Impact of Encroachment of Floodplains of Adyar River on Chennai Floods

Floodplains are the natural pathways that accommodate the excess water overtopping the riverbanks during high flow times. However, they have become a zone that causes enormous damage and losses during a flood event, primarily due to floodplain-oriented uncontrolled and unplanned urbanization and developments altering the natural linkage and layout of these regions. The fertile soil, proximity to abundant surface and groundwater sources, and higher land value make them more appealing for human settlements. However, their frequent flooding nature is often overlooked. Earlier studies reveal that a large part of the world’s floodplains has disappeared due to haphazard developments, industrialization, and urbanization, this being more prominent in developing nations like India. Most floodplains in the country have been devastated, floodplains of the rivers Adyar, Cooum, Kosathalayar, Yamuna, and Periyar being a few to list. This study assesses the impact of encroachment of floodplains of the Adyar River of the Chennai basin, in India, on the flood flow pattern using Landsat images and hydrologic–hydraulic modeling of the 2015 flood event. The study puts forth a concise idea of the possible flood flow pattern that would have developed during the 2015 flood event if the floodplains were as in 1991 or prior years, unaltered by unnecessary human interventions, depicting the impact of encroachments. The study reveals that the area has undergone rapid urbanization and haphazard encroachments along the Adyar River floodplains resulting in a 188% increase in flood peak and a 48-h reduction in the time to peak of flow. Better late than never—proper floodplain management and strict implementation and execution of floodplain development regulations and guidelines can still be a solution for these impacts and thus reduce the havoc situation and losses created by a flood.