What is the difference between an open channel flow and shee

Solution

I have listed the main differences between open channel flow & sheet flow in overland. These are,

1) Definition: Starting with definition, open channel is a flow in which fluid flow with a free surface open to the atmosphere. For example rivers, canals , streams etc. Now coming to overland sheet flow, it is a special type of open channel flow which generally occur in urban watershed impervious layers such as roofs, parking lots as well as pervious layers such as lawn.

2) Depth: The most important difference is depth. Sheet flow is a shallow depth flow which has a depth of few inches whereas open channels have depth in feet.

3) State of Flow: Depending upon the characteristics of flow, open channel can be classified as laminar, transisition or turbulent. But in case of sheet flow, the reynolds number is low because depth of flow is very less. There based on this, sheet flow should be classified as open channel flow, however many factors affects sheet flow like obstruction due to grass, rainfall impact etc. which cause the flow turbulent dispite having low reynolds number.

4) Mannings coefficient (n): The mannings coeff. used for overland sheet flow are slightly different than open channel flow. This is because the mannings coeff. for sheet flow also accounts disturbance due to fator like grass, rock, litter, rainfall impacts, erosion, trabsortation of sediments and surface drag & therefore effective manning coeff. is used.

However all equations applicable to open channel flow are also appliable for sheet flow.