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Catchment Yield Calculator

Work out catchment yield instantly with clear inputs, formula shown and shareable results.

About Catchment Yield Calculator

Catchment yield is rainfall times area times the runoff ratio, which accounts for evaporation, transpiration and deep infiltration. A 45 square kilometre catchment under 900 mm of rain with a 0.35 ratio yields 14.2 million cubic metres a year - a mean flow of 0.45 m3/s. Runoff ratios span 0.1 in dry permeable catchments to 0.7 in wet upland ones.

Formulas

Annual yield

volume = area x rainfall x runoff ratio

Mean flow

flow = annual volume / seconds in a year

Worked example

With the default values below, Catchment Yield Calculator returns Annual Catchment Yield of 1.41750 × 10⁷. Change any input above and every figure here is recalculated in your browser.

Inputs used

Catchment areaminimum 0 km2
45 km2
Annual rainfallminimum 0 mm
900 mm
Runoff ratioaccepts 0–1
0.35

Results

Annual Catchment Yield
1.41750 × 10⁷ m3
Equivalent Mean Flow
0.4492 m3/s
Same Yield In Megalitres
14,175.0
Yield Per Square Kilometre
315.0 ML/km2

Step by step

  1. 1Values used
  2. 2Annual yield
  3. 3Mean flow
  4. 4Annual Catchment Yield= 14,175,000.00000 m3
  5. 5Equivalent Mean Flow= 0.4492 m3/s
  6. 6Same Yield In Megalitres= 14,175.0
  7. 7Yield Per Square Kilometre= 315.0 ML/km2

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax or fees or charges into account.
  • Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

What sets the runoff ratio?

Rainfall intensity and seasonality, soil permeability, vegetation and slope. Upland peat catchments run high, chalk catchments very low.

Is mean flow the same as reliable yield?

No. Reliable yield depends on storage and dry-period flows, and is typically a fraction of the mean.

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