Effect of groundwater table decline on groundwater quality in Sirjan watershed

الملخص EN

Sirjan watershed, with an area of about 8,027 square kilometers, is located in Kerman province, which is in the southeastern part of Iran.

In the last few decades, a lack of water resources in this plain and a growing discharge of groundwater led to a significant decline in groundwater tables.

As a result, the annual average groundwater table also dropped significantly–an average of 70 cm / yr from 1984 to 2005.

Furthermore, because the Sirjan watershed is located close to the Kafeh Namak (Salt Groundwater Desert), the water table decline in the Sirjan aquifer led to greater saltwater interface in the Sirjan freshwater aquifer.

This caused a deterioration of groundwater quality in major parts of the watershed.

In this study, water table fluctuation of the Sirjan aquifer is simulated with PMWIN 5.1 software.

The simulation model is calibrated using observed data from 1998 to 2005.

Parameters including hydraulic conductivity, storage coefficient, and recharge content are estimated with the PEST subroutine.

In addition, groundwater quality and factors that may influence the quality of this aquifer were evaluated.

These factors included the effects of saltwater intrusion and Miocene marl sediments in some parts of this aquifer on groundwater quality.

The chemical analysis data related to two time periods between 1984 and 2005 was compared.

The average chemical composition of groundwater samples included Na+, Ca2+, Mg2+, Cl-, HCO3-, and SO42- concentrations and Electrical Conductivity (EC) of groundwater.

The results of this model contain predictions of groundwater table variations for the next eight years.

Finally, three groundwater discharge management scenarios were defined to estimate how much the well discharge should be decreased to stop water table decline in the Sirjan aquifer.

The results show that in order to balance the water budget of this aquifer, groundwater discharge must decrease by 30 percentage points.

The results from the model also indicate that with the current trend of groundwater discharge in this watershed, stored freshwater will be exhausted early, and groundwater quality in major parts of the watershed will fall.