Shallow Groundwater Quality Assessment for Irrigation Purposes Based on Irrigation Water Quality Criteria and Its Zoning with GIS in the Guenniche Plain (North Tunisia)

Twenty (20) shallow wells were sampled during the dry season (October 2015) from the Guenniche plain (Northern Tunisia) and examined for their suitability for irrigation. The physicochemical analysis results are used to estimate 10 indexes: the sodium absorption ratio (SAR), percentage of sodium (Na %), residual sodium carbonate (RSC), permeability index (PI), magnesium ratio (MR), residual sodium bicarbonate (SBC), salinity hazard (SH), potential salinity (PS), soluble sodium percentage (SSP), and Kelley’s Ratio (KR). The majority of the criteria (SAR, %Na, RSC, PI, KR, and RSBC) indicate that 100% of the studied water is ‘permissible’ for irrigation. But the rest of criteria show different results. The PS results classify 90% of the samples into the “moderate to satisfactory” category due to high chloride (Cl−) values (average Cl− value 589 mg.l−1) and SH index shows that 65% of groundwater samples are falling in the ‘doubtful’ category. The use of the IDW method for the spatial distribution of the criteria points out that central area and East of Guenniche plain are characterized by the low groundwater quality for irrigation purposes. The improvement of the efficiency of irrigation fertilization in those areas’ practices would improve the water quality of the Guenniche shallow aquifer.