Providing Supplementary Water for Bangalore, India: Towards Water Sensitive Urban Design

Vishwanath Srikantaiah, Sarah Martin

www.rainwaterclub.org, zenrainman@gmail.com

Abstract Situated on a ridge and at an elevation of 900 metres above sea level, Bangalore in South India has one of India’s most difficult challenges to meet its water requirements. 810 million litres of water per day is pumped in to the city daily for a population of about 6 million. Another 500 million litres per day will be pumped with a new scheme. There is however a limit to water availability at around 1500 million litres per day. A recent award of a tribunal set up to adjudicate the sharing of river waters between 4 states has capped the water availability to Bangalore city at a very low level. The city is therefore actively supporting alternate source of water including rooftop rainwater harvesting. With an annual average rainfall of around 970 mm, distributed over nearly 60 rainy days the endowment of rain is considerable. Over the cities geographical extant of 1250 square kilometres this translates to nearly 3000 million litres per day. Industries and parks adopt rainwater harvesting in a big way. Building bye laws now make rainwater harvesting mandatory for new buildings. 20 litres of storage or recharge for every square metre of roof area is compulsory for all new constructions. Hydro geological mapping of the surface shallow aquifer has also commenced. Recharging this aquifer with excess rainwater after storage is seen as of great benefit. Private initiative has also started on regenerating and recreating manmade lakes called ‘tanks’ which have dwindled considerably in number. The city is also incorporating eco-san alternatives in the form of composting toilets, small scale decentralised water treatment and reuse systems and large scale decentralised sewage treatment and reuse systems. Open wells, a traditional source of water in the past, are also being mapped with a view to integrate them into the rainwater recharge system as well as in the functionality of water provision. Approximately 10,000 million litres of rainwater is harvested every year. This paper will document several case studies of rainwater harvesting and water sensitive urban design in the Bangalore context as well as the overall approach of the city to manage water in a sustainable way.

Introduction: Bangalore city is the capital of Karnataka state in South India. The population of the city in the 2001 census was 5.10 million. The greater metropolitan area is however is estimated to have a population of nearly 7 million in 2005. As in the case of many other urban areas in India, the piped water to the city comes from a fairly long distance and has to be pumped to a higher altitude. In the city’s case this water is transported over 90 kilometres and a head of 300 metres. The importance of water for the city and its sustainable supply can be realized from the following statement of the draft Master Plan – 2015 a vision statement “ Bangalore City, today, a city in the process of expansion, offers, on the whole, a satisfying range but faces difficulties in keeping with the pace of its own economic and demographic growth. In some domains, the situation may even be considered worrying. This is most true of infrastructure: and critical in the case of water supply. Though the available quantity of water should be sufficient, cuts are getting worse, a large part of the population lives in poverty, and the ground water table is in danger of exhaustion due to massive and accelerated over pumping. We are headed towards a water crisis in due course if an urgent change in direction is not affected. “ The Bangalore Water Supply and Sewerage Board (BWSSB) the institutional water service provider, recognizes a ceiling to the availability of water for the city at 1494 million litres per day (Table 1). It therefore has adopted a strategy of reducing demand, plugging leakages in the system, recycling water and rainwater harvesting to ensure sustainability of water supply in the city. (www.bwssb.org) Water harvesting in the city: The popular definition of water harvesting will be used in this article and that is ‘collection and storage of water for future productive use’. As in most urban areas again, piped water supply to the city was from local lakes and ‘tanks’ (manmade water

bodies). In the year 1896 the first scheme was formulated to bring water from the river Arkavathy through an artificial reservoir called Hessarghatta, about 20 kilometres away from the city. The growing city’s thirst led to the formulation of another project of piped water supply from the reservoir Thippagondanahally on the same river Arkavathy but more downstream of Hessarghatta. TG hally as it was called was 40 kilometres from the city. By 1974 water had to be piped from the river Cauvery from a place called Torekadinahalli. This Cauvery first stage has been supplemented by the Cauvery second, third and fourth stage. The fourth stage has a phase II which is under implementation.

