Urban Floods

Urban flooding is the inundation of land or property in a built environment, particularly in more densely populated areas, caused by rainfall overwhelming the capacity of drainage systems, such as storm sewers. Due to rapid, unscientific, unplanned urbanization across the globe, the carrying capacity of urban areas is often breached leading to impending disasters. The cases of floods in Chennai in 2016, Bangalore, Gurgaon in 2017 are instances of urban flooding. Floods and water-logging show that urban planners have paid scant respect to hydrology.

  • Need for Holistic Engagement : Urban floods of this scale cannot be contained by the municipal authorities alone. Floods cannot be managed without concerted and focused investments of energy and resources.
    • The Metropolitan Development Authorities, National Disaster Management Authority, State revenue and irrigation departments along with municipal corporations should be involved in such work together.
    • Such investments can only be done in a mission mode organisation with active participation of civil society organisations at the metropolitan scale.
  • Developing Sponge Cities: The idea of a sponge city is to make cities more permeable so as to hold and use the water which falls upon it.
    • Sponge cities absorb the rain water, which is then naturally filtered by the soil and allowed to reach urban aquifers.
    • This allows for the extraction of water from the ground through urban or peri-urban wells.
    • This water can be treated easily and used for city water supply.
  • Wetland Policy: There is a need to start paying attention to the management of wetlands by involving local communities.
    • Without doubt, terrain alteration needs to be strictly regulated and a ban on any further alteration of terrain needs to be introduced.
    • To improve the city’s capacity to absorb water, new porous materials and technologies must be encouraged or mandated across scales.
    • Examples of these technologies are bioswales and retention systems, permeable material for roads and pavement, drainage systems which allow storm water to trickle into the ground, green roofs and harvesting systems in buildings.
  • Drainage Planning: Watershed management and emergency drainage plan should be clearly enunciated in policy and law.
    • Urban watersheds are micro ecological drainage systems, shaped by contours of terrain.
    • Detailed documentation of these must be held by agencies which are not bound by municipal jurisdictions; instead, there is a need to consider natural boundaries such as watersheds instead of governance boundaries like electoral wards for shaping a drainage plan.
  • Water Sensitive Urban Design: These methods take into consideration the topography, types of surfaces (permeable or impervious), natural drainage and leave very less impact on the environment.
    • Vulnerability analyses and risk assessments should form part and parcel of city master plans.
    • In a changing climate, the drainage infrastructure (especially storm water drainage) has to be built considering the new ‘normals’.
    • Tools such as predictive precipitation modelling can help do that and are also able to link it with the adaptive capacity of urban land use.

These can all be delivered effectively through an urban mission along the lines of the Atal Mission for Rejuvenation and Urban Transformation (AMRUT)National Heritage City Development and Augmentation Yojana (HRIDAY) and Smart Cities Mission. Urban Flood management will not just help control recurring floods but also respond to other fault lines, provide for water security, more green spaces, and will make the city resilient and sustainable