2D Electrical Resistivity Tomography for the Investigation of the Subsurface Structures at the Shaqlawa Proposed Dam Site at Erbil Governorate, NE Iraq

Two dimensional Electrical Resistivity Tomography (ERT) method was used to investigate a Dam site in Shaqlawa-Erbil Governorate, NE Iraq, to delineate the nature of the subsurface structures to assess its suitability for the construction of dam. The main objectives are to investigate the depth to the bedrock, possible geologic structures, such as possible presence of faults, fractures, voids and clay in the dam axis and abutments. The selected method has the possibility to give an image of the subsurface and map lateral and vertical variations in the subsurface geology of the site. For this purpose, the (SYSCAL Switch and SYSCAL Pro Switch units) equipment was used with Wenner array (48 electrodes). Three 2D electrical resistivity tomography profiles were conducted, the space between electrodes is 5m and the length of the profiles are 235 m. The depth of the investigation is assumed to be 40 m. The acquired data were inverted to tomogram sections using tomographic inversion by using TomoLAB commercial software. The Tomography sections show that the subsurface is classified into three distinct geo-electric layers, with different resistivity values, starting with high to moderate resistivity value represents unconsolidated coarse materials such as boulder and gravel, while in some location fine soft materials such as silty clay has been appeared that is underlain by a second layer of high resistivity has been detected within upper Fars (Injana) Formation, it is mainly composed of sandstone saturated and/or compacted. The third layer has low resistivity which represents the fine materials deposition of the Upper Fars Formation. These results are confirmed and verified by using several boreholes data were drilled on the recommendation of the surveys. The results showed that the site is suitable for the construction of the proposed dam.