Mains Practice Questions

Introduction :

India’s rapid urbanisation has frequently ignored natural landforms and drainage systems, with floodplains, wetlands, and river channels being converted into built-up areas.

• Recurrent floods in cities like Chennai and Bengaluru show how neglect of geomorphological and hydrological realities turns heavy rainfall into human-induced disasters, while also accelerating environmental degradation and undermining urban sustainability.

Body:

Ignoring Geomorphology and Hydrology- Fueling Urban Floods & Environmental Degradation:

• Soil Sealing and the "Flash Flood" Effect: In natural landscapes, geomorphology dictates where water infiltrates or flows. Urbanization replaces permeable soil with impervious surfaces like concrete and asphalt.
  • This "seals" the soil, preventing infiltration and forcing water to become immediate surface runoff.
  • Due to this peak flood discharge can increase by 1.8 to 8 times its natural level, and runoff volume can grow by up to 6 times. (NDMA).
• Encroachment on Natural Floodplains: Geomorphologically, floodplains are the "safety valves" of a river. They are flat areas designed to hold excess water during surges. Ignoring this and building on these lands removes the river's capacity to store water.
  • When a river cannot expand sideways into its natural floodplain, the water level rises higher and moves faster, causing "fluvial" (river) flooding in developed areas.
  • For example, in Mumbai, construction on reclaimed land and obstruction of tidal creeks like the Mithi River worsened the 2005 floods, when nearly 944 mm of rain fell in 24 hours.
• Destruction of "Urban Sponges" (Wetlands and Lakes): Hydrology relies on low-lying areas such as wetlands, marshes, and lakes, to act as natural detention basins. When these are filled in for real estate, the city loses its natural storage capacity.
  • Without these "sponges," even moderate rainfall can lead to severe waterlogging as the engineered drainage systems are quickly overwhelmed.
• Disruption of Groundwater Recharge & Subsidence: Ignoring hydrology doesn't just cause too much water on top; it causes problems underneath. By blocking infiltration, cities prevent the recharge of aquifers.
  • As cities pump out groundwater for a growing population but fail to put any back in (due to paved surfaces), the land can actually sink (subsidence), making the city even lower and more prone to flooding.
  • For instance, Joshimath in Uttarakhand has witnessed land subsidence due to excessive groundwater extraction, unplanned construction, and obstruction of natural drainage in a fragile Himalayan geomorphological setting.
• The "Urban Heat Island" and Hydrological Feedback: Geomorphology is not just about height, it’s also about thermal properties. Natural landscapes (forests and wetlands) regulate temperature through evapotranspiration. When these are replaced by concrete, the city traps heat.
  • This "Urban Heat Island" (UHI) effect can actually alter local weather patterns. Hotter air over cities can trigger more intense, localized "convective" rainfall.
  • The city creates its own "micro-monsoons," dumping massive amounts of water on a surface that is already hydrologically "sealed," leading to instant flooding.

Measures to Address Geomorphological and Hydrological Neglect and Urban Vulnerability:

• Protect and Restore Natural Flood Buffers: Protecting and restoring urban wetlands, floodplains, lakes, and mangroves should be a priority, as these ecosystems act as natural sponges during heavy rainfall.
  • Cities should adopt the sponge city concept by integrating permeable surfaces, urban wetlands, and green infrastructure to absorb and regulate rainwater, thereby reducing floods and improving groundwater recharge.
  • Scientific mapping using GIS, legal notification of wetlands and floodplains, and strict anti-encroachment measures can prevent further degradation and help revive the natural flood-regulation capacity of cities.
• Integrate Terrain and Water in Urban Planning: Urban planning must incorporate geomorphological and hydrological realities by adopting watershed-based and terrain-sensitive master plans.
  • Strict enforcement of floodplain zoning, coastal regulation norms, and hill-area construction guidelines is essential to prevent construction in ecologically fragile and flood-prone zones.
• Upgrade Climate-Resilient Drainage Infrastructure: Cities need modern stormwater drainage systems designed for future rainfall extremes rather than outdated historical averages.
  • This requires widening and desilting drains, separating sewage from stormwater networks, and ensuring regular maintenance to avoid blockages and urban inundation.
• Promote Nature-Based Urban Solutions: Nature-based solutions such as permeable pavements, green roofs, urban forests, rain gardens, and compulsory rainwater harvesting should be promoted through building by-laws and fiscal incentives.
  • These measures reduce surface runoff, enhance groundwater recharge, and improve overall urban environmental health.

Conclusion :

Urban floods in India are increasingly the result of ignoring natural geomorphological and hydrological realities rather than rainfall alone. The loss of wetlands, poor drainage, and terrain-blind urban growth have amplified flood risks while degrading urban ecosystems. Aligning urbanisation with nature is essential for building resilient, sustainable, and liveable Indian cities.