Quantifying the Influence of Sinkholes on Water Balance in Iran’s Golgir Alluvial Plain

Abstract

Abstract. Southwestern Iran's Golgir plain lies on chalky bedrock made up of Tertiary gypsum surrounded and covered by thin Quaternary deposits. Since the onset of the new millennium, this region and its farmland has been prone to land depression and other instability phenomena linked to gypsum dissolution. A simple water balance over the period of 2005 to 2012 was employed to assess the role of sinkholes in these phenomena. Geological and geophysical features as well as initial water balance calculations confirmed the presence of sinkholes and their influence in the study area. A significant discrepancy (2.55×10 6 m 3 ) was observed between annual estimates of water inputs and discharge from the region, likely attributable to errors in identifying and quantifying output components. A bedrock map derived from geophysical investigations and the geological characterization of the chalky bedrock showed that, in comparison to the local groundwater table, there was a roughly 40 m drawdown towards the location of sinkholes. Groundwater inflow towards the aquifer was revised so as to include an identified sinkhole output component in the water balance equation, resulting in a much greater accuracy in the annual water balance estimates. Estimated annual recharge volumes ranged from 4.39×10 6 to 7.15×10 6 m 3 , with a mean of 5.64×10 6 m 3 . The water balance equation was shown to constitute a simple, cost-effective, and reliable approach to the recognition and evaluation of sinkholes in areas under similar conditions.