Free surface flow is primarily driven by the force of gravity, which causes the fluid to flow from higher elevations to lower elevations.

The defining characteristic of free surface flow is the presence of a free surface, which is the interface between the fluid and the atmosphere.

Bernoulli's Equation is used to describe the flow of an ideal fluid in an open channel. It relates the pressure, velocity, and elevation of the fluid along a streamline.

Backwater Curve is the term used to describe the gradual increase in the depth of flow as it approaches an obstruction in an open channel.

Hydraulic Jump is the phenomenon where a rapidly flowing stream of fluid suddenly changes to a slower, deeper flow.

The Froude Number is used to determine the type of flow pattern in an open channel, whether it is subcritical, critical, or supercritical.

Weirs, orifices, and sluice gates are all common types of hydraulic structures used to control the flow of water in an open channel.

The specific energy of a fluid flowing in an open channel is defined as the sum of the potential energy and kinetic energy per unit weight of fluid.

The critical depth of flow in an open channel is the depth at which the Froude Number is equal to one.

In a gradually varied flow, the water surface profile is curved.

The Manning's Equation is commonly used to calculate the velocity of flow in an open channel.

The Chezy's Equation is an alternative formula for calculating the velocity of flow in an open channel.

The Darcy-Weisbach Equation is used to calculate the head loss due to friction in a pipe.

The Moody Diagram is a graphical representation of the friction factor for pipe flow.

The Reynolds Number is a dimensionless parameter used to characterize the flow regime in a pipe.