Open channel flow has a free water surface which is NORMALLY subject to the atmospheric pressure.

Steady open channel flow : In this case the discharge and water depth at any section in the reach do not change with time during the PERIOD of interest.

Unsteady open channel flow : In this case the discharge and the water depth at any section in the reach change with time.

Uniform open channel flow : In this case the discharge and the water depth remain the same in energy section in the channel reach. It is mostly steady.

Varied open channel {low : In this case the water depth and/or the discharge change along the length of the channel. It may be steady (such as flow over a spillway crest) or unsteady (as in the case of FLOOD waves or TIDAL surge).

Open channel flow has a free water surface which is normally subject to the atmospheric pressure.

Steady open channel flow : In this case the discharge and water depth at any section in the reach do not change with time during the period of interest.

Unsteady open channel flow : In this case the discharge and the water depth at any section in the reach change with time.

Uniform open channel flow : In this case the discharge and the water depth remain the same in energy section in the channel reach. It is mostly steady.

Varied open channel {low : In this case the water depth and/or the discharge change along the length of the channel. It may be steady (such as flow over a spillway crest) or unsteady (as in the case of flood waves or tidal surge).