Geospatial Assessment of Turbidity Along the Ganga River

The Ganga River basin is a lifeline to the millions inhabiting the Indian subcontinent. Pollution and deteriorating water quality in this ecosystem have been linked to various anthropogenic activities such as habitation, industrialization, agriculture, etc. The estimation and evaluation of water quality levels are essential for societal and economic development. In recent times, satellite imaging approach is widely used in diverse environmental applications, including water quality monitoring. Turbidity is an indicator of water transparency that is associated with total suspended sediment concentration and other impurities in the water through the process of light attenuation. The present study envisaged surface reflectance values to estimate the water turbidity across the Ganga River system, which is spatially classified into four different river sections. The Modified Normalized Difference Water Index (MNDWI) was used to delineate water pixels from the multispectral satellite datasets, while the turbidity was assessed spatially for different river sections using widely used Turbidity retrieval algorithms. The relative consistency among the selected algorithms was evaluated using collocated in-situ measurements during the period 2013–2016. Analysis of turbidity values showed a steady decrease from upstream to downstream, with turbidity values of >115 NTU and 60–85 NTU in the upper and lower sections, respectively. The results indicated that remote sensing provides a robust alternative for monitoring surface water turbidity.