Jarreh Dam in the southwest of Iran has two specific features that made it almost important to be studied here. The dam is unique in the country for having not any water tightening structures including cutoff wall or grout curtain. On the other hand, almost its entire reservoir is located over the Gachsaran Evaporites of Miocene age with several karstic features. A new type of structural polje bounded by thrust faults is introduced here named as Duz Madui polje. This study is aimed at investigating the geology of Jarreh dam site and reservoir from an applied perspective, with special attention to the karstification in the Gachsaran evaporites and the impact of neotectonics on it, vice versa. The investigation is essentially based on: (1) geological field surveys and aerial and satellite imagery; (2) collection and interpretation of structural data; and (3) analysis of morpho-structural features especially in the Gachsaran Formation. The mutual impacts of the neotectonic structures and Gachsaran Formation on the current and future behavior of the dam is important and debatable. The relationship between neotectonic activity and evaporite karst development can be noteworthy in dam
