FLOOD01888

• County: Statewide
• Title: River Hydraulics
• Date: 10/15/1993
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Educational/Technical/Reference Information

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EM 1110-2.1416
15 Oct 93

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Figure 2-4. Some types of open-chennel flow

what methods may be appropriate for any particular
study.

2.7. Classification of Flow Profiles

The following classification of steady flow water surface
proftles follows that of Chow (1959). This assumes a
one-dimensional condition.

a. Channel slope. Channel slope is one criterion
used to classify steady flow profiles. A critical slope is
one on which critical velocity is sustained by a change in
potential energy rather than pressure head. A mild slope
is less than critical slope, and a steep slope is greater
than critical slope for a given flow. When the slope is
positive, it is classified as mild, steep, or critical, and the
corresponding flow profiles are the M, S, or C profiles,
respectively (see Figure 2-5). If the slope of the channel
bed is zero, the slope is horizontal and the profiles are
called H profiles. If the bed rises in a downstream direc-
tion, the slope is negative and is called an adverse slope,
producing A proftles.

b. Normal and critical depths. Another parameter
used to classify gradually varied flow proftles is the
magnitude of the water depth relative to normal depth,
D n' and critical depth, Dc' The depth that would exist if
the flow were uniform is called normal depth. Critical
depth is that for which the specific energy for a given
discharge is at a minimum. Specific energy is defined
as:

He

2
= d + aV
2g

(2-3)

where

d = depth of flow (ft)
a = energy correction factor (dimensionless)
V212g = velocity head (ft)

2-8. Basic Principles of River Hydraulics

a. Conservation of mass. Evalualion of the hydrau-
lic characteristics of rivers and open channels requires

2.9