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Dams Spillway Flow Calculator

Fluids Engineering and Design
Civil Engineering and Design

Dam’s Spillway (overflow spillway) Flow Formula and Calculator

A dam’s spillway (overflow spillway) is designed for a capacity based on the dam’s inflow hydrograph, turbine capacity, and storage capacity. Spillways frequently have a cross section known as an ogee, which closely approximates the underside of a nappe from a sharpcrested weir. This cross section minimizes the cavitation that is likely to occur if the water surface breaks contact with the spillway due to upstream heads that are higher than designed for.

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Discharge from an overflow spillway is derived in the same manner as for a weir. Equation 1 can be used for broad-crested weirs (C1 = 0.5–0.57) and ogee spillways (C1 = 0.60–0.75).

Eq. 1,
Q = 2/3 C1 b (2g)0.5 H3/2

Where:

H = height, m
b = width of weir, m
Q = Flow, m3/s
g = gravity, 9.81 m/s2
C1 = discharge coefficient

Reference:

  • Civil Engineering Reference Manual, Fifteeth Edition

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