The level of safety of small earth dams, operating without staff and measurement and control equipment, are considered in this study. Approach enabling the possibility to define the finite lifetime (Tf) of a small earth dam here presented. The proposed approach does not require any variables monitoring. It is based on the definition of Tf by assessing the water impact on the small earth dams by quantitative methods of system analysis. To assess the earth dam Tf, two approaches are offered, which based on the digraph method. They are the classification scale construction and the cluster method. On a quantitative base the Tf of small dam on urban area can be defined as the minimum between the two (75 year for the classification scale and 80 for the clustering), which is however well above the Russian regulations, which indicate a period of 50 years (design life). The estimated value allows defining robustness of earth dam and can be used as a criterion for safety management of earth dams, defining the needs to undertake actions to improve, during the life cycle, earth dam structural features.