Assessing the impact of the Imphal Flood of 2024 on hydrochemical constituents of surface water bodies and shallow groundwater in the Imphal Valley of Northeast India

This study analysed the spatio-temporal changes in hydrochemical constituents of various water bodies before and after the Imphal Flood of 2024. A total of 166 samples were collected, revealing an overall increase in key hydrochemical parameters in surface water post-flood, indicating a considerable impact on water quality. In contrast, groundwater exhibited decreased concentrations, suggesting greater stability against flooding. Surface water pH remained neutral with slight alkalinity, while groundwater pH increased following the floods, highlighting potential implications for groundwater quality. These changes suggest that floodwaters may have influenced the hydrochemistry of these waters, potentially affecting its appropriateness for various uses. The results further showed that rock-water interaction is the chief factor influencing hydrochemistry, with silicate weathering identified as the primary source of major ions. Cation exchange reactions indicated an imbalance in hydrochemical composition, emphasizing the influence of anthropogenic actions such as agricultural runoff on water quality. Multivariate statistical analysis indicated that contaminant elements in surface water primarily originated from non-point anthropogenic sources, including agricultural runoff with agrochemicals and poor sanitation due to flooding. Conversely, in groundwater, geogenic factors like mineral-rock weathering and ionic-exchange processes have a more significant effect on water chemistry than anthropogenic impacts. Assessment of human activity impact further suggested that the flood may have altered the hydrochemical behaviours of both surface and groundwater, potentially diluting contamination from previous sewage and agricultural sources. Overall, the study underscores the flood’s significant impact on hydrochemical constituents and emphasises the need for authorities to implement measures such as flood susceptibility zonation, public awareness on flood mitigation, land-use planning, and structural interventions to improve water quality in the affected areas.