GIS-Integrated Water Quality Indices for Evaluating Irrigation Suitability of Groundwater

This study aimed to assess groundwater quality suitability for irrigation in the Sabi River basin of Rajasthan, India, using geographic information system (GIS). Water quality investigations, before and after the monsoon season of years 2022-23 and 2023-24, involved collection of groundwater samples from tubewells located at 83 sites. Total 13 chemical parameters, i.e., pH, total dissolved solids (TDS), electrical conductivity (EC), sodium, potassium, calcium, magnesium, carbonate, bicarbonate, chloride, sulphate, fluoride, and nitrate were analyzed to understand groundwater chemistry. From irrigation point of view, two parameters (TDS and EC) and nine water quality indices (WQIs), i.e., residual sodium carbonate (RSC), soluble sodium percentage (SSP), sodium adsorption ratio (SAR), Kelly’s ratio (KR), permeability index (PI), magnesium hazards (MH), residual sodium bicarbonate, percent sodium (%Na) and potential salinity (PS), were computed. The WQIs were compared with the standards of irrigation water quality. The results of the WQIs, except MH and PS, revealed that groundwater quality in majority of the basin area was within the acceptable threshold for irrigation. The WQI for the basin ranged from 76 to 147 in pre-monsoon and from 72 to 132 in post-monsoon. This suggested that groundwater quality in whole of the study area was unrestricted during both pre- and post-monsoon seasons and was usable for irrigation. The United States Salinity Laboratory (USSL) diagram indicated acceptability of groundwater at almost all the sites for irrigation during both seasons. Similar finding was revealed from Wilcox diagram, except for groundwater at nine and three sites lying in doubtful to unsuitable class during the pre-monsoon and post-monsoon, respectively. In both the seasons, EC and TDS exhibited positive and highly significant correlations with most of the water quality parameters. The RSC and SSP also demonstrated highly significant and positive correlations with SSP, PI, KR and % Na during both seasons. The study provided valuable information to assist planners and decision makers in better managing groundwater resources and developing water use policies in the area.