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Managing Urban Flooding: Challenges and Solutions
Context:
Recently, the India Meteorological Department (IMD) warned us of very heavy rain in Mumbai and Thane.
Overview of Urban Flooding and Impact:
- Urban flooding refers to the rapid rise of floodwaters in urban areas due to limited infiltration and heavy rainfall events, which can lead to human casualties, property damage, and disruptions to transportation and businesses.
- According to the NDMA, Urban flooding is distinct from rural flooding due to developed catchments, increasing flood peaks by 1.8 to 8 times and flood volumes by up to 6 times.
- Flooding in urban areas occurs rapidly due to quicker flow times, often within minutes. Urban areas are densely populated, and flooding can lead to loss of life, suffering, and exposure to infections.
- Urban centres are critical for economic activities and infrastructure, making flood management crucial to prevent widespread disruptions and potential global impacts.
- Urban flooding can lead to temporary relocations, damage to amenities, deteriorated water quality, and risk of epidemics.
- In India, significant flood incidents were recorded in Hyderabad in 2020 and 2021, Chennai in November 2021, Bengaluru and Ahmedabad in 2022, in parts of Delhi in July 2023, and Nagpur in September 2023 (forcing many residents to abandon the city and flee).
Causes of Urban Flooding:
- Heavy Monsoon Rainfall: Intense rainfall events.
- Storm Surges: High sea levels impacting coastal areas.
- Dam Water Releases: Sudden discharge of water from dams.
- Urban Heat Island Effects: Increased temperatures in cities.
- Climate Change: Global shifts affecting weather patterns.
- Drainage Systems: Often designed for lower rainfall intensities, and overwhelmed by higher intensities due to poor maintenance and encroachments.
- Encroachments: Reduce capacity of natural drains and floodplains.
Central Government Initiatives:
- National Guidelines for Urban Flooding: Issued by the NDMA to guide ministries, states, and local bodies in creating disaster management plans.
- The Ministry of Housing and Urban Affairs (MoHUA) has issued Urban and Regional Development Plans Formulation and Implementation (URDPFI) Guidelines, 2014 by integrating NDMA guidelines.
- Manual on Storm Water Drainage Systems, 2019: Provides guidance on the sustainable design and management of storm water drainage systems and flood response.
- AMRUT 2.0 Scheme: Focuses on rejuvenating water bodies and wells, including rainwater harvesting through storm water drains.
- Flood hazard assessment and mapping is used to identify areas at risk of flooding, and consequently to improve flood risk management and disaster preparedness
- Early warning system for flooding.
Urban Flood Management:
Managed by State Governments and Urban Local Bodies/Development Authorities, responsible for drainage and sewerage systems.
Fifteenth Finance Commission Allocation:
- Total: ₹2,500 Crore from the National Disaster Mitigation Fund (NDMF).
- Metro Cities: ₹500 Crore each for Mumbai, Chennai, and Kolkata.
- Other Cities: ₹250 Crore each for Bengaluru, Hyderabad, Ahmedabad, and Pune.
Chennai Basin Project: ₹561.29 Crore approved, with ₹500 Crore from the Central Government.
Way Forward:
- Climate Action Plans (CAPs):Develop CAPs tailored to local needs.
- Make CAPs mandatory and integrate them into development policies.
- Innovative Mitigation Methods:
- Use rooftops for infiltration to offset ground permeability loss.
- Install Rainwater Harvesting Tanks to significantly reduce floodwater.
- Water Detention Ponds: Create detention ponds in open areas, inspired by Hong Kong’s Tai Hang Stormwater Storage Tank.
- Permeable Pavements: Implement to decrease runoff.
- Policy and Planning: Formulate a national policy to manage city over-densification and support smaller cities to alleviate migration pressures.
- Promote sustainable growth and educate citizens on disaster risk reduction.
Overview of China’s Sponge City Program:
The 15-minute neighbourhood:
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