Indian High-Rise Stormwater Management — CPHEEO 2019 + CGWB + SuDS
By MEPVAULT Editorial Team · MEP Consultant · Plumbing / Sustainability · 11 May 2026
Reading time ~ 9 min · Originally published: 03 May 2026 · Last revised: 11 May 2026
For a 5,000 m² Bengaluru commercial plot, design rainfall 90 mm/hr produces 75 L/s peak runoff against a 40 L/s municipal drain capacity. The 35 L/s excess requires a 130 m³ HDPE detention tank + 50 m³ RWH tank + 8 m³ soakaway + bioswales — the CPHEEO 2019 sustainable urban drainage stack. Without this on the design submission, the AHJ does not issue an occupancy certificate. Three site failures: 2-yr vs 25-yr sizing, silted soakaway, missing first-flush diverter.
Indian high-rise stormwater — what the new CPHEEO 2019 Manual demands
The 2019 CPHEEO Storm Water Drainage Manual replaced the 1995 edition with a sustainable-urban-drainage (SuDS) framework. For any Indian urban plot above 300 m², the manual now requires on-site stormwater detention + recharge calculation in the design submission. Without it, the AHJ does not issue an occupancy certificate. Many developers still treat stormwater as a “discharge to municipal drain” problem — that approach has been non-compliant since 2019.
Runoff calculation — the rational method
| Surface type | Runoff coefficient C | Practical implication on 1000 m² site | Drainage requirement |
|---|---|---|---|
| Concrete + asphalt road | 0.85-0.95 | High runoff, fast peak | Underground RCC drain DN 300+ |
| Tiled rooftop / metal sheet | 0.85-0.95 | Same — but harvestable for RWH | Roof drain + downpipe + RWH inlet |
| Compacted earth / gravel | 0.40-0.60 | Moderate runoff | Open channel or perforated pipe |
| Pervious paving (block / grass) | 0.20-0.35 | Low runoff, slow peak | Sub-base recharge |
| Grassed area / garden | 0.05-0.25 | Very low — most water absorbed | Surface drainage only |
| Bioswale / rain garden | -0.10 to 0.10 | Net infiltration | Soak away zone |
A 5000 m² Bengaluru commercial plot — stormwater design walkthrough
Bengaluru design rainfall intensity 90 mm/hr × 1-hour duration (2-year return period per IMD).
| Surface | Area (m²) | C | Effective runoff area (m²) |
|---|---|---|---|
| Tiled rooftop | 2,000 | 0.90 | 1,800 |
| Hardstanding / driveway | 800 | 0.90 | 720 |
| Block paving | 1,000 | 0.30 | 300 |
| Landscape / garden | 1,200 | 0.15 | 180 |
| Total | 5,000 | — | 3,000 m² effective |
| Step | Value | Source |
|---|---|---|
| Peak runoff rate (Q = C×I×A) | 3000 m² × 90 mm/hr ÷ 3600 | 75 L/s |
| Receiving municipal drain capacity | 40 L/s (limit set by local body) | — |
| Storage required (excess flow × duration) | 35 L/s × 60 min = 126 m³ | calc |
| Stormwater detention tank | 130 m³ HDPE underground | design |
| RWH harvesting from 2000 m² roof | 2000 × 0.9 × 0.97 m (annual rainfall) × 0.7 C = 1,222 m³/yr | IS 15797 |
| RWH storage tank | 50 m³ | flushing + irrigation demand |
| Excess overflow path | Slow release to detention then to municipal drain | design |
| Recharge pit / soakaway | 8 m³ in pervious-paving sub-base | CGWB design |
Sustainable urban drainage (SuDS) components for Indian projects
- Pervious paving — 40-60 % of hardstanding can be pervious blocks (concrete-grid + grass-filler or porous concrete). Cuts runoff coefficient from 0.90 to 0.30. Cost premium ~30 % vs solid paving; pays back in reduced storm drain sizing.
- Bioswales — landscaped depressions along driveways + parking edges. Slow water + recharge. Native Indian species (kasturi grass, vetiver) thrive without irrigation.
- Detention tank (underground) — sized for the excess between peak runoff and municipal drain capacity. HDPE prefab tanks or RCC sumps. Slow-release orifice keeps outflow at municipal limit.
- Recharge pit / soakaway — 1.5-2 m diameter × 3-5 m deep, filled with stone pitching + perforated pipe. Per CGWB Master Plan, mandatory for plot > 300 m² in CGWB notified zones (Mumbai, Pune, Bengaluru, Delhi NCR, Chennai).
- Rainwater harvesting (RWH) — separate from detention; captures clean roof runoff for reuse. Sized for flushing + irrigation + cooling-tower-makeup demand.
Three failures we catch on Indian high-rise stormwater
- Detention sized for 2-year rainfall, ignoring climate trends — Mumbai 2005 and 2017 floods showed 100-year+ events. Size for 25-year minimum, even though manual says 2-year.
- Soakaway clogged within 18 months — without a sediment trap upstream, soakaway fills with silt and stops infiltrating. Always specify a desilting chamber + maintenance schedule.
- RWH first-flush diverter missing — first 2-3 mm of rainfall carries roof dust + bird droppings + acid deposits. Without a first-flush diverter, this contaminates the RWH storage. ₹5,000-15,000 device that gets value-engineered out — restore on every BoQ.
References
- CPHEEO Manual on Storm Water Drainage Systems (3rd edition), Ministry of Housing and Urban Affairs GoI 2019.
- CGWB Master Plan for Artificial Recharge to Ground Water in India 2020, Ministry of Jal Shakti GoI.
- IS 15797:2008 — Roof-top Rainwater Harvesting — Guidelines, Bureau of Indian Standards.
- IMD Hydrological Atlas of India 2022 — return-period rainfall intensities by city.
- USEPA SWMM (Storm Water Management Model) Reference Manual v5.2 — runoff calculations.
- UK CIRIA Manual C753 — The SUDS Manual 2015 (referenced for sustainable urban drainage).
- NBC 2016 Part 9 Section 3 — Drainage and Sanitation (storm water section).
- IGBC Green New Buildings v3.0 — SE-2 Rainwater Management credit.
// About the Authors
MEPVAULT Editorial Team — A team of practising MEP consultants based in India. ISHRAE-affiliated; FSAI-aligned.