Investigation the factors affecting the groundwater drawdown in Mehran Plain, Ilam

Groundwater resources management has a special importance in the arid and semi-arid regions. Natural and anthropogenic factors caused critical condition and groundwater drawdown in recent decades all over the country including Mehran plain, Ilam province. The purpose of this study was to investigate the factors influencing the decline of water table in the Mehran Plain. To this end, the water levels of 23 wells were used in the area over a period of 20 years (1995-2015). After analyzing the data using ArcGIS software through Ordinary Kriging method, water table drawdown map was prepared. The groundwater unit hydrograph was obtained for the plain. The results showed that the groundwater levels decreased in the area. The Iso- drawdown map also showed that water level of the aquifer decreased between 1 to 32 meters in different parts of the plain and the district with more decline of water table coincided with the area in which the pumping wells had been concentrated. Groundwater Hydrograph also showed that the water table was dropped 16.2 meters during 18 years at a rate of 90 cm per year. The increase of groundwater exploitation and the impact of successive droughts and consequently the decrease in aquifer recharge were the main factors affecting groundwater drawdown in Mehran Plain.