Zoning of changes in the decreasing groundwater table and temporal monitoring of drought in the Ghorove-Dehgolan plain

The lack of surface water resources has caused the indiscriminate extraction of groundwater in many parts of the world. The sharp drop in the level of groundwater tables, and the investigation of changes in groundwater resources are very important in the planning and sustainable management of water resources in each region. The purpose of this research is to investigate the changes in the level of the groundwater table Ghorveh-Dehgolan plain, which is one of the most important and largest plains of the province. To this end, the statistics of 104 observation wells during three time periods (2001-2008, 2008-2013, and 2013-2018) were analyzed. At first, statistical data was collected, and after entering the data into the Geographical Information System (GIS) with the interpolation method, maps of lines of equal depth, and zoning of decreasing the level of groundwater table were prepared. To investigate the long-term changes and fluctuations of the groundwater level, the representative water table of the aquifer was also drawn in the Excel software. The results obtained from the maps of the same area of the fall showed that the highest level of groundwater in the third time period (2013-2018) in the southern part of the aquifer was 7.3 m, in the second time period (2008-2013) in the central part of the aquifer has dropped by 5.7 m, and in the first period (2008-2001) in the northern and central parts has dropped by 3.3 m. The hydrographs of the groundwater level show that the water level has decreased by 13.8 m in the 20-year period, and the average water level has decreased by 0.7 m every year. The results of the reservoir volume changes showed that the volume deficit of the alluvial reservoir is equal to 56.2 million m3. In addition, the temporal monitoring of drought of the groundwater resources of Ghorveh-Dehgolan plain with the Groundwater Resource Index (GRI) has a downward trend towards drought during the 20-year statistical period.