Geochemical modeling of a small hypersaline watershed was done based on runoff geochemical evolution study. After validation, this model may represent the regionalsystem. The study investigated the Lower Jordan River Valley, which is a part of the Dead Sea Rift. Runoff is generated by precipitation along mountain rims (>1000 m above the valley) and by rains within the valley. The drainage pattern is mainly from the highlands that delineate the region of study on the east and west, to the Jordan River-Dead Sea system, and through it south to the Dead Sea. Along the valley several intermediate basins were found, the most pronounced being the Mallaha salt marsh system. This local depression probably evolved through halokinetic geomorphlogy, which is noticed also by geochemical aspects. Runoff Total Dissolved Salts (TDS) increases relative to that of rainwater by up to two orders of magnitude. This is mainly due to dissolution of salts from soil crusts. The saline runoff is usually of the Na+-chloride type with a Na+/Cl- ratio that is slightly lower than the oceanic value. Cl-/Br- ratios are lower than those expected from halite dissolution indicating that salinity increase might involve a repetitive dissolution of soluble salts other than halite. Runoff δ18O vs. δD values are scattered along a local evaporation line, which was calculated for rainwater that was sampled in the Lower Jordan Valley (LJV). It seems that the extremely saline nature of the sediments within the valley causes increase in salinity of fresh runoff and also of groundwater. These processes salinize a significant volume of fresh water that otherwise could have been used for various purposes.