Environmental Assessment of Channel Dredging Impact on Water Quality: A Case Study of the Ghaghara–Saryu River, Uttar Pradesh, India

Abstract

Channel dredging is an essential river management practice for controlling floods, maintaining navigational depth, and managing sediment dynamics in riverine systems. This study presents a comprehensive environmental assessment of the water quality impacts of channel dredging operations conducted on: (1) the right bank of the Ghaghara River at Siroli Goong village and neighbouring villages in Barabanki District, and (2) the left bank of the Saryu River at Bahadur village and surrounding villages in Gonda District, Uttar Pradesh, India. Water samples were collected during pre-monsoon (May 2025) and post-monsoon (November 2025) seasons across upstream, mid-channel (transition zone and dredger location), and downstream sampling points. Key physicochemical parameters including water depth, Secchi disc depth, pH, Dissolved Oxygen (DO), Electrical Conductivity (EC), turbidity, Total Dissolved Solids (TDS), and Total Suspended Solids (TSS) were measured in accordance with APHA (2017) and BIS IS 3025 standards. Heavy metal analysis using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Particle Size Distribution (PSD) analysis using a Nanoparticle Size Analyser were also conducted. Results indicate that dredging significantly elevated turbidity and TSS at and immediately downstream of the dredging site in both river systems during the pre-monsoon season, with maximum turbidity reaching 445 NTU (Ghaghara) and 405 NTU (Saryu) at the dredger locations. All detected heavy metals (Barium, Aluminium, Zinc) remained within WHO and BIS (IS 10500:2012) permissible limits, suggesting no significant heavy metal contamination risk from the dredging activities. Post-monsoon sampling revealed improved water quality attributed to increased discharge and dilution effects. Overall, the dredging operations successfully cleared trapped waste, mitigated flood risks to protect riparian communities, and optimized channel flow, which actively improved water quality by enhancing dissolved oxygen (DO) levels, accelerating the reduction of BOD and COD, and preventing long-term chemical degradation thereby advancing vital social welfare, securing community safety, and ensuring a healthier, more sustainable environment for aquatic life in both river systems.