A “sponge city” is an urban initiative that employs nature-based solutions like permeable surfaces, canals, ponds, and wetland restoration to enhance water absorption, drainage, and flood resilience. The goal is to mitigate waterlogging and urban flooding caused by rapid urbanization and impermeable surfaces.
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.
It 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. In built form, this implies contiguous open green spaces, interconnected waterways, and channels and ponds across neighborhoods that can naturally detain and filter water. It implies support for urban ecosystems, bio-diversity and newer cultural and recreational opportunities.
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.
The shallow ends surrounding the water bodies in the cities need to be protected from encroachment. Regardless of ownership of these areas, land use on even this small scale needs to be regulated by development control.
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, we need to consider natural boundaries such as watersheds instead of governance boundaries like electoral wards for shaping a drainage plan.
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. These not only reduce run-off and the load on infrastructure, but also help keep water in the city for later use.
