Hydrogeological framework and groundwater modeling of the Sujas Basin, Zanjan Province, Iran

Due to overdraft conditions appearing in most of Iran, management strategies are gaining importance in groundwater studies. Although regional geologic, tectonic and geophysical investigations of the Sujas basin in northwestern Iran have been carried out by the Geological Survey of Iran and water organizations, no conceptual or mathematical modeling of the hydrogeology of the area has been conducted. In this study, detailed local geological, geophysical and hydrogeological investigations were carried out to delineate the architecture of different subsurface geological horizons using lithologs and vertical electrical sounding data. The geological and geoelectrical studies have revealed the existence of a deeper aquifer overlain by relatively impermeable Pleistocene beds of considerable thickness in the eastern part of the basin. To describe groundwater behavior and predict effects of management strategies, a three-dimensional, numerical model of groundwater flow in the Sujas aquifer was developed. Modeled water levels were most sensitive to the recharge rate, the horizontal hydraulic conductivity and the bottom layers. Observed water-level fluctuations were reproduced in some areas but not in other areas. Differences may be due to the influence of local-scale conditions not represented in the regional model or errors in parameterization of the aquifer data.