Table 1: Water sources for Bangalore

Year Water source Distance (km) Scheme name

Design capacity

(mld)

Remarks

1896 Hessarghatta reservoir 20 Chamarajsagar 36 River source dry

1933 Thippagondanahalli reservoir 40 T.G. Halli 148 River source dry

Sub-total 184 No longer reliable

1974 Cauvery I stage 95 T.K.Halli 135 1982 Cauvery II stage 95 T.K.Halli 135 1993 Cauvery III stage 95 T.K.Halli 270

2003 Cauvery IV stage Phase I 95 T.K.Halli 270

Sub-total 810 Currently supplied

2007 Cauvery IV stage Phase II 95 T.K.Halli 500 Proposed project

TOTAL 1494

Source: www.bwssb.org The city can thus said to have moved away from the notion of local water harvesting with its piped water supply with its sources far away from the city. The idea of moving back to the system of collecting and storing rainwater is not however new to urban Bangalore. Dr. D.K.Subramanian of the Indian Institute of Science had mooted such an idea in 1984 itself in his seminal article in the publication -Essays on Bangalore – brought out by the Karnataka State Council for Science and Technology in 1985. His article had argued that it would in fact be cheaper and much more economically and environmentally sound to build new ‘tanks’ and harvest rainwater to feed the neighbourhood of the water body with rainwater so collected. Supply side through pumping from distant sources seems to have prevailed and not much action was taken on this idea of localized water supply through rainwater harvesting an idea perhaps far ahead of its times. Interest was subsequently revived in the early 1990’s through individual rooftop rainwater harvesting efforts which gained some publicity. However it is only in the 2000’s that the idea has picked up and been institutionalized in the State water policy, in the building bye laws and in the rhetoric of city planners and managers as well as NGO’s and professionals in the field. Current issues with water in the city: In most parts of the city the supply of piped water is restricted to two to three hours on alternate days. Equity of distribution is an issue with the slums and lower income areas getting much less water per capita than the richer neighbourhoods.

Paradoxically many parts of the city are flooded with as little as 25 mm of rain. Groundwater extraction is very high and water tables are falling in many parts of the city. Ground water contamination especially with nitrates was found in more than 75% of the bore wells sampled. Legal measures: The city corporation called the Bangalore Mahanagara Palike (BMP) incorporated rainwater harvesting into its building byelaws after an extended debate and consultation. Since the 6th of June 2004 it is compulsory for all new buildings to implement rainwater harvesting. Buildings with a plinth area of more than 100 square metres or buildings on plot areas more than 200 square metres have to have rainwater harvesting systems compulsorily. For industrial areas, the Karnataka Industrial Area Development Board (KIADB) has made it mandatory for new industries to have rainwater harvesting. Any construction in the area in the catchment of the Arkavathy River, flowing close to Bangalore and one of the sources of water to the city, has to have rainwater harvesting. Water harvesting at the city scale: Thanks to action by Civil Society groups and a Public Interest Litigation filed in the High Court of the state, directions were issued for the protection of the water bodies in the city. The Lake Development Authority was created by the State government in July 2002 with a mandate for regeneration of all the lakes and tanks in and around Bangalore within the Bangalore Metropolitan Regional Authority jurisdiction. Of the 262 lakes, ponds and marshy wetlands only 81 remain.(www.lakeauthority.com) A comprehensive plan has been taken up to restore 60 of the water bodies in the next 5 years. In the meantime 3 lakes have been restored by the Bangalore Mahanagara Palike and 2 by the Bangalore Development Authority and 12 by the Forest department. These lakes have been designed to receive the storm water from the city and become water harvesting structures. Economic measures and tariff setting: Bangalore has perhaps the best water supply system for a city this large in India. All connections are metered. There is a sliding tariff structure categorized into three broad bands Domestic, Non-domestic and Industrial. Domestic tariff begins at Rs 9/- a kilo-litre and increases in various bands of consumption. Non-domestic begins at Rs 32/- a kilo-litre and also goes up with consumption. Tariff for water consumed by industries in one of the highest in India and is Rs 60 /- a kilo-litre Note : US$ 1= Rs 40 indian. The high tariff for industries has encouraged them to go in for rainwater harvesting. TERI has implemented what it claims as Asia’s largest urban rainwater harvesting project for the B.E.L factory in North Bangalore. The reservoir created has the capacity to collect 176 million litres of rainwater at one time. Other industries with rainwater harvesting facilities include the ITC, Escorts-Mahle-Goetze, Pharmacia,Taegu Tec, John Fowler, Aisin-Nttf ,HAL to name a few. A conceptual framework for water supply to Bangalore is shown in Figure 1.

