The Mulvaney Equation was proposed by the Irish engineer Thomas James Mulvaney (1822-1892). The equation was first published in 1851. The model predicts the peak discharge $Q$ as a function of an empirical constant $C$, the average rainfall intensity of the catchment $I$ and the area of the catchment $A$:

$$Q [m^3/s] = C [10^3*86400/10^6] * I [mm/hour] * A [km²]$$

The intensity being given in mm/hour and the area in km², the constant $C$ needs to perform the transformation of units from mm/hour and km² to m³/s. This equation is only valid for small catchments in which storage and losses are not significant.

This equation in SI units reads:

$$Q_{peak} = 0.278 * C * I * A$$

where

$Q_{peak}$ = peak discharge in cubic meters per second

$I$ = Intensity of rainfall in mm/hour

$A$ = Area in square kilometers

$C$ is a runoff coefficient.