CivilTech Studio
Rainwater Harvesting Recharge Pit
Size a rooftop rainwater recharge pit from roof area, rainfall and soil infiltration — to CGWB guidelines and IS 15797.
- Annual harvest
- Peak-storm sizing
- Infiltration-governed
- Silt-trap & overflow notes
- CGWB Guidelines
- IS 15797:2008
- Rational method
What it does
Everything the check needs, in one pass
Estimate the annual harvest and the peak storm inflow from a roof, then size a recharge pit so the soil infiltration can drain the design storm without overflowing — using the rational method and CGWB recharge guidance.
Annual harvest
Computes the harvestable volume from roof area, rainfall and the runoff coefficient.
Peak-storm sizing
Sizes the pit for the design storm inflow versus the soil infiltration rate.
Infiltration-governed
Pit base area is driven by the saturated soil percolation rate, not a rule of thumb.
Silt-trap & overflow notes
Flags the desilting chamber and overflow needed for a maintainable pit.
How it works
From inputs to a signed-off result
- Step 1
Enter the catchment
Roof area, annual rainfall and the runoff coefficient.
- Step 2
Set the storm & soil
Peak rainfall intensity and the soil infiltration rate.
- Step 3
Size the pit
The tool balances inflow against infiltration to find the pit dimensions.
- Step 4
Review harvest & pit
Annual harvest, peak inflow and pit length × width × depth.
Standards
Checked against the code, clause by clause
Every result cites the clause it came from, so a reviewer can follow the same path you did.
CGWB Guidelines
Artificial recharge / recharge-pit sizing
IS 15797:2008
Roof rainwater harvesting
Rational method
Peak runoff Q = C·i·A
Who it’s for
Where engineers reach for it
Residential rooftop
A house roof recharging a single soak pit.
Large terrace, clay soil
Low infiltration drives a larger pit base.
Campus / institutional
A bigger catchment harvesting to multiple pits.
Groundwater recharge mandate
Meeting a municipal rainwater-harvesting requirement.
FAQ
Questions, answered
Something else? Open Rainwater Harvesting Pit and try it with your own numbers.
How is the pit size decided?
By balancing the design-storm inflow (rational method) against the soil infiltration rate, so the pit stores only what has not yet infiltrated.
What infiltration rate should I use?
Use the saturated (long-term) percolation rate, not the initial dry rate — designing for the dry rate undersizes the pit.
Do I need a silt trap?
Yes — a desilting chamber keeps fines out of the pit; without it the infiltration rate drops and the pit clogs.
What about storms larger than design?
Provide an overflow; the tool flags it so rare events above the design storm do not flood the area.
How much water will I harvest?
The annual harvest = roof area × annual rainfall × runoff coefficient, reported in litres and m³.
Open Rainwater Harvesting Pit and run your numbers
Size a rooftop rainwater recharge pit from roof area, rainfall and soil infiltration — to CGWB guidelines and IS 15797.
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