The hydrogeology of the Tabriz area, Iran

The present project area lies in East Azarbijan in the north-west part of Iran, and comprises the Tabriz Plain (about 3000 km2) and part of the surrounding mountain area (about 45(X) km2). Climatically, the Tabriz area has hot and dry summers and cold winters with average precipitation ranging from 2(X)mm in the lowland to 5(X)mm in the higher mountain area. Three main aquifers supply drinking, domestic, industrial and most part of the agricultural water to Tabriz City and its surrounding urban and rural areas. They are (1) the unconfined Sahand Plio-Pleistocene volcanic and volcano-sedimentary Alluvial Tuff aquifer which lies to the south and south-west of Tabriz, (2) the unconfmed alluvial fans that lie in the north and southern parts of the Plain, and(3) the multi-layered aquifer system which" lies in the central part of the Plain. The average thickness of these aquifers are about 2(X)m, 50m and 60m respectively. Long-term declines of ground water level are indicated in some parts of the alluvial fans and reverse flow of ground water, in the heavily pumping area in the south-west of the Plain, has produced saline water intrusion into the fresh water aquifer. Constant-rate and step-drawdown pumping test data available from different parts of the area, have been analysed by analytical as well as numerical methods to determine the aquifer properties and well characteristics. The resultant values of transmissivity for the Plain and alluvial tuff aquifers range from 500 mVd to 35(X) mVd, and 240 mVd to 1000 mVd, respectively. Due to the lack of observation well data, direct values of storage coefficient could not be determined for the Plain aquifer. However, the values deduced from the numerical method for the confined aquifer of this area ranges between 2.2x10-3 and 2.0x10-5. Values for the alluvial tuff aquifer range from 2.7x10-1 to 1.1x10-1. The step-drawdown test data have been analysed by a number of methods. The well loss factor (C) and aquifer loss factor (B) range from 1.0x10-7 to 1.1x10-8 d2m-5 and 4.66x10-3 to 4.14x10-4 dm-2, respectively. With respect to geological conditions and ground water quality, the area was divided into three hydrochemical zones i.e., alluvial tuff, northern part of the Plain, and southern and central parts of the Plain. The values of TDS in the ground water of these zones range from 150 to 5(X) mg/1, 2(X) to 12(X) mg/1, and 1000 to 5(XX) mg/1, respectively. Bicarbonate type water dominates the alluvial tuff aquifer and higher elevation parts of the northern parts of the Plain. The southern and central parts of the Plain represents a chloride type ground water in some places especially around the River Aji Chay and the area between Tabriz and Soufian. The alluvial tuff water is rich in Ca and Na whereas, the northern part of the Plain is rich in Ca and Mg which reflect the differences in water bearing-layers in the area. The total amount of annual recharge to ground water is estimated to be about 782x1