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Calcimator

Whitewater Flow Calculator

Evaluate river flow conditions for paddling suitability using flow rate, width, and depth to calculate velocity, Froude number, and feature suitability.

Inputs

Results

Flow velocity (ft/s)

2.78

Froude number0.28
Flow per ft width (cfs/ft)8.3
Feature suitability (0-100)28
Estimated whitewater class1
How to Use This Calculator
  1. Look up the current flow rate in cfs from a USGS stream gauge for your river section.
  2. Measure or estimate the average river channel width in feet at the feature you are evaluating.
  3. Estimate the average water depth in feet across the channel.
  4. Select the type of feature you are assessing: surfing wave, play hole, eddy lines, or general class run.
  5. Read Flow Velocity (ft/s) and Froude Number — a Froude number above 1 indicates supercritical (fast, steep) flow.
  6. Check Feature Suitability Score (0–100) and Estimated Whitewater Class to decide if current conditions match your skill level.

How the result changes with Flow rate (cfs)

Flow rate (cfs)Flow velocity (ft/s)
10,00055.56
35,000194.44
65,000361.11
90,000500

What each input means

Flow rate (cfs)
River discharge in cubic feet per second. Check USGS gauges for real-time data.
River width (ft)
Average width of the river channel at the feature.
Average depth (ft)
Average water depth across the channel.
Feature Type
Type of whitewater feature to evaluate.

What each result means

Flow velocity (ft/s)
Water speed calculated from flow rate and cross-section.
Froude number
Dimensionless ratio indicating flow regime. <1 subcritical, >1 supercritical.
Flow per ft width (cfs/ft)
Flow concentration — useful for comparing different rivers.
Feature suitability (0-100)
How suitable current flow is for the selected feature type.
Estimated whitewater class
Rough whitewater difficulty class (I-V) based on flow dynamics.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Flow rate (cfs) = 500, River width (ft) = 60, Average depth (ft) = 3, Feature Type = 1 = 4 input(s) provided
  2. Calculate Flow velocity
    Flow velocity = flowRateCfs / crossSection
    2.78 = 2.78
  3. Calculate Froude number
    Froude number = velocity / sqrt(g * avgDepthFt)
    0.283 = 0.283
  4. Calculate Flow per ft width
    Flow per ft width = flowRateCfs / riverWidthFt
    8.3 = 8.3

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

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