Reservoir-Piezometric Water Level Relationship: Analytical-Numerical Modeling with Field Observations

Monitoring pore water pressure is widely used in water retention systems to evaluate geo-structural performance and to track variations in hydraulic conditions. A common approach for interpreting such data is to examine the relationship between measured pore water pressure head and upstream water levels. However, the implications of the resulting trends are not always well understood. This paper investigates these relationships in detail, aiming to clarify the physical meaning of observed trends and their evolution over time. An analytical solution is first developed for one-dimensional flow paths subjected to a continuously rising upstream water level, and the influence of key parameters on the piezometric pressure response is evaluated. Subsequently, numerical modeling is employed to analyze more complex reservoir level variations and their impact on pore pressure behavior. Building on this theoretical framework, field measurements are examined to demonstrate how different response trends may arise and how they can be interpreted in practice. The results provide insight into the mechanisms governing pore pressure evolution and offer guidance for more informed interpretation of monitoring data in water retention systems. The proposed framework represents a theoretical analytical solution developed for idealized one-dimensional saturated porous media with homogeneous hydraulic properties. Consequently, its primary contribution is to provide physical insight into the mechanisms controlling transient piezometric lag rather than a comprehensive representation of all field conditions.