Factors Affecting the Qajar-Era Fort Settlements in Iran's Sistan Region Due to Hydrographic Changes in the Hirmand River

Locating fort settlements in Sistan region, Iran, during different historical periods have always been associated with changes in the direction of Hirmand River which have occurred due to various natural and human factors. This study aims to identify the relation between the Iranian province of Sistan hydrographic networks of fort settlement in the Qajar era. The research method is descriptive - analytical, historical – comparative, documentary, library and field study in Iran's Sistan area. Our focus is mostly on the issue of changes in hydrographic network of Hirmand River. The main question is to what extent have the changes in the direction of hydrographic network of Hirmand played a role in locating fort settlements of Qajar era in Iran's Sistan region. Records, documents, data and historical information related to the Qajar era were collected and comprehensively compared and analyzed regarding the current and the past situations in the Geographic information system (GIS) using ArcGIS software. The results show that the highest number of the locating and the density of fort settlements in the Qajar era are related to the hydrographic basin of Sistan river. The main reason is branching of the Hirmand River Hydrographic Basin through the Sistan canal or Sistan River in the West. Also from 6 to 12 AH in both the northern and southern Delta region of Sistan, Iran, there have been settlement areas. However in Qajar era 100 percent of settlements in the northern Delta area have been site selected.