Influence of lakebed sediment deposit on the interaction of hypersaline lake and groundwater: A simplified case of lake Urmia, Iran

Lake Urmia, which was once the second-largest saline lake in the world, has been shrinking dramatically. Moreover, Lake Urmia has become supersaturated with total salinity averaging more than 350 g/l. Salt precipitation and dissolved materials brought by inflowing rivers have formed a layer of sediment with low hydraulic conductivity on the lakebed. Considering the flat bathymetry of Lake Urmia, we conducted a series of numerical simulation scenarios to study the groundwater flow pattern in the vicinity of the hypersaline Lake Urmia using COMSOL Multiphysics®. In the first step, we performed the simulations in steady-state conditions. Secondly, we simulated the lake level fall in 10 years at a rate of −35 cm/year followed by a lake level rise at a rate of 35 cm/year for another 10 years. The steady-state results demonstrate that decreasing sediment hydraulic conductivity layer and increasing its thickness lead to a less intense saltwater intrusion, with lower saltwater flux from the lake to the aquifer. As the lake level begins to fall, in cases with high sediment hydraulic conductivity, incoming saltwater from the lake decreases and reaches nearly zero values through the time; instead, the lake begins to get recharged. On the other hand, as the lake level begins to rise after the falling period, the saltwater flux from the lake to the aquifer increases and finally reaches a value of nearly two times greater than steady-state results. In low sediment hydraulic conductivity cases, incoming saltwater from the lake to the aquifer remains negligible through both rising and falling scenarios.