Post on 23-Jun-2015
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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