Use of a maximum entropy model to identify the key factors that influence groundwater availability on the Gonabad Plain, Iran

The purpose of this study is to identify the key factors that influence the availability of groundwater resources in a 10-year period in the Gonabad region of Iran using a maximum entropy model. For this purpose, 165 qanats were selected in 2004 that had yields of more than 3 l/s. By reviewing similar studies, 13 factors were considered to have an influence on groundwater potential exploited by the qanats, including: slope aspect; drainage density; fault density; distance from faults or other fractures; land use; lithology; plan curvature; profile curvature; qanat density; distance from rivers; land slope; stream power index (SPI); and topographic wetness index (TWI). The results indicated that qanat density had the greatest influence on the groundwater potential in a given area. Additionally, the increased importance of this factor with the occurrence of drought indicates that qanats are appropriate structures for exploiting groundwater and that they were well sited when they were originally constructed. Other important factors that influence groundwater potential are SPI, TWI and lithology factors. This indicates the importance of the slope, water accumulation area and rock characteristics in the groundwater potential. Additionally, there were significant changes in the distribution of areas with a high to low groundwater potential over a 10-year period. Reducing the number of effective factors in 2014 modeling showed that with the occurrence of drought and the limitation of areas with groundwater potential, the factors affecting zoning of the groundwater potential are also limited.