According to the Darcy-Weisbach equation for head loss due to pipe friction:

Since the two pipes are similar (identical friction factor $f$, length $L$, and diameter $D$), the head loss is directly proportional to the square of flow velocity ($h_f \propto V^2$):

Froude number ($Fr$) is a dimensionless parameter defined as the square root of the ratio of inertia force to gravity force:

Where $V$ is flow velocity, $g$ is acceleration due to gravity, and $D$ is hydraulic depth. It governs open channel flow regimes (subcritical $Fr \lt 1$, critical $Fr = 1$, supercritical $Fr \gt 1$). Reynolds number is inertia force to viscous force; Mach number is inertia force to elastic force; Euler number is inertia force to pressure force.

Classification of fluid flow in hydraulics:
Steady flow: Flow parameters (velocity, depth) do not change with time at any given cross-section ($\partial V/\partial t = 0, \partial y/\partial t = 0$) -> (III).
Uniform flow: Flow parameters (velocity, depth) do not change along the length/space at any given instant ($\partial V/\partial s = 0$) -> (IV).
Non-uniform flow: Velocity changes from point to point along the length of flow ($\partial V/\partial s \ne 0$) -> (I).
Unsteady flow: Velocity and depth change with time at a given cross-section ($\partial V/\partial t \ne 0$) -> (II).