Pulvar River changes in the Pasargadae plain (Fars, Iran) during the Holocene and the consequences for water management in the first millennium BCE

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Located in the middle basin of the Pulvar river (Fars, Iran), Pasargadae was founded around 550 BCE in the early days of the Achaemenid Empire. Its territory is dotted with remains of imposing hydraulic facilities (dams, dikes, canals), some of which date to that very period. The purposes and functions of these structures, built to exploit surface water, located in today’s landscape (a deeply incised valley with temporary watercourses), raise questions and problems for which geomorphological studies provide major elements for consideration. Erosion of the Pleistocene glacis by the Pulvar and its tributaries caused several phases of alluvial deposition during the Holocene. They can be seen today in the Pasargadae region by examining the remains of three well-developed steplike terraces. These sedimentary units are primary archives for the reconstruction of river dynamics, and thus allow a better estimation of water availability. Since 2016, within the framework of a joint Iranian-French archaeological mission, several geo-archaeological campaigns have been carried out. Sediment analyses, C-14 dating and OSL dating of sediments collected in the alluvial formations, as well as in archaeological contexts, have been made to accurately reconstruct the variations over time in the Pulvar regime, as well as the past regional waterscape. From the beginning of the Holocene to the onset of the 1st millennium BCE, the Pulvarcatchment area was marked by an aggradation phase, which led to the valley being filled with alluvial deposits. This sedimentary unit provided vast areas of arable land where cultivation could be enhanced by irrigation. The creation of water inlets in the Pulvar and its tributaries was at that time facilitated by riverbeds less incised than present-day ones. Ancient hydraulic systems reflect these geomorphological conditions, since they were built to manage higher water levels, as well as stronger flows, when compared to irrigation facilities developed in modern times