Figure 1: Conceptual framework for water supply in Bangalore

Conceptual Framework: The conceptual framework sought to work along these lines

a) Determine the total volume and reliability of rainfall in the city and estimate rainwater endowment

b) Determine the forms of harvesting it and storing it. c) Understand the capture and use potential of surface water, shallow ground water and

deep groundwater. d) Determine the flows from various catchments surfaces such as rooftops, paved area,

unpaved area, roads e) Determine the best methods and techniques of harvesting rainwater and optimize

storage systems f) Understand the roles of various stake holders in the process and their contribution

towards rainwater harvesting g) Determine the cost economics of rainwater harvesting h) Determine the Information Education Communication –IEC- campaign, the training

requirements, the legal framework and the economic incentives necessary to make rainwater harvesting possible in the city.

Rainwater incident on the city: The city of Bangalore has a land use area for which a Comprehensive Development Plan exists of 1279 square kilometers. The rainwater incident on the city on various land use are as below in Table 2.

Table 2: Potential for rainwater supply in Bangalore Land use Square kilo-metres Equivalent (MLD) Residential 243.69 565 Commercial 16.44 38 Industrial 38.44 89 Public and semi public 77.88 181 Parks and open spaces 49.09 114 Transportation 116.97 271 Unclassified 22.14 51 Spotted development 32.35 75 Sub-total (dvp area) 597.00 1383 Green belt 682.00 1581 TOTAL 1279.0 2964

Source : STEM, 2000

These figures have been a revelation. For example even considering the metropolitan area of 597 square kilometers the incident rainfall is the equivalent of 1383 million litres per day , more than 1310 million litres per day, the total water that will be pumped in to the city reliably after the completion of all piped water schemes proposed. Adding the additional rainwater falling in the green belt which is of the order of 1581 million litres per day planning for rainwater harvesting would make ecological and economic sense. Expert opinion has projected three scenarios with regard to rainwater harvesting as shown in Table 3.

Table 3: Scenarios for rainwater harvesting

Area Rainwater Incident (MLD) Volume harvestable with collection ratio

(MLD)

20% 10% 5%

Development 1383 277 138 69

Green belt 1581 316 158 79

Total 2964 593 296 148

Rainwater harvesting model for Bangalore: The average normal rainfall distribution for Bangalore is in the Table 4 below:

Table 4: Distribution of rainfall in Bangalore Rainfall (mm) Monthly rainfall (mm) Number of rainy days JAN 2.7 0 FEB 7.2 1 MAR 4.4 0 APR 46.3 3 MAY 119.6 7 JUN 80.8 6 JUL 110.2 8 AUG 137 10 SEP 194.8 9 OCT 180.4 9 NOV 64.4 4 DEC 22.1 2 TOTAL 969.9 60

A simple mathematical model based on typical demand for a family of four, hydrogeological profile in Bangalore, current practices with water storage (the construction of sump tanks to store the intermittent supply received once in two days for one hour) and the practise of usage of groundwater with more than 120,000 bore wells reported in the city. A combination of storage and recharge is seen as the best option at the domestic level. This would bring about 55% for direct consumption and about 45% for recharge of groundwater. Excel calculation sheet are available on www.rainwaterclub.org and shown in Figure 2.

