GEOLOGICAL CHARACTERISTICS OF TEHRAN AQUIFER

Resumo

The alluvial deposits of Tehran is composed of up to 1100 m and is divided into five
parts: The first part (~500 m) has been denominated as first member of Hezardareh Formation and
has been formed of hard conglomerate of Upper Pliocene age. This part has many few porosity, high
erodibility of pebbles and strongly cementation.
The second part (second member of Hezardareh Formation has been composed of ~500 m of
incoherent conglomerate and conglomeratic sandstone deposits of Lower Pleistocene age. This
member has highly porosity respect to first member and less grade of erodibility.
The third horizon (Kahrizak Formation) with 10 to 60 m of thickness contains pebble, gravel
and sand. It is Middle Pleistocene in age.
The fourth stage (Tehran alluvium) with 50 m of thickness has been formed by stratified
gravels of Upper Pleistocene age. In general this Formation is composed of heterogeneous grains
and because of having frail cement between pebbles it is permeable and with relatively high
mechanical resistance. Tehran alluvium has been the better depository of underground water in the
alluvial fan of Tehran region.
The fifth part (Holocene stage) with 1-5 m of thickness contains coating pebbles, gravel and
fine sediments. It is composed of separated and highly permeable deposits, which its mechanical
resistance differs in different part of the region.
The thickness of alluvial aquifer is estimated about 300-350 m, which composed of second
member of Hezardareh and younger Formation.
Much of the groundwater essential to agriculture and human existence emanetes from aquifers
in Quaternary sediments of Tehran plain.
According to our surveys and data, annually water consumption of Tehran city is about 700
million meter cubic which 20.8% of it discharges from Quaternary deposited sediments.