Urban Rivers Under Pressure: Human-Induced Modifications, Pollution, and Prospects for Restoration—A Case Study of the Assi River, Varanasi

Abstract

Small urban rivers are crucial to global freshwater ecosystems, yet they are disproportionately impacted by human-induced modifications. Existing restoration approaches have primarily focused on large river systems. This study aims to provide a comprehensive, high-resolution assessment of the urban stretch of the Assi River (~7 km) in Varanasi, India, to inform restoration strategies as a representative case study of the challenges faced by small rivers. We used high-resolution unmanned aerial vehicle (UAV) imagery to map the river and collected water quality data from seven sampling sites in October 2022. Our findings reveal a severe loss of multidimensional connectivity. Geospatial analysis revealed extensive encroachment, with built-up areas occupying 137,580 m2 along a 100 m length within the 30 m buffer zone, and channel widths constricted to as narrow as 1 m in some sections. Water quality is severely impaired, with dissolved oxygen (DO) levels dropping to a minimum of 0.2 mg/L and faecal coliform levels reaching up to 2.1 × 108 MPN/100 mL. We propose a UAV-based restoration framework that integrates geospatial data with policy recommendations to reconnect the river. However, a limitation of this work is that it is based on single-season sampling and temporal variations; multi-seasonal campaigns will likely improve the framework. The proposed model for urban river management directly addresses SDG 6.3 and 6.6, which target the reduction of water pollution and protecting water-related ecosystems, respectively, and SDG 11.7, which aims to provide access to green spaces. © 2025 by the authors.