Spatial and sensitivity analysis of integrated groundwater quality index towards irrigational suitability investigation

Abstract

183 groundwater samples were collected from Birbhum district (a semi-arid region) of West Bengal, India to assess their irrigational suitability. Cations were found in the order of Ca2⁺>Mg2⁺>Na⁺>K⁺ whereas, anions were HCO3‾>Cl‾>SO42−. The average values of trace metals were recorded in the order as Total Fe>Zn2+>Cu2+>Ni2+>Pb2+>Co2+>Cd2+. Water quality for irrigation purpose was assessed through a newly developed Integrated Irrigation Water Quality index (IIWQI) and other existing indices such as sodium adsorption ratio (SAR), residual sodium carbonate (RSC), sodium percentage (Na%), salinity and Wilcox diagram, magnesium hazard (MH), permeability index (PI) and Kelly index (KI), which indicated that groundwater were suitable for irrigation purpose. The sensitivity and uncertainty analysis by Monte Carlo Simulation indicated that Cd2+, TDS, Cl‾ and HCO3‾ were the most influential parameter, which controlled the water chemistry with 83.99% probability of water quality certainty in the range of 0.4–0.6. The GIS distribution maps with Empirical Bayesian Kriging (EBK) modelling through predicted vs measured and semivariograms plots, described the accuracy and robustness of various water quality models. Major hydrochemical facies were normal earth alkaline of Ca2⁺-Mg2⁺-HCO3‾ type and Ca2⁺-Mg2⁺-SO42−-Cl‾ type. Groundwater chemistry of the study area was mainly influenced by the local geological setting and rock weathering. Reverse ion exchange, silicate weathering and rock weathering such as dissolution of aragonite, calcite, dolomite, fluorite, halite governed the hydrochemistry. The study demonstrated the application potential of IIWQI and EBK in groundwater quality studies with potential advantages. The outcome of the study will provide a new insight for effective management of groundwater for irrigation purposes.