FLOOD01169

• County: Statewide
• Community: State of Colorado
• Stream Name: All
• Title: Design Guidelines and Criteria Channels and Hydraulic Structures on Sandy Soil
• Date: 6/1/1981
• Prepared For: UDFCD
• Prepared By: Simons Li & Associates Inc.
• Floodplain - Doc Type: Educational/Technical/Reference Information

48

.

where, Y 1

the upstream flow depth,

a

= the embankment length measured normal to the bank,

.

Frl = the upstream Froude number.

If the embankment terminates at a vertical wall on the upstream side, then

the scour depth in sand nearly doubles. That is,

.

Y
s
~-

2.15 (

a
Yl

)0.40 FrlO.33

(3-8)

Field data for scour at embankments for various size rivers is scarce, but .
data collected at rock dikes on the Mississippi River indicate that
Y
s 4 Frl (3-9)
~-
.

determines the equilibrium scour depth for large a/Y l' It is recommended

that Equations 3-7 and 3-8 be applied to embankments with 0 < a/Yl < 25 and

Equation 3-9 be used for a/Yl > 25. If a/Yl > 25, then scour depth is

independent of a/Yl and depends only on the approach Froude number and

depth of flow.

.

In applying Equations 3-7 and 3-8, the embankment length a is measured

.

from the high waterline at the valley bank perpendicularly to the end of the

embankment. A definition of the embankment length for a natural channel with

riprap protection is shown in Figure 3-2. It is not uncommon to find depths

.

to be 30 percent greater than equilibrium scour depth. Lateral extent of

scour can be determined from the angle of repose of the material and scour

depth. .

3.7.2 Local Scour Downstream of Hydraulic Structures

The scour downstream of hydraulic structures, such as stilling basins,

.

diversion works, and etc., occurs frequently in engineering application.

Figure 3-3 summarizes the possible flow condHions downstream of hydraulic

.