Ecology & Environment
Rain Garden Runoff Storage Planner Calculator
Translate contributing area and design runoff depth into net captured volume, gross storage demand, whole storage modules if used, annualized volume, and budget use.
Net quantity reaching target-
Quantity adjusted for efficiency-
Gross quantity per application-
Annual gross quantity-
Whole packages per application-
Whole packages per year-
Annual material cost-
Annual cost per treated area-
Budget remaining after modeled cost-
Share of annual budget used-
Decision view
Contributing surface, inlet, and rain-garden basin
Contributing surface, inlet, and rain-garden basinRunoff from the connected surface enters temporary ponding storage while soil media and overflow reserve remain visible.
Exact scenario comparisonBase cubic feet per area unit changes while all other entered assumptions remain constant.
| Base cubic feet per area unit | Net quantity reaching target | Quantity adjusted for efficiency | Gross quantity per application | Annual gross quantity | Whole packages per application | Whole packages per year | Annual material cost | Annual cost per treated area | Budget remaining after modeled cost | Share of annual budget used |
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How to use Rain Garden Runoff Storage Planner Calculator
- Use the roof or pavement area that actually drains to the garden.
- Enter the design runoff depth on a consistent area-volume basis.
- Compare gross storage with basin geometry, outlet, overflow, soil, and setback constraints.
Calculator guide
Understanding Rain Garden Runoff Storage Planner Calculator
A rain garden must temporarily store runoff from a defined contributing area while accounting for capture efficiency, overflow allowance, and the usable depth of the basin.
Calculation method
How the calculation works
Calculate net rain-garden storage need from treated area and the entered rate, gross it up for application efficiency and field loss, round purchase packages upward, and reconcile annual quantity, cost, and budget use. Contributing area times runoff depth gives net target storage; efficiency and field loss raise the gross capacity required.
Runoff route
Follow roof runoff into the planted basin
The cross-section distinguishes contributing surface, inlet, temporary ponding, soil media, and overflow reserve.
Worked situations
Practical examples
- Disconnecting part of a roof reduces the contributing area.
- A lower capture efficiency increases gross basin capacity needed for the same net capture.
- Whole modules may represent crates or manufactured storage cells beneath the soil profile.
Better inputs
Useful tips
- Confirm unit conversions between rainfall depth, area, and cubic volume.
- Reserve freeboard above the design storage level.
- Check infiltration rate and drawdown time with site-specific soil information.
Before relying on the result
Limitations and common mistakes
- The model does not perform a storm hydrograph, infiltration test, routing analysis, or overflow design.
- Groundwater, utilities, slopes, setbacks, and local stormwater rules may control feasibility.
- Professional drainage design may be required.
Reference
Key terms
- Contributing area
- Surface area routed into the rain garden.
- Design storage
- Temporary volume required for the selected runoff event.
- Freeboard
- Vertical reserve above the modeled water level.
Important note
Calculated from the entered environmental values using the displayed model. Measurement quality, local conditions, system boundaries, and source data affect interpretation.
Frequently asked questions
Does the result include infiltration during the storm?
Only indirectly through the entered efficiency assumptions; no hydrograph is routed.
Can annual applications represent annual storms?
Yes, for an annualized volume illustration, not for regulatory sizing.
Is the calculated volume the excavation volume?
Not necessarily. Side slopes, soil media, stone voids, and freeboard change excavation.