H. Haghnazar - Faculty of Civil Engineering, Shahrood University of Technology, Shahrood, Iran
B. Hashemzadeh Ansar - Department of Civil Engineering, Shomal University, Amol, Iran
R. Amini - Faculty of Civil Engineering, Shahrood University of Technology, Shahrood, Iran
M. Saneie - Soil Conservation and Watershed Management Research Institute, Agricultural Research, Education, and Extension Organization (AREEO), Tehran, Iran

River bed sand and gravel are utilized more than mountain materials due to their availability and closeness to the transit roads and sites of usage. Excessive and non-technical extraction of gravel and sand bring a kind of interference in them, leading to many negative consequences. Therefore, presenting solutions to reduce these impacts and infilling mining pits are essential. In this research work, through an experimental work, locating two consequent river bed mining pits in the form of the distance between them and also their distance from the walls for the purpose of infilling and extraction management was investigated. The results obtained showed that movement of the downstream pit did not significantly affect the infilling volume and migration of the upstream pit but by movement of the pit towards the wall, the infilling volume of the upstream pit was reduced by up to 25% compared to the channel center. Concerning the downstream pit, the impact of the distance between pits depended on their distance from the wall so that if the pit was close to the channel center, the infilling volume was increased, and if it was located close to the wall, the infilling volume was increased up to a distance equal to 9 times the flow depth, and after that the infilling was reduced. In case the pits were excavated towards the channel center and the downstream pit was excavated at a distance equal to 12 times the flow depth, the best state of infilling and pit migration did occur.

Material Extraction, Mining Pit, Sediment Transport, Migration Velocity