Impact assessment of different management strategies implementation on the aquifer using numerical simulation (Case study: Namdan aquifer, Fars province, Iran)

Nowadays, in addition to increase in the population growth, decrease in precipitation and surface flows in arid and semi-arid regions of the world, has caused to increase the extraction of groundwater resources and therefore many problems in this valuable and non-renewable resources. In this regard, assessing, monitoring and prediction of the groundwater resources behavior is significant. In this study, a developed numerical simulation model with finite difference solution using MATLAB was applied to evaluate the groundwater elevation changes in a real case.

The study area is the Namdan aquifer located in the Tashk- Bakhtegan basin, Fars province, Iran. The transient finite difference model was developed to assess the groundwater elevation changes. For setting up the model, the study area zoned manually considering the various factors and finally 50 cells were considered. In addition to the groundwater flow interactions between cells, the interactions between boundary cells and inflows and outflows boundaries took account into the modeling. The recharge parameters were calibrated using try and error method while the hydraulic conductivities were calibrated using an optimization problem with an objective function of minimizing the residual sum of squares of water table prediction and observation (a period of 7 years) using an evolutionary ant colony optimization tool and "R" ^2 "=0.93" obtained. Furthermore, the calibrated model verified for a period of 3 years.

The aquifers condition was assessed in transient condition for a period of 30 years, under 7 various scenarios which have been compiled from climate, utilization, crop pattern and the aquifer restoration plan of Iran indexes. By a decrease of 10% in the precipitation and an increase of 20% in the extractions, the groundwater elevation will drop by 0.9 meter and 6.1 meter, respectively. Changing the crop pattern from wheat to barley which consumes less water, causes 4.4 meters rising in the groundwater elevation. In the removing unlicensed wells scenario, the annual water level rising will be 0.45 meter in average.

The groundwater elevation has been faced with the most changes in the scenario of removing unlicensed wells in all over the study area compared to other scenarios and at the end of simulation period, it would be predicted that the groundwater elevation will increase about 19.6 m. This shows the necessity of paying attention to determining unlicensed wells condition in the aquifer restoration plan more than ever.