0.011-0.014

0.016-0.018

36-96 inches

0.019-0.024

0.017-0.021

control equals the discharge with inlet control. For

culverts with free flow and control at the outlet,

length scale to barrel area and mark point

on turning line.

values is permitted in the range of headwater depths

(3) Pivot the straight edge on this point on

equal to or less than twice the barrel height. The

t h e turning line and connect given dis-

upper limit of this range of headwater depths is

charge rate. Read head in feet on the head

designated by a horizontal dotted line on the charts.

scale.

do not impose any limitation; merely read the solid-

B-43, prepared by the Bureau of Public Roads,

line curves. The symbol AHW means allowable

headwater depth. The charts permit rapid selection

present headwater discharge relations convenient

of a culvert size to meet a given headwater limitation

for use in design of culverts of the most common

for various entrance conditions and types and shapes

types and sizes. The solid-line curve for each type

of pipe. One can enter with a given discharge and

and size represents for a given length: slope ratio

read vertically upward to the pipe size that will carry

the culvert capacity with control at the inlet; these

the flow to satisfy the headwater limitation of the

curves are based generally on model data. For those

design criteria. The major restriction on the use of

culvert types for which a dashed-line curve is shown

the charts is that free flow must exist at the outlet.

in addition to a solid-line curve, the dashed line

In most culvert installations free flow exists, i.e.,

represents for a given length: slope ratio the dis-

flow passes through critical depth near the culvert

charge capacity for free flow and control at the out-

outlet. For submerged flow conditions the solution

let; these curves are based on experimental data and

can be obtained by use of the outlet control nomo-

backwater computations. The length: slope ratio is

graphs.

case is the value at which the discharge with outlet

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