Chapter 10.7 - Case Study: Springs of the Zagros mountain range (Iran and Iraq)

Abstract

The Zagros Mountain range represents the southern, Asian branch of the Alpine geosynclines. Most of the Zagros Mountains are in the western and southern part of the Iranian territory. There are two main groups of karstic aquifers. The first one belongs to the carbonate rocks deposited during earlier sedimentation cycles. In Iran, it is known as the Sarvak formation, a subgroup of Bangestan of the Cretaceous age, which has a great extension within northern and central Zagros. Its Iraqi equivalent is the Bekhme karstic aquifer, formed of sediments accumulated during the late Lower Cretaceous phase as well as during the lower and middle part of the Upper Cretaceous. The anticlines were divided into two main groups based on the presence or absence of the hydraulic connectivity between the limbs. The geological and tectonic settings are the main controlling factors within these two groups. Each group was further classified into four subgroups based on the location of the discharging zones, namely, one or both down-plunge noses, limbs, traversing river and combination of downplunges, limbs, and river. The factor that directly reflects the regime of karstic aquifers in the area is related to the high variability in terms of time, area, and quantitative distribution of recharge. Therefore, during a recession period, the spring hydrographs display typical monotone depletion of the accumulated resources. The underground drainage development depends on many factors but mostly on effective porosity, the base of karstification, and accumulated nonrenewable groundwater reserves. Therefore, while many springs drastically reduce their yield, others slowly discharge by slightly reducing their spring flow during recession periods.