An investigation of changing river courses during the Holocene in the Lower Khuzestan plain (SW Iran): a contribution to archaeological and historical studies

An investigation using sedimentological characteristics of subsurface records documents the nature and changes of the rivers Kupal and Jarrahi (SW Iran), and their associated alluvial plains during the Holocene. Today, only traces of the Kupal river, located in between the rivers Karun and Jarrahi, are present. The sedimentary data, however, demonstrate that the Kupal river did exist and was connected with the Karun river. The relocation of the Karun river towards the west during the late Holocene had a significant impact on the hydrological conditions of the Kupal's alluvial plain, initially transforming it into a poorly drained area. After 2700 - 2350 yr cal BP (ca. 750 - 400 BCE) drainage conditions improved, probably by a second avulsion of the Karun river towards the south whereby a new outlet was created for the Kupal river. An alternative hypothesis is that a change in water management practice in the distal part of the Khuzestan plain may have improved the drainage conditions in the proximal part. The Jarrahi river also bears a history of changes. Until at least around 2010 - 1870 yr cal BP (ca. 60 BCE - 80 AD) the river flowed south to discharge into the Persian Gulf. The river's alluvial plain was isolated from the western part of the Lower Khuzestan plain because of the presence of a ridge forming an interfluve between the alluvial plains of the Jarrahi river in the east and those of the rivers Kupal and Karun in the west. An avulsion led to the abandonment of the southern connection with the Persian Gulf and was the start of the switch to its present position. This new course is marked by abrupt changes in flow direction; first to the NW and then to the SW. These changes were facilitated by the disappearance of the interfluve that became buried by aggradation in the late Holocene, and the lower position of the alluvial plain of the Kupal river in relation to the altitude of the plain of the Jarrahi river. The characteristics and interpretation of the sediment records suggest that the current ideas about the late Holocene geomorphological evolution of the study area from former publications require revision.