Assessment of Surface Water Quality Using Entropy-WQI, Fuzzy-TOPSIS Analysis, Irrigation Indices and Spatial Interpolation Approaches in Mahanadi River Basin, Odisha, India

The current study is aimed at the assessment of surface water quality in the Mahanadi River, Odisha and its suitability for agricultural and consumption purposes, utilizing various indices of water quality such as Entropy Water Quality Index, Osmotic Pressure, Potential Salinity, Residual Sodium Carbonate, Sodium Adsorption Ratio and Kelly Index. Multi-criteria decision-making (MCDM) mechanisms namely, fuzzy-TOPSIS modeling and GIS tools were used; additionally, the suitability of river water for industrial uses was evaluated using indices such as Ryznar Stability Index and Puckorius scaling index. From 2019 to 2023, samples from 19 sampling stations were collected and 21 physical and chemical parameters were evaluated and compared with the normative recommendations advised by WHO. The dispersion of surface water quality on land use changes was discovered using GIS approaches. Additionally, using ArcGIS software, the spatial variability of hydrological processes was determined using the IDW interpolation approach. The pH levels of certain sampling points were slightly above the acceptable limit. Tests revealed that the Total coliform (TC) and turbidity levels in the water samples exceeded critical limits, particularly in areas of the urban river basin that were irrigated with wastewater. The calculated values of EWQI lie between 14.6 and 1066. Entropy WQI values designated 2 locations (ST-8, 19) out of 19 sampling locations as poor category and another one testing point (ST-9) as extremely poor category. The study found that 84.21% of the water samples were of excellent quality for drinking, while 15.78% of locations had poor or extremely poor water quality. However, some indices were favorable for the usage of the water for irrigation purposes. Magnesium hazard (MH) readings at two sampling sites were above 50%, indicating that they were inappropriate for irrigation. USSL (United States Salinity Laboratory) diagrams categorized the water samples as C1-S1 (low salinity and low sodium) for almost 18 sites and C4-S3 (very high salinity and high sodium) for only ONE sample, respectively, suggesting river water's irrigation suitability. Further, Piper diagrams revealed that most investigated waters were Ca2+-Mg2+-Cl- water type. In a later stage, from Gibb's diagram, it was found that most samples fall under the rock-water dominance. Based on the above and all other investigation results, it was concluded that water is suitable for irrigation and drinking purposes in all sites, except for three locations. The reason may be due to long-term use of wastewater, anthropogenic activities, over-extraction of surface water and changes in land use patterns. To sum up, it is advantageous to combine physicochemical properties, EWQI, fuzzy-TOPSIS, and GIS tools to evaluate surface water suitability for consumption and agriculture and their regulating variables. The strategy utilized in this work will aid the water management authorities in ensuring the supply of safe water for stakeholders.