Sponge Cities: Solution for Recurring Floods

Context

The highest rainfall in a century received in Hyderabad raised demand for concrete action such as transformation into Sponge cities.

Background

In September 2016, Hyderabad received 16 cm of rain in a single day, that breached a 16-year record, further in September 2017, the city witnessed a 450% increase compared to the average rainfall it receives in the same month, in next year, September 2019, the rainfall was the highest in 100 years, while in October it was in 62% in excess.

Rainfall received in 2020 was the highest for the month of October in a century. Every year, the rains bring something unprecedented with them. The floods in October 2020, occurred essentially because failure in discharging the water in time.

Reasons of Flood in Cities

Antiquated infrastructure and century-old drainage system covered only a small part of the core city. In the last few decades, the cities in India have grown at least four times to its original built-up areas.

Neglect the issues of changes in incremental land use pattern and particularly of those commons which provide us with necessary ecological support like wetlands.

Discharge of sewage and industrial effluents, encroachments by government and private individuals into the water bodies, such as in Hyderabad.

The Frequent use of building material in construction work that are hard, non-porous and impervious to water and thus makes the soil impervious.

In most of the cities the surrounding region of water bodies often called the shallow ends or small wetlands have disappeared because of private encroachment.

Solution: Sponge Cities

Expeditiously launch a mission aims to mitigates flood risk and provides a pathway to water security. The most promising idea across the world at this time appears to be the idea of “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.

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.

Conclusion

The risk is going to increase year after year with changing rainfall patterns and a problem of urban terrain which is incapable of absorbing, holding and discharging water.

Urban floods of this scale cannot be contained by the municipal authorities alone. Nor can they be dealt with by the State government. They cannot be managed without concerted and focused investments of energy and resources.

Such investments can only be done in a mission mode organisation with active participation of civil society organisations at the metropolitan scale.

There is a need to urgently rebuild our cities such that they have the sponginess to absorb and release water without causing so much misery and so much damage to the most vulnerable of our citizens.

Connecting the Article

Question for Prelims

In relation to the concept of sponge cities, consider the following statements:

1. It is a city structure design to absorb and capture rain water.
2. It enables to effectively utilize the rain water.

Which of the statements given above is/are correct ?
(a) 1 only
(b) 2 only
(c) Both 1 and 2
(d) Neither 1 nor 2

Question for Mains

Groundwater over-extraction, waterway degradation, and urban flooding are forcing India's cities to address a vicious cycle. Sprawling urban development and use of impervious material prevent soil from absorbing rainwater that further impede natural processes and worsen flood impacts. How can the concept of sponge cities address this? Explain.