Urban Flooding

About Urban Flooding

Urban flooding has become increasingly frequent in India’s major cities (Chennai floods, most recent in Hyderabad), with an increasing impact on life, property and increased incidence of tropical diseases.

Natural Factors Contributing to Urban Flooding in India:

• Monsoon Rains:
  • Example: The Indian subcontinent experiences heavy monsoon rains from June to September. Cities like Mumbai, Chennai, and Kolkata frequently face intense rainfall during this period, leading to waterlogging and urban flooding.
• Topography:
  • Example: Bengaluru’s natural topography, with its undulating terrain, can lead to water accumulation in low-lying areas. This becomes problematic when combined with urban development that disrupts natural drainage patterns.
• Cyclones and Storm Surges:
  • Example: Coastal cities such as Chennai, Visakhapatnam, and Mumbai are susceptible to cyclones and storm surges. The 2017 Cyclone Ockhi caused significant flooding and damage in coastal areas of Tamil Nadu and Kerala.
• Soil Characteristics:
  • Example: Certain soil types, such as clayey soils found in parts of Chennai, have low permeability, leading to poor drainage and increased surface runoff during heavy rains.
• Sea Level Rise:
  • Example: Coastal cities like Mumbai and Chennai are vulnerable to sea level rise, which can exacerbate flooding, particularly during high tides and storm surges. The 2019 floods in Mumbai were worsened by high tide conditions.
• Climate Change:
  • Example: The increasing frequency and intensity of extreme weather events due to climate change are causing more severe and unpredictable rainfall patterns. For instance, the unprecedented rainfall in Kerala in 2018 led to widespread flooding.
• Hills and Slopes:
  • Example: Shimla and other hill cities experience rapid runoff due to their steep slopes, leading to flash floods during heavy rains. The terrain accelerates water flow, increasing the risk of flooding in lower-lying urban areas.
• Seasonal Variability:
  • Example: Cities like Lucknow experience seasonal variability in rainfall, with some years receiving exceptionally high rainfall. This variability can overwhelm urban drainage systems not designed for such fluctuations.

Anthropogenic factors

• Rapid Urbanization without Adequate Planning:
  • Example: The city of Gurgaon, near Delhi, has seen rapid urban development without corresponding improvements in infrastructure. The lack of adequate drainage systems has led to frequent waterlogging during monsoon seasons.
• Encroachment on Natural Water Bodies:
  • Example: In Chennai, extensive encroachment on natural water bodies and wetlands has significantly reduced the city’s capacity to absorb and drain rainwater. The 2015 floods were exacerbated by the loss of these natural buffers.
• Outdated Drainage Infrastructure:
  • Example: Mumbai’s drainage system, parts of which date back to the British colonial era, is not equipped to handle the high-intensity rainfall the city experiences. The 2005 floods highlighted the inadequacies of the city’s drainage system.
• Poor Solid Waste Management:
  • Example: In Kolkata, improper disposal of solid waste often clogs drainage channels, leading to severe waterlogging during heavy rains. The accumulated waste obstructs water flow, causing flooding even during moderate rainfall.
• High Population Density:
  • Example: Delhi’s high population density puts immense pressure on existing drainage infrastructure. During the 2020 monsoon, several areas of the city experienced severe flooding due to the overburdened drainage system.
• Illegal Construction:
  • Example: In Hyderabad, illegal constructions along the Musi River and other watercourses have obstructed natural water flow paths, leading to increased flooding during the monsoon season.
• Lack of Urban Green Spaces:
  • Example: Bengaluru has lost a significant number of its lakes and green spaces to urban development. The reduced capacity for water absorption has led to frequent flooding in several parts of the city.
• Water Mismanagement:
  • Example: In Surat, the release of water from the Ukai Dam without adequate warning during heavy rains in 2006 led to severe flooding. Poor water management practices and coordination issues often exacerbate flooding.
• Unplanned Urban Expansion:
  • Example: Jaipur has expanded rapidly without proper urban planning, leading to the development of residential areas in low-lying regions prone to flooding. The lack of planned drainage networks has made these areas vulnerable to flooding during heavy rains.

 Strategies to Curb Urban Flooding:

• Green Infrastructure:
  • Green Roofs: Installing vegetation on rooftops can absorb rainwater and reduce runoff.
  • Permeable Pavements: Using materials that allow water to infiltrate the ground can reduce surface runoff.
  • Rain Gardens: Small, vegetated areas designed to absorb and filter rainwater.
• Stormwater Management Systems:
  • Retention Basins: Constructing basins to hold excess rainwater and release it slowly.
  • Detention Ponds: Similar to retention basins but usually dry until a storm event occurs.
  • Bioswales: Landscaped channels designed to concentrate and convey stormwater runoff while removing debris and pollution.
• Upgrading Drainage Infrastructure:
  • Enlarging and Improving Drainage Systems: Ensuring that drainage systems are capable of handling increased volumes of water.
  • Regular Maintenance: Keeping drainage systems clear of debris and in good repair.
• Urban Planning and Zoning:
  • Floodplain Management: Restricting development in areas prone to flooding.
  • Elevated Structures: Building homes and infrastructure above anticipated flood levels.
• Smart Technology and Data:
  • Flood Monitoring Systems: Using sensors and IoT devices to monitor water levels and provide early warnings.
  • Predictive Modeling: Utilizing data and simulations to predict flooding and plan responses.
• Community Involvement and Education:
  • Public Awareness Campaigns: Educating residents about flood risks and how to reduce their impact.
  • Community-Led Projects: Encouraging local initiatives to implement flood mitigation measures.
• Nature-Based Solutions:
  • Wetland Restoration: Rehabilitating wetlands to act as natural sponges for rainwater.
  • Urban Forests: Increasing tree cover to enhance water absorption and reduce runoff.
• Regulatory Measures:
  • Building Codes: Implementing stringent building codes that require flood-resilient construction.
  • Stormwater Fees: Charging fees based on impervious surface area to fund flood mitigation projects.

Case Studies:

Several cities worldwide have adopted the sponge city approach, with notable examples including:

• Shanghai, China: Implementing green roofs, permeable pavements, and extensive green spaces as part of its sponge city initiative.
• Berlin, Germany: Utilizing green roofs, rain gardens, and retention basins to manage stormwater and improve urban resilience.
• Singapore: Integrating green infrastructure and advanced drainage systems to transform the city into a model of sustainable water management.

As the incidence of extreme weather events due to climate change, there must be more focus on urban flooding. Guidelines laid down by NDMA for urban flooding should be followed by cities