Groundwater and Solute Budget (A Case Study from Sabkha Matti, Saudi Arabia)

Sabkha Matti is the largest inland sabkha (2950 km2) in the Arabian Peninsula. The drainage area supporting this sabkha is >250,000 km2 and is the discharge point for part of the ten thousand meter thick regional groundwater systems ranging in age from Precambrian through Miocene in the Rub’ al Khali structural basin. A hydrologic budget was constructed for this sabkha, where water fluxes were calculated on the basis of hydraulic gradient and conductivities measured in both shallow and deep wells. The evaporation rates from the surface of the sabkha were estimated from the published data and indicate that almost all the annual rainfall is lost by surface evaporation. The water flux multiplied by its solute concentration showed that nearly all the solutes in the sabkha were derived by upward leakage from the underlying regional aquifers rather than the weathering of the aquifer framework, from precipitation, or from other sources. Steady-state estimates within a rectilinear control volume of the sabkha indicate that about 1 m3/year of water enters by lateral groundwater flow, 2 m3/year of water exits by lateral groundwater flow, 20 m3/year enters by upward leakage, 780 m3/year enters by recharge from rainfall, and 780 m3/year is lost by evaporation. The proposed conceptual model of the hydrology for sabkha Matti is assumed to apply to the rest of the inland sabkhas of the Arabia Peninsula and to many ancient environments of deposition observed in the geologic record.