RWH for Bangalore Metro

Rainwater Harvesting for the Bangalore METROBiome 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

OverviewName Area RemarksViaduct 35 kms in Effective length and 10 catchment metres in above ground width level Landscaped 30 kms in Only whereArea length and there is a 2.5m in width median, below the via- excluding duct 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

Rainfall pattern in Bangalore : Westerly Rain30 years data 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

RWH PotentialCatchment description Area Annual Run- Run off for 30 Run off for 60 mm (sqm) off 970mm mm rain in KL rain in KL (heavy (KL) (average rain) rain)Total proposed length of 350000 305550 9450 18900METRO above ground level(35km length * 10m width)One span 280 244 8 15(Distance between 2 piers)(28m length * 10m width)Two spans 560 489 15 30(Distance between 3 piers)(56m length * 10m width) Annually: 300 Million litres Bangalore Daily Water Requirement : 1500MLPD

Landscaping detailsImportant 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 RequirementsLandscaped Area Area Daily Water Annual WaterDescription (sqm) Requirement Requirement (litres) @ 4l/sqm (KL) 300 daysMedian below Total proposed 75,000 3,00,000 90,000length of METRO(30km length * 2.5m width)Median below One span 70 280 84(Distance between 2 piers)(28m length * 2.5m width)Median below Two spans 140 560 168(Distance between 3 piers)(56m length * 2.5m width) Annually: 90 Million litres

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)

Storage – Option 2Pre Cast Concrete Tanks

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 making of a recharge well Pit and concrete rings The pit has reach the silt layer Placing of the rings

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 6.9KLstatic storage (effective capacity will depend on localrecharge rates)● Daily Water Requirement of 560 litres for the landscapedarea between 3 piers● 5.88KL of storage will provide water for about 10 days ofwater requirement

Rainfall pattern in Bangalore : Westerly Rain 30 years data 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 Rainwatermay be insufficient 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

Proposed Implementation – for every 2 spansOption 1(Hard Rock Areas and High Water Table Areas) ● Storage of 15KLOption 2(Weathered Rock Areas and Areas where GroundWater table is 2m below ground level) ● Storage of 8 KL ● Recharge Well of 6.9KL

Proposed Implementation – for every 1 spanOption 1(Hard Rock Areas and High Water Table Areas) ● Storage of 8 KLOption 2(Weathered Rock Areas and Areas where GroundWater table is 2m below ground level) ● Storage of 4 KL ● Recharge Well of 4KL (3ft diameter and 20ft deep)

Maintenance● Desilting of Wells once in5 years● Cleaning of Storagetanks before every rainyseason

Open Questions● RWH Structures to be created for every span or everyalternate span ?● Location of storage (Above the ground or underground)● Issues to pile foundations due to recharge wells to beconsidered while designing and locating wells● Place RWH structures based on expected water comingdown each downpipe. All downpipes may not carry equalvolumes of rainwater

The FIRST METRO in the WORLD to have acomprehensive RWH plan Thank You !!

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 DistributionRainfall upto X mm No of Days Total Rainfall80 1 8060 2 12030 3 9025 4 10020 8 16010 42 420TOTAL 60 970

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RWH for Bangalore Metro

by biomeshubha

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