Evaluation of Qanat Subsidence Potential Map in West of Mashhad City NE of Iran

Qanat systems (underground water galleries, kariz) have been used for extracting groundwater in many parts of Iran over centuries. There are 63 Qanat suits in Mashhad city (NE of Iran). In the past, these Qanats were used for extraction of groundwater; however, most of them have dried out today. Cases of land subsidence have been reported due to the collapse of these Qanats in Urban areas. In this paper, the Qanats in the western part of Mashhad city has been studied. The exact locations of Qanats vertical shafts has been determined by aerial photographs with scale of 1:20000 and 1:6000. Qanat characteristics include depth of Qanat underground tunnel and vertical shaft`s diameter has been investigated. The signifi cant factors in Qanats collapse phenomena are soil properties, groundwater table, loadings due to the surface structures, density of vertical shafts and Qanat depth. In this study using of Qanat characteristics and loadings due to the surface structures, a potential map of Qanat collapse hazard and subsidence is presented. According to the fi eld study, several cases of subsidence were recognized in high potential zone that introduced in the potential map.