Six monitoring wells (WA-WF) were built, with WB, WC and WD positioned on the higher ground, whereas WA, WE and WF were on the lower ground. River levels were observed at three stations (R1–R3), rainfall data were collected using a weather station and tidal data were obtained from an existing station. Measurements at 5-minute intervals identified a strong correlation. Between tidal oscillations and river water level (r = 0.7–0.92, average, 0.81), typical of tidal rivers. However, the influence of tidal oscillation on groundwater level was weak (average r = 0.22), suggesting an indirect influence through river dynamics. Groundwater level in lower areas near rivers was more influenced by river water level changes (average r = 0.54, monsoon average = 0.76). In contrast, the higher section showed a weak influence in general (average r = 0.02, monsoon average = 0.34). During monsoon season, increased upstream flows elevated river levels, enhancing hydraulic connectivity across the wetland. Groundwater fluctuations were limited to 0.5 m below ground, with lower areas frequently saturated or inundated, limiting floodwater retention capacity. Future research could explore the impact of soil texture and porosity to refine understanding of BRIS wetland hydrodynamics.