Investigating of quantitative trend changes in Aquifer water table during1992 -2011 by Mann-kendall test (Case study: Firoozabad plain, Fars province, Iran)

Groundwater in arid and semi-arid areas is one of the important sources for various uses that undergo quantitative changes. One of these areas is Firoozabad plain in the west of Fars province, whose groundwater is the main source of agricultural and drinking water. In this paper ,quantitative change in groundwater level of Firoozabad plain, which is one of the agricultural  hubs of iran,were investigated by Mann-Kendal l test.The result showed that  according to the unit hydrograph of Firoozabad plain in the statistical period of !992-2011in the east and west of the river, the general trend of water table changes has a continuous ang significant decline,so that in the east of the plain more than 21  Meters and in the west 20.83meters the groundwater level has dropped. However, due to heavy rainfall(678mm) in 2004, the map of groundwater depth changes in the aquifer in 2001-2006shows less decline. Changes in the unit hydrograph of Firoozabad plain for the period 2006-2011 show a sharp drop in groundwater level, so that it can be seen in everywhere of aquifer drop.Groundwater balance of the aquifer of this plain in the statistical period indicate that the change in the volume  of the  aquifer reserve due to additional harvest(discharge) during the statistical period of 17.5million cubic meters is negative anf is the main cause of water table decline.This discharge was mainly provided by exploitation wells.Due to the role of surrounding geological formations in feeding the aquifer of Firoozabad plain,it is not possible to use this resource to compensate for water shortage in the future. Therefore, other water resources in the region, including water transfer from Tangab and Hayqar dams, should be considered. In general, in the margins of the heights, the water source depth decreases more and decreases towards the center of the plain.