Seepage and Pore Pressure Response to Reservoir Level Fluctuations during the Impounding Phase of Karian Dam

Seepage-induced internal erosion and piping account for approximately 43% of embankment dam failures globally, with risk significantly elevated during the initial impounding phase when rapid reservoir level rise amplifies hydraulic gradient in the foundation. This hazard is particularly critical for dams with halloysite-rich clay cores constructed over pyroclastic rocks such as lapilli tuff, where the combination of high plasticity and heterogeneous permeability creates complex seepage pathways and delayed pore pressure response. This research aims to evaluate the seepage and pore water pressure responses to reservoir water level fluctuations during the initial impounding of Karian Dam (September 2023–May 2025) using 10 vibrating-wire piezometers and 1 V-notch weir for comprehensive field data collection. Data were analyzed with rigorous preprocessing to eliminate rainfall effects and isolate dam-driven seepage. Linear regression revealed a strong relationship between increasing reservoir elevation and seepage discharge: y = 0.2259x − 7.054 (R² = 0.9089), with seepage increasing from 3.3 l/s (elevation 46 m) to 8.3 l/s (elevation 67.97 m). Maximum Seepage Index 0.084 at elevation 70.85 m remained well below the safety threshold (QI < 1.0), confirming controlled piping risk. Upstream pore pressure substantially exceeded downstream values, indicating effective core hydraulic dissipation. The phreatic surface remained entirely within the dam body, confirming appropriate initial design. Integration of systematic multi-instrument monitoring, real-time regression analysis, and Seepage Index evaluation during the early filling phase represents a methodological advancement in Indonesian dam monitoring and supports the development of SCADA-based early detection systems for dam safety management in Indonesia.