Urban Flooding (Disaster Management)

• Encroachment
  of Flood Plains, Mangroves, Wetlands, Lakes, etc.: Rapid urbanization has
  led to the encroachment and destruction of natural water bodies that act
  as natural buffers against flooding. For example,
  • Bengaluru: There were 260 lakes in 1960 and 10 now
  • Mumbai: Mangroves and salt pans have been destroyed for constructing high-end residential buildings 
  • Chennai: Encroachment of wetlands and flood plains 
• Unprecedented Rainfall: Indian cities experience heavy rainfall during the south-west monsoons. The average monthly rainfall in Mumbai in July is 868 mm. Such intense rainfall events overwhelm the drainage systems and cause urban flooding.
• Cyclones and Hurricanes: India’s extensive coastline exposes it to tropical cyclones. The development of coastal cities and towns makes them vulnerable to inland flooding and storm surges caused by cyclones.
•  Unpreparedness in Urban Planning: Many cities lack adequate urban planning and infrastructure to handle urban floods. Unlike cities like Tokyo, which have invested billions in building water discharge tunnels and advanced drainage systems, Indian cities often lack such preparedness.
• Concretization of Cities: The extensive use of concrete and asphalt in urban areas reduces land permeability. It prevents water from seeping underground, increasing surface runoff and exacerbating the risk of urban flooding.
• Urban Heat Island Effect: The phenomenon of urban heat islands, where cities experience higher temperatures than the surrounding countryside, can influence rainfall patterns. The hot air over cities can cause rain-bearing clouds to be pushed up, resulting in highly localized and intense rainfall events.
• Global Warming: Climate change has led to unexpected and extreme changes in rainfall patterns. For instance, Chennai experienced unusually high rainfall in November 2015, with 1200 mm compared to the average of around 400 mm. 

1. Global Examples

1.1 Kuala Lumpur

• Kuala Lumpur, Malaysia’s capital city, has faced significant challenges with urban flooding due to its geographical location and heavy rainfall.
• To address this issue, the city has implemented an innovative solution by constructing extensive water discharge tunnels. Tunnels divert excess floodwater away from the city’s densely populated areas. By creating an alternative pathway for water to flow, these tunnels alleviate the burden on the city’s drainage systems and prevent overwhelming floods.

1.2 Tokyo

• Tokyo constructed a stormwater management system that includes the construction of reservoirs, underground storage facilities, and permeable surfaces to help capture excess rainwater and prevent it from overwhelming the drainage system.
• Tokyo has prioritized the incorporation of green infrastructure, which can absorb rainwater and reduce runoff.
• Installed Early Warning Systems

1.3 Buenos Aires

• The city is flood-prone, but it has installed sensors in more than 30,000 stormwater drains to issue flood warnings in advance.

2. Indian Examples

2.1 Davangere (Karnataka)

Davangere faced recurring urban flooding due to heavy rainfall and inadequate drainage systems. To address this issue, the following was done.

• Improved the city’s stormwater drainage infrastructure 
• Desilted water channels
• Created storage ponds and reservoirs to hold excess water during heavy rains temporarily 

2.2 Agartala (Tripura)

Agartala experienced significant urban flooding due to its geographical location and heavy rainfall patterns. To mitigate the impact of flooding, the city authorities adopted various measures. 

• Construction of flood protection embankments and bunds along vulnerable areas
• Development of rainwater harvesting structures, such as ponds and recharge pits, to capture and store rainwater, thereby reducing the burden on the drainage systems. 
• Improved its sewage and stormwater drainage networks 

1. Standard Operating Procedures (SOP) for mitigating Urban Flooding by the Central Government under the Atal Mission for Rejuvenation and Urban Transformation (AMRUT). It lays down a predefined set of directives or responsibilities for public agencies in a city/town in 3 phases: 

1.  Pre-Monsoon Phase: Preparedness and Planning for Disaster Reduction.  
2. During Monsoon Phase: Early Warning, Effective Response and Management, and Relief planning and execution
3. Post-Monsoon Phase: Restoration and Rehabilitation.

2. Sponge Cities Plan by Urban Local Bodies and State Governments to make cities more permeable. Sponge cities involve the use of porous materials and technologies to improve the city’s capacity to absorb rainwater. E.g. use of permeable material for roads and pavement, contiguous open green spaces, green roofs, etc.

3. National Guidelines on Management on Urban Flooding by the National Disaster Management Authority (NDMA)