Rain Basin Storage and Infiltration Calculator
Solve an ideal basin plan area from separate catchment runoff, direct rainfall, constant infiltration and entered storage depth.
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Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Balance catchment run-on plus direct rainfall on the unknown basin against storm infiltration plus end storage.
Basin area=catchment area×runoff fraction×rain / (storage depth+infiltration×duration−rain)
Worked example
100 m² catchment, runoff fraction 0.8, rainfall 30 mm, one-hour infiltration at 10 mm/h and stored depth 150 mm give ideal basin area 2.4/0.13≈18.4615 m².
Assumptions and input details
Assumes constant runoff intensity, immediate infiltration and an initially empty uniform basin; contributing catchment excludes basin footprint. Infiltration and depth must use the same length/time basis. The denominator must be positive when run-on is positive. This simplified water balance does not establish site suitability, flood protection, groundwater separation, setbacks, overflow routing or regulatory compliance. Real soil/antecedent conditions require separate assessment.
References: EPA: bioretention/rain-garden context and design variability
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
Choose from 23 length definitions, including explicitly labelled regional measures. Area conversions square the length factor; geometric volumes cube it.
Regional measures are not interchangeable merely because their names look similar. This is a documented selection, not a claim to include every historical unit.
NIST measurement tables · Japanese traditional units · Mainland China and Hong Kong unit distinctions
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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