Rainwater Harvesting for the Bangalore METRO

Biome Environmental Solutions Private Limited

Objective

● To harvest all rain falling on the viaduct

● To prevent flooding at the base of the piers

● To ensure that the landscape can be maintained with rainwater alone

Overview

Name Area Remarks

Viaduct 35 kms in length and 10 metres in width

Effective catchment above ground level

Landscaped Area

30 kms in length and 2.5m in width below the via-duct

Only where there is a median, excluding junctions etc

RWH: Optimal Design

● Cost● Capital● Maintenance

● Safety – RWH Structures in public places. No accidents should happen

● Nuanced design – based on local hydrogeology (rocky areas, high water table areas, filled up areas like Yeshwanthpur). Each span to be considered for site specific details

● Ease of maintenance

● Theft/Miscreant proof

● Ensure that pile foundations are not affected

MONTH DAYS QUANTITY (mm)

JAN 0.2 2.70

FEB 0.5 7.20

MAR 0.4 4.40

APR 3.0 46.30

MAY 7.0 119.60

JUN 6.4 80.80

JUL 8.3 110.20

AUG 10.0 137.00

SEP 9.3 194.80

OCT 9.0 180.40

NOV 4.0 64.50

DEC 1.7 22.10

TOTAL 59.8 970.00

Rainfall pattern in Bangalore : Westerly Rain30 years data

RWH Potential

Annually: 300 Million litres

Catchment description Area(sqm)

Annual Run-off 970mm (KL)

Run off for 30 mm rain in KL (average rain)

Run off for 60 mm rain in KL (heavy rain)

Total proposed length of METRO above ground level(35km length * 10m width)

350000 305550 9450 18900

One span (Distance between 2 piers) (28m length * 10m width)

280 244 8 15

Two spans (Distance between 3 piers)(56m length * 10m width)

560 489 15 30

Bangalore Daily Water Requirement : 1500MLPD

Landscaping details

Important Notes:● Landscaped Area water requirement: Xeriscape: Bougainvillea 1 liter to 4 liter per sqm (www.hmda.gov.in/)

● No of Rainy days when watering of plants will not be required: 40 days - 60 days (despite landscaping being below viaduct)

Estimated Water Requirements

Annually: 90 Million litres

Landscaped Area Description

Area(sqm)

Daily Water Requirement (litres) @ 4l/sqm

Annual Water Requirement (KL) 300 days

Median below Total proposed length of METRO (30km length * 2.5m width)

75,000 3,00,000 90,000

Median below One span (Distance between 2 piers) (28m length * 2.5m width)

70 280 84

Median below Two spans (Distance between 3 piers)(56m length * 2.5m width)

140 560 168

Overall RWH recommendations

● Create a minimum of 15KL effective storage-cum-recharge volume between every 2 spans

● In Rocky Areas create additional storage capacity and do not do ground water recharge

● In Weathered Rock Areas (like MG Road) do a combination of storage and recharge

● Make it a live space – with greenery/art. Not only grey concrete

Storage – Option 1

● Conventional brick masonry sump – water is drawn with bucket

Pros– Immovable asset

Cons– Safety– Not visible

Storage – Option 2

● HDPE/Concrete tank on platform – water flow through gravity

Pros

– Advertising space above ground

– RWH is visually effective

– Water can flow by gravity. Combined with drip irrigation

– Low operations cost for landscaping

– Can be made to order

● Cons

– Theft

– Water will be held in

downpipe even after a

rainfall event

● Design Criteria

– Valve for cleaning/draining of pipes

– Prevent theft (low level discharge tap)

Pre Cast Concrete Tanks

Storage – Option 2

Recharge

● 1.2m diameter and 4m to 6m deep well

(4500 litres to 7000 litres capacity)

● Wells to have an additional grille – for safety

● Annually each well can put 270KL to 420KL of water into the ground

The pit has reach the silt layer

Pit and concrete rings

Placing of the rings

The making of a recharge well

Current Implementation – for every 2 spans

● 2 storage tanks of combined 5.88KL capacity

(1.4mx1.4mx1.5m)

● 1 recharge well (6.1m deep, 1.2m diameter) of 6.9KL

static storage (effective capacity will depend on local

recharge rates)

● Daily Water Requirement of 560 litres for the landscaped

area between 3 piers

● 5.88KL of storage will provide water for about 10 days of

water requirement

MONTH DAYS QUANTITY (mm)

JAN 0.2 2.70

FEB 0.5 7.20

MAR 0.4 4.40

APR 3.0 46.30

MAY 7.0 119.60

JUN 6.4 80.80

JUL 8.3 110.20

AUG 10.0 137.00

SEP 9.3 194.80

OCT 9.0 180.40

NOV 4.0 64.50

DEC 1.7 22.10

TOTAL 59.8 970.00

Rainfall pattern in Bangalore : Westerly Rain30 years data

Rainwater may be insufficient

Proposed Implementation – for every 2 spans

Option 1

(Hard Rock Areas and High Water Table Areas)

● Storage of 15KL

Option 2

(Weathered Rock Areas and Areas where Ground

Water table is 2m below ground level)

● Storage of 8 KL

● Recharge Well of 6.9KL

Proposed Implementation – for every 1 span

Option 1

(Hard Rock Areas and High Water Table Areas)

● Storage of 8 KL

Option 2

(Weathered Rock Areas and Areas where Ground

Water table is 2m below ground level)

● Storage of 4 KL

● Recharge Well of 4KL (3ft diameter and 20ft deep)

Maintenance

● Desilting of Wells once in 5 years● Cleaning of Storage tanks before every rainy season

Open Questions

● RWH Structures to be created for every span or every

alternate span ?

● Location of storage (Above the ground or underground)

● Issues to pile foundations due to recharge wells to be

considered while designing and locating wells

● Place RWH structures based on expected water coming

down each downpipe. All downpipes may not carry equal

volumes of rainwater

Thank You !!

The FIRST METRO in the WORLD to have a comprehensive RWH plan

Storage – Option 3

● Plastic egg crate like reservoir – safe, modular, reusable

(http://sekisui-techno-molding.jp/eng/products/cw/index.html)

Pros

– Safe: Nobody can fall in

– Easy installation

– Modular: Can be used in another location

Cons

– New technology

Recharge Wells in Storm Water Drains

Rainfall Distribution

Rainfall upto X mm No of Days Total Rainfall

80 1 80

60 2 120

30 3 90

25 4 100

20 8 160

10 42 420

TOTAL 60 970