Karstic features in gypsum of Gachsaran Formation (case study; Chamshir Dam reservoir, Iran)

Abstract

Chamshir Dam site is located in southwest of Iran, on Zuhreh River, 20 km southeast of Gachsaran city. The study area mainly covered by evaporite formations of Fars Group especially Gachsaran Formation. Dam axis is located on limestone beds of Mishan Formation but nearly two-thirds of the dam reservoir is in contact with the Gachsaran Formation. The reservoir and dam site have been brecciated by several faults such as Dezh Soleyman thrust and Chamshir fault zone that lead to development of karst in this region. The region has a wide variety of developed karstic features such as karrens, dissolution dolines, karstic springs and cavities. These karst features can compromise on the ability of Chamshir Dam to hold water in the reservoir, and can even cause collapse of the dam. Gypsum karst in the Chamshir Dam reservoir may develop the solution channels and cavities which cause water to flow toward downstream of the dam reservoir. Therefore, to eliminate these problems, construction of cutoff wall or clay blanket is proposed.