factors affecting the qajar-era fort settlements in iran's sistan region due to hydrographic changes in the hirmand river

Locating fort settlements in iran's sistan region during different historical periods have always been associated with changes in the direction of hirmand river which often occurred due to various natural and human factors. one of the most important determining factors in locating the aforementioned settlements is changes in hydrographic network. this study aims to identify the relation between the iranian province of sistan hydrographic networks and the fort settlement during the qajar era. the research method applied, here, is descriptive-analytical, historicalcomparative, documentary, library and the field study in iran's sistan area. the main focus of the study is on the issue of changes in the hydrographic network of the hirmand river. the main question is to what extent have the changes in the direction of the hydrographic network of hirmand played a role in locating fort settlements of the 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 during qajar are related to the hydrographic basin of the sistanriver. the main reason is branching of the hirmand river's 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, there have been settlement areas. however, in the qajar era, 100 percent of the settlements in the northern delta area have been site selected.