The seasonal variation in the level of the river influences the quantity of water that these dams can contain. In this study, the effect of changing the water level of the river on the stability and performance of a filtration system at a small earth dam is evaluated for a period of 10 years. The article discusses the influence of alternate droughts and heavy rain periods on dam water storage and highlights that hydraulic conductivity is not constant, as is usually considered in leakage studies. Specifically, the study focuses on the Al-Wand Earth Dam. The study analyzed the daily water pressure data from 2015 to 2025 using GeoStudio (SEEP/W). The research was carried out in four steps: data gathering, computer modelling, seasonal decomposition, and validation calculations. This process showed considerable differences between the theoretical assumption of continuous permeability and the actual situation in the field. Thus, a hydraulic analysis was carried out and divided into two seasonal models: winter/filling and summer/low water level. The results showed remarkable long-term accuracy with cumulative Nash-Sutcliffe efficiency values of 98 % for the winter model and 95 % for the summer model. Importantly, the study observed that the effective permeability at summer low water levels reduced by nearly 88% relative to the design values, a substantial departure from the safety limits.