Environmental Hazards Role in Achaemenid Settlements Placement in the Sistan Plain in the Hirmand River Basin

The Sistan Plain for a long time has faced hazards of flood, drought and sandstorm. Also due to existence of abundant water resources it had been one of the important places for men’s placement. So far, no comprehensive study has been done on environmental hazards which would include ways to overcome or decrease their impacts in Achaemenid era. The present survey aims for studying the reciprocal relation between Achaemenid settlements and natural environment in areas based on environmental limitations. This research has been carried out through the descriptive- analytical- historical method using GIS software. After environmental conditions had been studied, variables types and distance from water resources, slope, soil type, Geology and wind were studied and the results indicate surface water resources effective role in settlements placement. The Water resources existence, gentle slope and consequently ease of waterflow down to plain and canals creation capacity to keep suitable distance to river and placement on Alluvial terrace to avoid flood hazards are among the factors turned area to population absorbing one despite shortage of aquifers and reliance on surface water resources. Being located on delta fans would lead to change of the direction of river canals, which causes relocations of settlements.