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Calcimator

Dam Spillway Design

Calculate spillway discharge capacity using the weir equation. Determine flow rate, approach velocity, and energy dissipation for dam spillway design.

Inputs

m
m

Results

Spillway Discharge

67.61 m³/s

Discharge (Imperial)

2,387.48 cfs

Daily Discharge5.84 ML/day
Approach Velocity2.25 m/s
Specific Discharge3.38 m³/s/m
Energy Dissipation994.8 kW
How to Use This Calculator
  1. Enter Weir/Spillway Length, Head Over Crest, and Discharge Coefficient (Cd).
  2. Review Spillway Discharge (m³/s) and Discharge (Imperial) (cfs).
  3. Use Daily Discharge (ML/day) and Approach Velocity (m/s) to inform your decision.
  4. Use the chart to visualize the results and explore different scenarios by adjusting inputs.

How the result changes with Head Over Crest

Head Over CrestSpillway DischargeDischarge (Imperial)
2.01104.87 m³/s3,703.37 cfs
7.01683.01 m³/s24,120.17 cfs
131,724.9 m³/s60,914.18 cfs
182,810.33 m³/s99,245.79 cfs

What each input means

Weir/Spillway Length
Effective crest length of the spillway weir in meters
Head Over Crest
Water depth above the spillway crest (excluding velocity head)
Discharge Coefficient (Cd)
Weir coefficient (1.7 = broad-crested, 1.84 = sharp-crested, 2.2 = ogee crest)

How this is calculated

Formula

Q = Cd × L × H^(3/2)

Worked example, using the default values

  1. Identify Input Parameters
    Weir/Spillway Length = 20, Head Over Crest = 1.5, Discharge Coefficient (Cd) = 1.84 = 3 input(s) provided
  2. Calculate Spillway Discharge
    Spillway Discharge
    67.61 = 67.61
  3. Calculate Discharge
    Discharge
    2387.48 = 2387.48
  4. Calculate Daily Discharge
    Daily Discharge
    5.84 = 5.84
  5. Calculate Approach Velocity
    Approach Velocity
    2.25 = 2.25

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

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