Urban Flooding: Status of Sediment Management Strategies in Tropical Regions

Urban flooding is a persistent, recurrent issue in major Indian cities, exacerbated by climate change and rapid, unregulated development. The Chennai floods serve as a stark reminder of the consequences of this failure, with high flood peaks and volumes resulting from the impermeabilization of catchments and the destruction of natural drainage systems.

The core vulnerability stems from the neglect of sediment management. Factors like construction-induced soil erosion, the dumping of solid waste (especially plastics) that clogs drains, the lack of data on local sediment dynamics, and the siltation of dams/reservoirs all contribute to reduced drainage capacity. Furthermore, large-scale encroachment on river floodplains and natural channels (nullahs, lakes) is cited as a major, preventable cause.

The article stresses that generic urban planning, which is often based on models developed for temperate zones, is disastrously inadequate for the Indian Ocean tropics. The region's unique climate (monsoons, cyclones, high sediment flux from major rivers like the Ganga-Brahmaputra), rapid population growth, and intense land-use conflicts necessitate a fundamental shift toward an integrated urban management approach that places sediment management and respect for natural water bodies at its center.

• Relevance in Tropical Urban Regions: Current flood and sediment management models are mostly adapted from temperate contexts; tropical littoral regions like India face different rainfall patterns, erosion rates, and sediment loads.

• Unplanned Urbanization: Encroachment into floodplains and water bodies, combined with rapid urban growth, worsens flood vulnerability in Indian cities.

• Impermeable Surfaces: Expansion of roads and concrete structures reduces infiltration and increases runoff, accelerating urban flooding.

• Drainage System Failures: Existing stormwater drains are undersized, poorly maintained, and often blocked by waste and sediments.

• Sediment Erosion and Reservoir Siltation: Land-use changes (deforestation, mining, road building) increase sediment inflows, while dams/reservoirs lose storage due to siltation, aggravating floods.

• Tropical Rainfall Intensity: Monsoons and cyclones bring highly concentrated, extreme rainfall events that conventional urban planning often fails to handle.