SUMMARY
This study examines the phenomenon of infiltration of lake water into the rock of the banks of the Foum El Gherza dam. Several companions of measurements and investigations have been carried out on the site of the dam since 1998. Archives and data of more than half-century concerning the problem of the infiltrations were put at our disposal by the national agency of the dams and transfers (NADT). The results obtained showed that the dam was carried out on a cracked karstic site which is therefore permeable. In addition, the stratification of the layers of limestone is deposited with a slope of 30 ° in the direction of flow. Despite the realization of a sealing web at the beginning of the commissioning of the dam did not solve the problem, since the leaks did not decrease in time. During the period: 1950-2017, a volume of 220 million m3 was lost in the stream downstream of the dam. Even if this quantity of water has been recovered and has been used in irrigation the stability of the structure remains a concern for the hydraulic services.