Remote Sensing and GIS-Based Assessment of Water Quality and Pollution Sources in the Karnaphuli River, Bangladesh

Rapid urban development and increasing anthropogenic pressures have raised significant concerns about the ecological health of major river systems in Bangladesh. This research investigates the water quality dynamics and pollution sources in the Karnaphuli River basin using remote sensing and GIS techniques. Key parameters such as the Normalised Difference Turbidity Index (NDTI), Normalised Difference Chlorophyll Index(NDCI), dissolved Oxygen (DO), and Temperature are assessed between 2014 and2024. The NDTI analysis reveals varying turbidity levels, with the middle section of the river exhibiting the highest turbidity, while NDCI indicates fluctuating chlorophyll-a concentrations (7.198-41.71 µg/L). DO levels show as light decline (7.619–7.898 mg/L), potentially affecting aquatic ecosystems, whereas temperature trends reflect a warming river. Using the Google Earth Engine platform, land-use and land-cover change analysis demonstrates substantial landscape transformation, with built-up areas expanding from 1131.59km² to 1572.58 km² alongside losses of water bodies and vegetation. These changes highlight significant urban and infrastructure expansion, which has serious implications for water quality, as urbanisation typically increases runoff, sedimentation, and pollutant loading. The study identifies multiple pollution sources (e.g., airports, tannery and cement industries) that discharge heavy metals, organic pollutants, and nutrients into the river system. To support sustainable water resource management, the research recommends stronger pollution controls, sustainable land-use practices, enhanced monitoring and research, community engagement, and multi-stakeholder collaboration. This study underscores the urgent need to manage pollution sources and strengthen ecosystem resilience to ensure the long-term sustainability of the Karnaphuli River basin.