TM 5-820-4/AFM 88-5, Chap 4
APPENDIX B
HYDRAULIC DESIGN DATA FOR CULVERTS
rel slope on inlet-control flow in conventional
B-1. General.
culverts is negligible. Nomography for determin-
a. This appendix presents diagrams, charts,
ing culvert capacity for inlet control were devel-
coefficients and related information useful in de-
oped by the Division of Hydraulic Research, Bu-
sign of culverts. The information largely has been
reau of Public Roads. (See Hydraulics of Bridge
obtained from the U.S. Department of Transpor-
Wateways.) These nomography (figs B2 through
tation, Federal Highway Administration (for-
B9) give headwater-discharge relations for most
merly, Bureau of Public Roads), supplemented or
conventional culverts flowing with inlet control,
modified as appropriate by information from var-
ious other sources and as required for consistency
with design practice of the Corps of Engineers.
B-3. Outlet control.
b. Laboratory tests and field observations show
a. Culverts flowing with outlet control can flow
two major types of culvert flow: flow with inlet
with the culvert barrel full or partially full for part
control and flow with outlet control. Under inlet
of the barrel length or for all of it (fig B10). If
control, the cross-sectional area of the culvert bar-
the entire barrel is filled (both cross section and
rel, the inlet geometry and the amount of head-
length) with water, the culvert is said to be in full
water or pending at the entrance are of primary
flow or flowing full (fig B1OA and B). The other
importance. Outlet control involves the additional
two common types of outlet-control flow are shown
consideration of the elevation of the tailwater in
in figure B1OC and D. The procedure given in
the outlet channel and the slope, roughness, and
this appendix for outlet-control flow does not give
length of the culvert barrel. The type of flow or
an exact solution for a free-water-surface condi-
the location of the control is dependent on the
tion throughout the barrel length shown in figure
quantity of flow, roughness of the culvert barrel,
B-1OD. An approximate solution is given for this
type of inlet, flow pattern in the approach channel,
case when the headwater, HW, is equal to or greater
and other factors. In some instances the flow con-
than 0.75D, where D is the height of the culvert
trol changes with varying discharges, and occa-
barrel. The head, H, required to pass a given quan-
sionally the control fluctuates from inlet control
tity of water through a culvert flowing full with
to outlet control and vice versa for the same dis-
control at the outlet is made up of three major
charge. Thus, the design of culverts should con-
parts. These three parts are usually expressed in
sider both types of flow and should be based on
feet of water and include a velocity head, an en-
the more adverse flow condition anticipated.
trance loss, and a friction loss. The velocity head
B-2. Inlet control. The discharge capacity of a
(the kinetic energy of the water in the culvert
culvert is controlled at the culvert entrance by
the depth of headwater (HIV) and the entrance
geometry, including the area, slope, and type of
the type or design of the culvert inlet and is ex-
inlet edge. Types of inlet-controlled flow for un-
pressed as a coefficient& times the velocity head
submerged and submerged entrances are shown
at A and B in figure B1. A mitered entrance (fig
BlC) produces little if any improvement in effi-
entrances are given in table B1. The friction loss,
ciency over that of the straight, sharp-edged, pro-
Hf, is the energy required to overcome the rough-
jecting inlet. Both types of inlets tend to inhibit
ness of the culvert barrel and is usually expressed
the culvert from flowing full when the inlet is sub-
in terms of Manning's n and the following expres-
merged. With inlet control the roughness and length
sion:
of the culvert barrel and outlet conditions (in-
cluding depths of tailwater) are not factors in de-
termining culvert capacity. The effect of the bar-
B-1
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