TM 5-820-3/AFM 88-5, Chap. 3
c. Empirical equations have been developed for
in terms of discharge parameter for estimating the
estimating the extent of the anticipated scour hole
extent of localized scour to be anticipated down-
in sand, based on knowledge of the design dis-
stream of culvert and storm drain outlets. The
charge, the culvert diameter, and the duration and
equations for the maximum depth, width, length,
Froude number of the design flow at the culvert
and volume of scour and comparisons of predicted
outlet. However, the relationship between the
and observed values are shown in figures 5-4
Froude number of flow at the culvert outlet and a
through 5-7. Minimum and maximum tailwater
discharge parameter, or Q/Do5/2, can be calculated
depths are defined as those less than 0.5Do and
for any shape of outlet, and this discharge parame-
equal to or great than O.5Do, respectively. Dimen-
ter is just as representative of flow conditions as is
sionless profiles along the center lines of the scour
the Froude number. The relationship between the
holes to be anticipated with minimum and maxi-
two parameters, for partial and full pipe flow in
mum tailwaters are presented in figures 5-8 and 5-
square culverts, is shown in figure 5-3. Terms are
9. Dimensionless cross sections of the scour hole at
defined in appendix E. Since the discharge param-
a distance of 0.4 of the maximum length of scour
eter is easier to calculate and is suitable for appli-
downstream of the culvert outlet for all tailwater
cation purposes, the original data were reanalyzed
conditions are also shown in figures 5-8 and 5-9.
5-4
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