# 5: Open-Channel Flow

- Page ID
- 4175

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This chapter is a selective presentation of some important topics in free- surface flow. I will defer consideration of the generation and propagation of gravity waves on the free surface of a standing or flowing body of liquid until Chapter 6, on oscillatory flow.

- 5.1: Introduction to Open-Channel Flow
- Open-channel flows are those that are not entirely included within rigid boundaries; a part of the flow is in contract with nothing at all, just empty space. The surface of the flow thus formed is called a free surface, because that flow boundary is freely deformable, in contrast to the solid boundaries. The boundary conditions at the free surface of an open-channel flow are always that both the pressure and the shear stress are zero everywhere.

- 5.2: Two Practical Problems
- One of the interesting things about open-channel flow is the effect of gravity on the shape of the free surface relative to the solid boundary. All open-channel flow, even broad, majestic rivers like the Mississippi, or flows in laboratory channels we try to keep as nearly uniform as possible, are subject to such effects of gravity.

- 5.3: Uniform Flow
- Uniform flow serves as a good reference case from which to think about the effect of gravity on the free surface in an open-channel flow. Only if an open- channel flow can somehow be adjusted to be strictly uniform, in the sense that the water surface is planar and the flow depth is the same at all cross sections along the flow, can the effect of gravity in shaping the flow be ignored.

- 5.4: Energy in Open-Channel Flow
- To address the two channel-transition problems posed earlier, we need to have a closer look at mechanical energy in an open-channel flow, and at how the partitioning of the various components of that mechanical energy, kinetic and potential, are changed at the transition in question.