(1) Locate appropriate nomograph for type of

culvert selected.

(2) Begin nomograph solution by locating

starting point on length scale. To locate

the proper starting point on the length

scale, follow instructions below:

sponds to that of the culvert being used,

on the appropriate nomograph locate

starting point on length curve for the

for the culvert selected differs from that

of the nomograph, see (c) below.

intermediate between the scales given,

connect the given length on adjacent

scales by a straight line and select a point

on this line spaced between the two chart

ficient nl than that of the chart n, use

the length scales shown with an ad-

justed length Ll, calculated by the for-

mula:

(See subpara b below for n values.)

(3) Using a straight edge, connect point on

length scale to size of culvert barrel and

(1) above to given discharge and read di-

mark the point of crossing on the "turning

ameter, height, or size of culvert required.

line." See instruction c below for size con-

siderations for rectangular box culvert.

(4) Pivot the straight edge on this point on

(1)

the turning line and-connect given dis-

charge rate. Read head in feet on the head

scale. For values beyond the limit of the

chart scales, find H by solving equation

(2)

given in nomograph or by H = KQ2 where

K is found by substituting values of H and

Q from chart.

culvert selected.

(3)

for full flow for other than square boxes:

(1) Compute cross-sectional area of the rec-

tangular box.

to solve for head when culverts flow full with out-

for barrel cross sections with span B twice the

height D; its close correspondence with area

let control. They are also used in approximating

of square boxes assures it may be used for all

the head for some partially full flow conditions

sections intermediate between square and B

with outlet control. These nomography do not give

= 2D or B = 2/3D. For other box proportions

a complete solution for finding headwater. (See

use equation shown in nomograph for more

para B4.)

accurate results.

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