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River Discharge Calculator

Work out river discharge instantly with clear inputs, formula shown and shareable results.

About River Discharge Calculator

Discharge is cross-sectional area times mean velocity: 12 m wide, 1.4 m deep and 0.85 m/s gives 14.28 m3/s, or 1.23 million cubic metres a day. Mean velocity is normally about 0.85 of the surface velocity, and in practice it is measured at six-tenths depth across several verticals.

Formulas

Discharge

Q = A x v = width x depth x mean velocity

Surface velocity correction

mean velocity is about 0.85 x surface velocity

Worked example

With the default values below, River Discharge Calculator returns River Discharge of 14.280. Change any input above and every figure here is recalculated in your browser.

Inputs used

Channel widthminimum 0 m
12 m
Average depthminimum 0 m
1.4 m
Mean velocityminimum 0 m/s
0.85 m/s

Results

River Discharge
14.280 m3/s
Cross-Sectional Area
16.80 m2
Same Discharge In Litres Per Second
14,280
Volume Passing Per Day
1,233,792 m3

Step by step

  1. 1Values used
  2. 2Discharge
  3. 3Surface velocity correction
  4. 4River Discharge= 14.280 m3/s
  5. 5Cross-Sectional Area= 16.80 m2
  6. 6Same Discharge In Litres Per Second= 14,280
  7. 7Volume Passing Per Day= 1,233,792 m3

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, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 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

Where should velocity be measured?

At 0.6 of the depth from the surface for a single reading, or averaging 0.2 and 0.8 depth readings for better accuracy.

Why does discharge matter more than depth?

Because it measures the water actually delivered. Depth alone says nothing without width and velocity.

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