Missed potential and way forward

Hyderabad is one of the fastest-growing urban agglomerations in India with an annual population growth rate of more than 5 per cent. But the city has suffered endlessly from floods.

In one of its worst spells in August 2008, the city received 237 millimetres of rainfall — 28 per cent of annual rainfall — in over 72 hours. It affected more than two lakh people. Property damages in the city alone were estimated to be Rs 50 lakh.

On September 21-22, 2016, the city received 166 mm of rainfall, submerging roads and properties in the low-lying areas.

In the most recent spell, on October 17-18, 2020, the city recorded rainfall in excess of 200 mm overnight, resulting in a flurry of run-off that submerged the entire city. More than 76 people have died; damages have been pegged at Rs 1,000 crore.

It is evident that the annual rainfall has been increasing with time and is likely to result in more instances of urban flooding. While the city grapples with urban floods frequently in a changing climate, the response to prevent urban floods remains toothless: The strategies are limited to provisioning of more drainage channels.

Hyderabad is located on the ridge of the Krishna and Godavari river basins, approximately 150 kilometres away. With the undulating hilly topography of the Deccan region, Hyderabad and its environs were dotted with a number of natural water bodies such as lakes and tanks.

In addition to these, successive rulers built various tanks from the 16th-18th century such as Hussain Sagar, Mir Alam Tank, Afzal Sagar, Jalpalli, Ma-sehaba Tank, Talab Katta, Osmansagar and Himayatsagar.

A number of small tanks were also built by the zamindars during these times. Historically, the city comprised 400 lakes. At least 48 flood absorbing tanks were built as part of a stormwater system in 1912-1929.

These water bodies provided cushions to absorb and store rainwater. Most of them have been converted into housing colonies by reclamation, according to Agarwal, A and Narain, S, 1999 (Dying Wisdom).

The city has grown spatially to 729.9 square kilometre (2014) from 216.7 sq km (1990), with an exponential increase in the built-up area at the expense of water bodies and open spaces in the city.

Currently, only 169 lakes exist in the city. Several water channels that used to carry floodwaters from one lake to the next in a catchment area have also been encroached by private and government agencies.

The existing urban stormwater management in the city is largely based on conventional approaches implemented in developed countries during the 20th century, which aimed to evacuate the run-off from the city as quickly as possible instead of endeavouring to store and reuse it.

This means constructing more and more grey infrastructure constituting road-side drains. Here, the design standard accounts for three-five years return period run-off. The service-level benchmarks (SLBs) focus on only on construction or retrofit of these road side drains for stormwater management.

However, this approach alone is limited in its ability to account for uncertainties in climate projections as well as to manage precipitation events that are more extreme than considered in design standards.

The road-side drainage infrastructure in the city is under multiple authorities: The Greater Hyderabad Municipal Corporation (GHMC), the Public Works Department (PWD) and the Hyderabad Metropolitan Development Authority (HMDA) are the major players.

In addition to these, the natural drains in the city and the extended metropolitan areas are under the Telangana Irrigation and CAD department. Desilting exercises are also carried out by GHMC in some natural drains.

A majority of lakes in the city are under GHMC and HMDA, whereas their catchment areas are under multiple public and private ownerships.

Due to multiplicity of authorities, there are issues of coordination and lack of enforcement, and the stormwater infrastructure is largely unequipped to handle moderate and extreme rainfall events.

Way forward

To address urban issues of the 21st century, we need to look beyond the Victorian engineering solutions and adopt new perspectives.

There is a need to push for alternative stormwater management techniques that can lead to a sustainable groundwater infiltration, protect local water bodies as well as avoid urban flooding in the long run. This amounts to lowering hydrological impact of urbanisation and increasing the carrying capacity of urban areas.

• Protecting local water bodies (lakes, ponds and wetlands) that act as sponge in high-rainfall events, hence reducing the volume of rainwater run-off and lowers the risk of flood and water logging

• Promoting rainfall infiltration into the soil at public places, including open areas in cities through elements of landscape design of vegetated swales and bio-retention systems.

The city has 1,017 parks and playgrounds spanning 281 hectares that provide potential for moderating run-off through principles of retention. They also help in recharging groundwater through infiltration.

These strategies should also address issues of integration of urban drainage with other urban services and urban planning with regular observations and management.

Risk and vulnerability assessment is as an essential part of the stormwater masterplan, which will inform regarding the following:

• Flood-prone areas

• Chronic water-logging locations

• Vulnerable residential areas and potential population that can be impacted due to flood

Moderating floods

Alternative and additional measures (storage / infiltration / delayed surface run-off) remain relatively unused in the city. These techniques help to reduce not only flood events and the creation of stagnant ponds but also the volume of contaminated water discharged into the environment.

Stormwater management plans must contain an inventory of existing and planned public parks, open spaces and water bodies.

This important information about preserving natural features such as water bodies and watershed areas should be supported with a list of evaluated alternatives such as using traditional drainage channels (gray) infrastructure versus more efficient and economic low-impact (green) infrastructure.

As the city expands, areas must be planned and developed on the principles of water-sensitive design and planning, that is, parks and open spaces should be planned and designed for infiltration.

As per the planning norms, parks of area up to 2,000 sq m are to be provided for 500-2,500 households. Neighborhood parks of area between 2,000 and 10,000 sq km and community parks of area between 2 and 20 hectares are to be planned and developed. These open spaces provide immense potential for flood mitigation for future development areas.

Collaboration between stakeholders

Nothing is possible without collaboration to develop the required linkages between different expertise. The specialists and stakeholders need to harmonise stormwater management related activities.

The city needs to put stormwater management in line with urban planning — as part of an integrated and interactive process between architect / urban designer, planner, landscape architect; ecologist, hydrologist, academician; engineer, contractor; local authorities; non-profits, resident welfare associations and local residents.

(Courtesy: Down To Earth)