A significant proportion of the world's deserts is covered by soils characterized by low hydraulic conductivity, high runoff coefficient and high levels of salinity. The groundwater is usually also saline in such regions. It has been proposed to use clayey watersheds for collecting runoff water during seasonal precipitation and infiltrating it into the saline water table, thus creating an artificial lens of fresh groundwater (ALFGW). The National Institute of Deserts, Flora and Fauna of Turkmenistan constructed in the Kara-Kum Desert a pilot system for ALFGW formation (infiltration basin with recharging wells). It was found that over 3-4 years (with a mean annual runoff of 10,000-15,000 m3/km), about 20,000-25,000 m3 of surface water could be infiltrated. This created a lens of maximum 7 m thickness that could be used as a fresh water reservoir. To understand the process associated with ALFGW formation and its pumping, we applied a mathematical model of density driven flow and transport in the unsaturated-saturated zones. The FEFLOW code was used for simulations and the model was calibrated with available field data. It was found that there is a relatively sharp interface between the ALFGW bottom and the saline groundwater, while changes in water salinity are minor within the ALFGW. Simulations of the ALFGW indicated that, with time, a vortex flow develops under the lens edges. This leads to an increase in mixing between the fresh and saline water zones, thus increasing the lens areal extent while decreasing its thickness. The process mainly depends on the hydraulic parameters and the water infiltration regime. Lowering the hydraulic conductivity and the infiltration rate, leads to an increase in the ALFGW; however, increasing the infiltration time raises water losses by evaporation. During pumping of the ALFGW, up-coning of saline water occurs, which depends on the pumping rate, the well screen parameters, well location, and ALFGW characteristics. Using two pumping wells, which are screened in both the fresh and saline water zones, considerably decreases the up-coning effect and the risk of salinization of the freshwater zone. It was found that for sustainable pumping, discharges of wells in fresh and saline water zones is proportional to the transmissivities of these zones.
|Journal||American Geophysical Union, Fall Meeting 2004|
|State||Published - 1 Dec 2004|
- 1829 Groundwater hydrology
- 1831 Groundwater quality
- 1832 Groundwater transport