Trend analysis of annual, seasonal and monthly groundwater level (Case study: sub-basin of Arak Mighan)

In the present study, the Miqan sub-basin of the Arak region was quantitatively investigated to find out the temporal and spatial variations of groundwater level in the nine Qanats (subterranean canals).  The methodology to evaluate the spatial and temporal changes of groundwater level,  the  26 years data of changes in underground water (1365 -1390) produced by the Water Authority Bureau of Arak city for the Miqan-sub-catchment were collected and analyzed using GIS software and time series methodology processing of data. In this methodology, firstly the mean of water discharge and withdrawals of qanats water for daily, monthly and annually were analyzed and monitored.  Then the trend of changes in the water level of all investigated wells for the 26 years data was graphically determined for those time series respectively. Secondly, a group of hydrograph for this sub-catchment were presented in figures and compared for all-time series based on daily, monthly, seasonally and annually respectively mentioned in the paper. Linear regression (simple linear) and Mann-Kendall statistics method were used to test the significant trend of changes in the underground level for all the periods' mentioned above. In the last stage, to produce the sub-catchment maps for showing the groundwater hydrograph of the plain, interpolation on maps was performed using ARC GIS software. The results indicated that according to the hydrograph of the 26 years of groundwater level has decreased drastically. Available hydrogeological data also show a sharp drop in aquifer water levels in recent years. The maximum rate of decline has been observed in the central parts, located below the Miqan basin. The most important reasons in increasing the rate of groundwater level are the mismanagement and uncontrolled withdrawal of groundwater resources by resident farmers and also the frequent reduction of precipitation