Unformatted text preview: concepts
from steady duct flow—hydraulic diameter, friction factor, head losses—apply also to
open channels. 10.1 Introduction Simply stated, open-channel flow is the flow of a liquid in a conduit with a free surface. There are many practical examples, both artificial (flumes, spillways, canals, weirs,
drainage ditches, culverts) and natural (streams, rivers, estuaries, floodplains). This
chapter introduces the elementary analysis of such flows, which are dominated by the
effects of gravity.
The presence of the free surface, which is essentially at atmospheric pressure, both
helps and hurts the analysis. It helps because the pressure can be taken constant along
the free surface, which therefore is equivalent to the hydraulic grade line (HGL) of the
flow. Unlike flow in closed ducts, the pressure gradient is not a direct factor in openchannel flow, where the balance of forces is confined to gravity and friction.1 But the
free surface complicates the analysis because its shape is a priori unknown: The depth
profile changes with conditions and must be computed as part of the problem, especially in unsteady problems involving wave motion.
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This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.
- Spring '08