What is the area of your roof ? (m²) 100

What is the size of your tank ? (liters) 2000

What is your daily water consumption ? (liters) 500

Total harvestable water (liters) 87291

Total water stored (liters) 47776 Total water for recharge (liters) 39515

Days serviced in a year 96 Figure 2: Results from Rainwater Club spreadsheet

A typical recharge structure would be a small well of diameter 1 metre and depth 6 metres. Average percolation rate is in the range of 100 litres to 200 litres per hour. Reaching a depth of 6 metres enhances percolation rate and also has the potential of raising the groundwater table for the recharge well to function as a withdrawal well (see Figure 3)

Figure 3: A typical ground section in Bangalore

A typical system of rainwater harvesting combining storage and recharge as shown in Figure 4.

Figure 4: A typical combined storage and recharge system

Designing stormwater drains for recharging: Many industries, institutions and neighbourhoods have minor stormwater drains wich carry only rainwater and catchment pollution is manageable. In such cases recharge wells typically of 1 metre diameter and 6 metres depth is put adjacent to the stormdrain as in the first photograph or within it to ensure that most stormwater is sent into the shallow aquifer. This mitigates urban flooding. Bypass arrangements are always made to avoid accidental pollution entering the recharge well (Figure 5).

Figure 5: construction of combined harvesting systems

Case studies Recharging the shallow aquifer with rooftop rainwater.

The Shah’s house has a 500 m² roof. The rainfall near Dodballapur is around 850 mm. With a coefficient of collection of 0.9. The total harvestable rainwater on the rooftop in an average year of rain is 500x850x0.9 = 382,500 litres. The rainwater comes down from the roof through PVC pipes. It is then filtered in an RCC box filter and then led into two recharge wells (5,500 litres each). The rate of recharge in the wells is low. It takes two days for the water to completely percolate if the wells are full. So sometimes they overflow. However they normally recharge close to 200 thousand litres of water in a year. This has positively impacted the borewell which supplies the Shah’s with water. The Shah’s are considering putting two more recharge wells.

PVCdownpipes Subsurface filter Recharge well

Figure 6: The Shah case study

A manufacturing industry

The factory is located in south Bangalore on a plot of 4 acres. The objective was 0% runoff. Three different kinds of rainwater harvesting systems have been implemented. Four Rain Barrels collect the water from the roof of the factory. This water is directly used for gardening. The stormwater flowing on the paved areas is directed through open drains to a 22,000 litres sump tank, it is also used for gardening. The water from the land is led into the ground through recharge wells. With a depth of 25 feet, they allow the rainwater to recharge the aquifer. The factory is thus storing for gardening more than 12 lakhs litres of rainwater every year and sending to the aquifer about 5 lakhs litres. The design of swales in the open land provides an increase of soil moisture by retaining rainwater and allowing infiltration.

Rain barrels collecting rooftop rainwater Recharge well with filtering material around The pictures below are clear indicators of the enhanced greenery due to increased soil moisture in the swales:

Swale directing the rainwater falling on the land to a recharge well Conclusion: Rainwater harvesting as a supplemental source of water is seeing increasing acceptance in the city. From slum dwellers to industries and at a city scale itself rainwater harvesting is being tried out. Though legal and economic measures are being taken to encourage rainwater harvesting, a lot more needs to be done in terms of systematic training of designers and implementers of rainwater harvesting systems. Greater coordination will also be required at institutional levels to bring the maximum benefit out of the potential. The real revolution is however from the bottom. Effort is needed also to learn from implemented projects as a feedback survey mechanism to set right problems if any and to set an agenda for the future. References:

1. Website of the Bangalore water supply and sewerage board. www.bwssb.org 2. Centre for Symbiosis of Technology, Environment and Management, Bangalore –

STEM- ‘A conceptual frame for rainwater harvesting in Bangalore’ 3. Website of Deccan Herald www.deccanherald.com

4. Lake Development Authority www.lakeauthority.com 5. SWABHIMANA: My Bangalore My rights My responsibilities’ 2004 6. Karnataka State Council for Science and Technology KSCST –Essays on Bangalore,

1985. 7. Bangalore Development Authority- Master Plan -2015 Vision Document, June 2005