Spatial Variability and Mapping of Shahrekord Groundwater Quality for Use in the Design of Irrigation Systems

 




     Groundwater is the only important water resource for irrigation in the Shahrekord plain.  Due to over-extraction, the water-table is continuously declining.  Drip irrigation has the potential to save water.  The main aim of this research was to investigate the spatial variability and mapping of irrigation water quality of the Shahrekord aquifer.  Ninety-seven agricultural wells were sampled three times during 2010 and samples were analyzed.  Electrical conductivity (EC), total dissolved solids (TDS), total suspended solids (TSS), and pH were measured and the Langelier index (LI), sodium adsorption ratio (SAR), permeability index (PI), residual sodium carbonate (RSC) and sodium percent (Na%) of each sample were calculated from the measured parameters.  The averages of the three samples have been presented here.  The mean EC and TDS were 456 µS/cm and 296 mg/l, respectively, placing the groundwater in, respectively, good and relatively good classes for irrigation. According to Wilcox's diagram, almost all groundwater samples were designated as C₂S₁.  Shahrekord groundwater is suitable for irrigation based on Na%, RSC and PI, too.  Based on mean pH and TSS of, respectively, 7.6 and 70 mg/l, Shahrekord groundwater has medium potential for dripper clogging.  Spatial variability of EC and TDS was best described with a Gaussian model while the other parameters were best described with spherical models. Comparison of the observed and mapped correlations indicated the suitability of the selected variograms and the Kriging method for mapping of parameters.  Maps showed that the values of measured and calculated parameters were higher in the southern part of the aquifer.  Based on the EC map, the groundwater in most parts, except the southern part of the aquifer, was classified as good and very good.   Only in the south of the aquifer did TSS reach 512 mg/l, indicating a medium physical clogging potential in drip irrigation.  The pH and TSS maps indicated a medium potential for clogging of drippers, generally across the aquifer.  At the same time, the Langelier index across the aquifer was generally negative, indicating the suitability for drip irrigation.  The positive LI in some areas of the aquifer may be due to the existence of carbonatic formations and their solubility.