Description
Multiply roofArea by contributionFraction for contributingArea, then by rainfallDepth and runoffFraction for runoffVolume.
A runoff-volume term multiplies catchment area by rainfall depth and explicit contribution factors. It represents one supplied event scenario rather than a drainage-system design.
Multiply roofArea by contributionFraction for contributingArea, then by rainfallDepth and runoffFraction for runoffVolume.
When to use this tool
Use Rain Chain Catchment Contribution Term when you need a catchment contribution under stated rainfall and runoff assumptions.
How to use the tool and how it works
- Enter roofArea, contributionFraction, rainfallDepth, runoffFraction. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read contributingArea, runoffVolume. Use the output convention below.
Multiply roofArea by contributionFraction for contributingArea, then by rainfallDepth and runoffFraction for runoffVolume.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| roofArea | Roof Area | Required. Finite number; minimum 0. |
| contributionFraction | Contribution Fraction | Required. Finite number; minimum 0; maximum 1. |
| rainfallDepth | Rainfall Depth | Required. Finite number; minimum 0. |
| runoffFraction | Runoff Fraction | Required. Finite number; minimum 0; maximum 1. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| contributingArea | Contributing Area | Required. Finite number. |
| runoffVolume | Runoff Volume | Required. Finite number. |
{
"input": {
"roofArea": 100,
"contributionFraction": 0.25,
"rainfallDepth": 0.02,
"runoffFraction": 0.8
},
"output": {
"contributingArea": 25,
"runoffVolume": 0.4
}
}Limitations and assumptions
- Use coherent area and depth units; fractions are supplied event assumptions rather than a rainfall forecast or hydraulic design.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.
Alternative or Complementary methods
Use a local hydrologic and hydraulic analysis for rainfall selection, infiltration, routing, and drainage capacity.
References
Similar or alternative tools
- Irrigation Zone Overlap Area Correction
Subtract overlap from firstArea + secondArea for unionArea.
- Rain Garden Ponding Volume Term
Return depth × (bottomArea + topArea + sqrt(bottomArea × topArea)) / 3, requiring topArea at least bottomArea.