Extended Abstract
Introduction: In arid and low rainfall regions where evaporation is high due to special climatic conditions, the possibility of surface storage of waters in many cases, on a small scale, is difficult and uneconomic because part of the water is out of reach due to evaporation and the other part of the water is out of reach due to infiltration. Also, many surface reservoirs do not have a long shelf life and are filled and out of reach due to accumulation of sediments. Therefore, underground dam studies are very important. One of the new technologies used in the field of groundwater development is the underground dam, which is used for various purposes such as preventing the movement of saline waters in desert. Underground dams are compatible with environmental conditions.
Materials and Methods: To do this research, the watershed of The Rayen Underground Dam in the south of The City of Rayen and southeast of Karman city was selected. Geoelectric studies of the underground dam in The Reyen area were carried out in several stages with a total of 35 electric sondages. After harvesting the data and processing them by IPI2win software, the information of each of the harvest points in the region has been determined. The type of used geoelectric method is the harvesting method of four electrodes with Schlumberger array. 
Results and discussion: The importance of underground dams has been considered by most researchers around the world in recent years, and new types of methods are also used for their detailed studies, among which is the use of geoelectric method for studying underground dams. This has been considered in this research. Also, according to geological studies of Rayen region and geoelectric and topographic samples of the region, it can be concluded that the studied section is confined to two rock extrusions with the genus rhyolite and pyroclastic. Also, subsurface information of geoelectric sodages indicates the persistence of volcanic Igneous Stone below the intermediate surface between the two mentioned rock extrusions at a depth of 8 to 14 meters above the river bed surface and the slope of the bedrock from the sides to the center of the cross section in such a way that the maximum depth is in the center of the river and the minimum depth of bedrock is in the vicinity of rock extrusions. Considering the high importance of underground dams, it is suggested that the geoelectric studied methods in this study be studied more and more accurately to study underground dams in different watersheds throughout the country.
Conclusion: The results showed that the specific electrical resistance of the bedrock increases from upstream to the proposed axis. This indicates the change of bedrock in close range to the proposed axis compared to the upstream points. However, the specific resistance values related to alluvial layer in the whole study area do not change much and this state indicates the uniformity of alluvial layer in the study period. The specific resistance values of the bedrock are generally higher than the specific amounts of alluvial layer and the alluvial layer shows low specific resistance due to its abundant salts and brackish water. In addition, the specific resistance range of sediments and rocks showed a total of at least 36 ohms -meters and a maximum of 1313 ohms- meters.