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 2-6. Open channel ane,gy ,eletionships

overcome the local energy loss, but the increase will
gradually decrease in the upstream direction. It is this
complication, the freedom in the location of the water
surface, that makes hydraulics of open channels more
complicated and difficult to evaluate than that of closed
conduits.

d. Use in natural rivers. The primary difference
between study methods used for prismatic channels
(channels with an unvarying cross section, roughness,
and bottom slope) and natural rivers results from varia-
tinns in natural river channel cross-sectional shape and
fOUghoeSS and variable bottom slope. Figure 2-7 presents
plan and profile views of a typical study reach for a
natural river and identifies the various classes and types
of flow that may occur within the reach. Note that, not
only can the type of flow vary along a natural channel,
but also the flow regime. Practical application of steady,
one-dimensional flow theory is detailed in Chapter 6.

(1) Figure 2-7 emphasizes that, in natural rivers and
streams, there is rarely uniform flow. Theoretically, a

2.12

complete closed-form solution to the mathematical state-
ment of the balance between the rate of energy loss and
the rate at which it is being added by the drop in the
channel bottom does not exist. Approximations, based
on uniform flow analogies, provide the simplified flow
relationships previously presented for steady gradually
varied flow. The exactness of these approximations is a
function of the accuracy of the channel geometry
measuremenlS, cross-sectional spacing, and, most impor-
tantly, an accurate estimate and use of energy losses.

(2) Other characteristics of flow in natural rivers
must be considered when deciding on an approach 10
take for evaluating river hydraulics problems. The river
engineer must also consider the effects and relative
importance of the steadiness or unsteadiness of the flow
and whether a one-dimensional approximation of the flow
will provide sufficient accuracy and detail for the particu-
lar flow and channel configuration.

e. Unsteady flow.
discussions regarding

Chapter 5 presents detailed
typical data and computer

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