Evaluating the Performance of Drainage System in Dropping Water Table Elevation in Shiraz Plain

Shiraz plain is facing elevated groundwater level problem in its south and south-eastern regions due to increasing population, conversion of farmlands and gardens into residential areas, and destruction of old Qanats that used to drain the plain. To overcome this problem, construction of three drainage aqueducts in the plain started since 2003. So far, more than half of one main aqueduct, with a length of ~15 km, has been constructed at eastern Shiraz. In this study, performance of the drainage system in dropping groundwater level in the plain has been evaluated under different scenarios. First, the hydraulic behavior of Shiraz plain aquifer was modeled using PMWIN. Besides the main aqueducts, measured precipitation and evaporation, recharge and discharge from the aquifer by remaining old aqueducts, wells, and Khoshk and Chenar-Rahdar rivers, and returned wastewater were all considered in the model. After model calibration and verification, the required parameters were determined and groundwater level in the plain was predicted for different scenarios at the end of aqueduct construction.Results reflect a good performance for aqueducts in all scenarios as evidenced by large volumes of drained water in comparison to other inflow and outflows of water in the aquifer. As expected, the lowest inflow, outflow, and drained water were observed in the plain during the drought (3rd scenario), and the highest flows during the wet years (4th scenario). Results indicate that in order for groundwater level to drop to the expected extent, lateral aqueducts should also be constructed otherwise the water drained by aqueducts will be less than half of the expected value.