Flood Mitigation through Sectoral Dredging and Geotube-Assisted Flow Diversion: Hydrodynamic Assessment of the Garra River, Uttar Pradesh, India

Abstract

This study assesses the hydraulic and morphological outcomes of a sectoral dredging and flow diversion project carried out on the Garra River near Sanjalpur Village, Hardoi district, Uttar Pradesh, India. The project covered a 2.35 km reach situated roughly 6 km upstream of the Garra-Ganga confluence and aimed to redirect active river flow away from inhabited settlements by guiding the river back toward its 1960s course. The main engineering works included a newly cut 45 m wide channel, a three-layer geotube structure placed as an inline flow deflector, and controlled infilling of the original channel using excavated material. A post-monsoon evaluation after the 2025 monsoon season used multi-temporal Sentinel-2 satellite imagery alongside field hydraulic benchmarks. Results confirmed that the dredged channel carried roughly 75% of total river discharge at a peak recorded water level of 129.15 m. The original channel (The river is causing severe bank erosion near the village) became hydraulically inactive, the dredged channel (new artificial cut off channel) stayed self-scouring and widened naturally to about 100-150 m, and no bank erosion was recorded near settlements. The geotube structure remained intact throughout. Community-level benefits included an end to recurring flood damage and the reclamation of floodplain land for seasonal farming. These results confirm that the sectoral dredging method is a cost effective and process-compatible approach to river training, with lessons that can apply to other migrating alluvial rivers in the Ganga basin.