Clay Translocation in the Artificial Recharge of a Groundwater System in the Southern Zagros Mountains, Iran

Abstract

The shortage of water in Iran and most countries in the arid and semiarid zones is approaching the critical stage. Because about 60% of the water used in Iran is supplied by underground resources and natural recharge cannot replace the amount of water exploited, artificial recharge of groundwater (ARG) is actively pursued in this country. Desiltation of turbid floodwaters in sedimentation basins is a prerequisite for ARG. It is executed close to the heads of alluvial fans on an extensive area in Iran. Because the sediment removal efficiency of sedimentation basins is not 100%, downward migration of some clay particles, both in sedimentation basins and recharge ponds, causes the gradual impermeability and eventual clogging of the vadose zone and reduces the economic life of the recharge systems. Coarse-grained alluvium beneath 2 sedimentation basins, one in operation for 13 years and the other for 11 years, was sampled down to a depth of 7.5 m. Sampling was repeated in a control area outside and adjacent to the ARG system. X-ray diffraction patterns clearly show the presence of illite, chlorite, kaolinite, smectite, and sepiolite. Single laths and bundles of laths of palygorskite–sepiolite, a well-formed 6-sided and a pseudohexagonal flake of kaolinite, and smectite particles with smooth, wavy edges are clearly seen in the transmission electron micrograph. The order of clay mineral accumulation at a depth of 7.5 m was as follows: sepiolite > palygorskite > chlorite. The relatively high concentration of sepiolite may indicate its neoformation in the rooting zone of river red gum (Eucalyptus camaldulensis Dehnh.).