Investigation of the phenomenon of subsidence due to the decrease of groundwater level in the city of Urmia using the zoning of changes in the distribution of soil layers

In the present study, the phenomenon of land subsidence in the Urmia plain (west of Lake Urmia) has been investigated. In the study area, 53 observation wells were used to study the changes in groundwater depth. The groundwater depth of the plain varies between 1 and 50 meters and decreases from west to east. In the northwest of the plain in Nooshinshahr lands, the number of isothermal curves is 50 meters, which decreases to the east of the water table depth. Examining the information obtained from periodic subsidence visits, a number of piezometers were observed in the margins of the eastern margin of the Urmia aquifer, which led to the protrusion of the pipe and its fittings. The trend of subsidence at 18 piezometers was studied. Subsidence values in Urmia plain vary from 5 to 17 cm. Most subsidence has occurred in the north and northwest of the plain, which in terms of granulation has a higher percentage of fine sediments. In the area of Chai shrine to Shahrchay, it decreases and reaches 5 cm in Jarchilo well. The amount of subsidence between Shahrchay to Barandozchay Rivers has increased significantly towards Lake Urmia and varies between 6 cm to 13 cm. These changes are due to two main reasons, one is a sharp drop in the water table (uncontrolled withdrawals) and the other is the compaction of fine-grained sediments due to a drop in the water table and a decrease in hydrostatic pressure and weight gain of high sediments.