OPEN CHANNEL FLOW Any liquid flowing in a conduit or channel that is not completely filled and sealed (open to atmosphere) is considered an open channel flow Fluid Mechanics [ physical interpretation: what are we doing today? ] Typically these flows are driven purely by gravity as no pressure gradient can be applied while the flow is totally open to the atmosphere For a fully developed, steady, open channel flow the pressure distribution is essentially hydrostatic flow through creeks, streams, rivers, and drainage channels are all open channel flow examples, without these flows we would not be here Who Cares!? Steady, fully developed flows develop a balance between the shear force resisting the fluid flow over the channel surface and the fluid weight force OPEN CHANNEL FLOW [ physical interpretation: examples of open channel flow ] Fluid Mechanics The range of values the geometric variables can take in an open channel problem usually prohibit the use of any straightforward analytical approach, therefore scaled physical models are usually developed The existence of a free-surface in open channel flow means that the flow is free to assume many different forms that are not possible in pressurized pipe flow, this further complicates OC flow analysis As in closed conduit flows, open channel flows can classified as laminar or turbulent, steady or unsteady, we will only examine steady OC flows OPEN CHANNEL FLOW OC flows can be further classified by observing the manner in which the fluid depth, y, varies with distance along the channel, x. [ fundamentals ] Fluid Mechanics A uniform open channel flow is classified as one where the depth does not vary along the channel (dy/dx=0) When dy/dx 0, the OC flow is called non uniform Non-uniform flows may have flow depths that vary considerably over a short distance, these are called rapidly varying flows (RVF) (dy/dx~1), if the depth changes slowly with distance this is referred to as a gradually varying flow (GVF) (dy/dx