Investigating the geological potential of the Birjand area for establishing and extending flood farms (Bandsar)

Khorasan Province is one of the areas in which it is not possible to cultivate farmlands because of low rainfall, and hence, flood farms (bandsar in local dialect) are considered an effective traditional method for flood cultivation in the region. We used a geological map of Birjand at a scale of 1: 250,000 to select the study area. This area includes the city of Birjand and numerous population centers such as Sarbisheh, Dastgerd, Hajiabad, Morak, Naferest, Giv, Mazhan, Khosf, Berming, Sarchah Shour, and Sahl Abad. In this research, based on the diversity of geological formations, the degrees of erodibility and the type of sediment load produced by each rock unit were determined. Then, appropriate areas for the development of bandars were located based on the quantitative and qualitative role of geological formations. Based on the processing of Google Earth images from the study area, the area covered by bandsars in ​​the region was calculated to be 24,000 hectares. The plains and alluvial fans of the region, which are potential locations to develop flood farms, are estimated at 658222.2 hectares, covering about 42.07% of the total area. By comparing these figures, it is estimated that only 3.65% of alluvial fans and plains in the region have been under construction and utilization for bandsars. The rock units were classified into appropriate, semi-appropriate, inappropriate and very inappropriate based on the severity of erodibility and the type of sediment load produced. Based on the results, it can be concluded that more than 75% of the formations in the upstream areas have poor potential and only 25% of the remaining districts have the potential for establishment of bandsars. Therefore, considering geology and other factors such as slope and occurrence of flood waters, it is necessary to take comprehensive measures to determine areas suitable for development of bandsars.