A geospatial approach to assess River diversion impacts on floodplains: a case of ulwe River

Abstract

Urban rivers in India face escalating environmental stress due to rapid urbanization, unplanned land use, encroachment, and insufficient stormwater management infrastructure. The Ulwe River basin in Navi Mumbai exemplifies these challenges, with its floodplain undergoing significant transformation from natural wetlands and open water bodies to built-up urban areas. The thesis studies how such land use modifications during the period 2016–2024 have affected surface runoff processes and flood hazard in the Ulwe River floodplain. The site and subject were selected for their strategic position in the Mumbai Metropolitan Region, susceptibility to mega-infrastructure projects (most notably the Navi Mumbai International Airport), and as a representative case of Indian urban floodplain change. The research aims to measure quantitatively surface runoff changes, evaluate the hydrological effects of urban expansion, and provide recommendations to inform sustainable urban planning and flood management. A robust methodology was used, combining high-resolution satellite imagery, fieldbased land use classification, and proven hydrological modeling. Land use mapping, grounded and verified by ground surveys, monitored changes in vegetation, wetlands, water bodies, and impervious surfaces over time. Soils in the area are characterized as sandy clay loam, which permitted the study to concentrate mainly on the influence of land cover change and rainfall variability on surface runoff. Surface runoff calculations were carried out using established hydrological processes, with soil and land use data normalized to ensure comparability between years. The research established growth in impervious surfaces (roads and construction) compared to natural land uses (vegetation and wetlands). This has led to increased surface runoff and reduced infiltration and thus more monsoon flood hazard. Spatial analysis revealed unequivocally a loss of natural flood buffers and consequently more urban floods. The research demonstrates the causality of link between land use change in the urban area and the altered hydrologic response in the floodplain. The research has implications for urban planning and flood risk reduction. The increased surface runoff associated with urbanization implies that we require sustainable land use planning, green infrastructure, and wetland restoration to minimize flood risk. The research also demonstrates how geospatial analysis, and hydrological modeling can be integrated to analyze the effect of urbanization on floodplain processes. In conclusion, this study offers a well-substantiated assessment of the impacts of high-rate urbanization and land cover modification that have led to rising surface runoff and flood vulnerability within the Ulwe River basin. Findings reveal the necessity of preventive planning strategies such as preservation and restoration of the natural floodplain features for establishing resilient and sustainable urban development. The results are intended to guide policymakers and urban planners in their policy and decision-making regarding flood risk management and ecological sustainability in rapidly growing urban river corridors. Keywords: River Diversion, Hydrological Alteration, Flood Risk Assessment, Surface Runoff, Floodplain Dynamics, Geospatial Analysis,