Delhi: A heat island deep in water

Delhi is situated along the Yamuna river, which is a source of water as well as drainage. It has 300 Kms long network of canals, 28 major drains (600 kms), 750 minor drains and more than 1000 water bodies, (which have either vanished or have been built upon).

With an average height of about 210 m above mean sea level, the plains area generally slopes from north towards south. The topographical relief is provided by the Delhi Ridge which is the culminating spur of the Mewat branch of the Aravalli. The highest point of the range is near Bhati where it is 318.52 metres (1,045 feet) above sea level. Several seasonal rivulets drain the Ridge such as the Barapullah-Kushak Nala system, the Tekhand rivulet out falling into the Yamuna river and the Palam drain out falling into the Najafgarh Drain.

Based on the topographical characteristics, the National Capital Territory of Delhi has been divided into 6 drainage basins as follows:

Najafgarh Basin (332 Sq.Km.)

Alipur Basin (170 Sq.Km.)

Kanjhawla Basin (216 Sq.Km.)

Shahdara Basin (55 Sq.Km.)

Khushak Nallah - Barapulla Nallah System (95 Sq.Km.)

Mehrauli Basin (160 Sq.Km.)

The natural drainage pattern has worked well for many centuries. However, the balance was and continues to be, disturbed by rapid and indiscriminate urbanisation after Independence when about half a million refugees came to Delhi and its population almost doubled.

New colonies were built upon low-lying watershed areas. A network of concrete drains, dams, barrages, roads and other services were built all over the city, including the Ring Road along the Yamuna river. This considerably reduced the drainage capacity of the river basin, nullahs, rivulets and retention ponds. There have also been significant changes in the soils, vegetation, habitats, hydrology, fauna and flora. With indiscriminate urbanisation, the river today has become a dirty drain which is almost dry during the summer while floods occur during the monsoon due to the release of water upstream.

The water bodies and drainage fall under the jurisdiction of 10 agencies such as the Delhi Jal Board (DJB), Irrigation and flood department, PWD, Delhi Government, DDA, MCD, NDMC, Cantonment Board, etc. This makes it difficult to develop an integrated and coordinated system of flood management. The cleaning and desilting of the drains are usually undertaken as an annual ritual before the monsoon.

The proposals under the Master Plan of Delhi 2021, like adopting the concepts of sustainable urban drainage, bio-drainage, zero runoff drainage and integration of green and blue networks remain neglected. For coordinated development, it is necessary to create a single government platform where all the concerned departments work together.

Sustainable Urban Drainage System (SUDS) is defined as “Collective approaches to manage surface water that take into account the water quantity (flooding), water quality (pollution) and amenity issues”. It focuses on preventive actions and relies predominantly on behavioural changes to be effective.

The basic principles of sustainable urban drainage include the following:

Integration of drainage with the streets, water supply, sewage, solid waste management and land use.

Decentralised planning

Efficient resource management

Appropriate Systems Design

Scalable implementation

Based on these principles, the strategies of sustainable urban drainage include the following:

Surface water moves through swales and filter trenches that remove the pollutants

The peak river discharge is delayed and reduced with the incorporation of retention basins, enabling the storage of water for reuse.

Storage in retention/detention ponds and existing drains mitigates flooding and helps groundwater recharge.

Infiltration of water to ground through infiltration basins and soakaways improves the quality of water and decreases peak discharge, as well as enables groundwater recharge.

Existing water channels and drainage canals in urban areas can be used for continuous on-channel recharge of groundwater, transfer water from these channels to various storage and also store water from the channel with the help of sluice gates. Continuous recharge would take place through deep holes in the channel floor. This requires computer modelling of channel capacities, transfer mechanisms, storage capacities, flood prevention and system operation.

The channel filled with water could constitute an urban waterway. Their cleanliness should be maintained with the use of a root zone system, green bridge, mosquito weed, guppy fish to consume mosquito larvae and aeration.

The channels should be shaped, landscaped and deepened to increase water storing capacity, wherever possible. Their banks can be the green lungs of the city. While serving the function of on-channel groundwater recharge they also modify the micro-climate. The conjunctive use of groundwater along with on-channel recharge could also be possible. The existing dirty drains can be converted into attractive landscape trails and greenways, as has been done in Pune, (Osho Dham Park Nallah) and at other places.

By segregation of rainwater from wastewater disposal, it can be used for recharging of aquifers and irrigation. Zero run-off drainage envisages complete retention of rainwater in the area by creating retention ponds, lakes and swales for flood/rainwater discharge. The present method of draining stormwater through masonry drains entails huge costs and effort, which also endangers the groundwater aquifer. The creation of water bodies in low-lying areas not only solves the drainage problem but also provides a source of recreation, cattle rearing, fishing and improvement for the micro-climate.

The possible retention systems for drainage are given below:

Low area drains (soakaway, in landscaping terms)

Ditches and swales

Permanent retention ponds

Underground collection cistern

Depending on the specific aims to be achieved various retention systems offer different advantages.

To conclude, it is suggested that a unified ‘whole of government platform’ be created for institutional synergy as well as review the Drainage Plan of Delhi, the Delhi Disaster Management Plan, and Unified Building Byelaws. The draft Master Plan of Delhi 2041 and Draft NCR Plan 2041 may be given a fresh look to address the issues of climate and disaster resilience, incorporating new technologies and replacing the 20-year horizon with five-year strategies.

AK Jain is ex-commissioner (Planning), Delhi Development Authority (DDA). The views expressed are personal