Hydraulic Design of Highway Culverts - DOT On-Line Publications

Figure A-1--Dimensionless Performance Curve for Structural Plate Elliptical Conduit,
Long Axis Horizontal, Thin Wall Projecting Entrance
The results of the above calculations are plotted in Figure A-1. A transition line is drawn
between the unsubmerged and the submerged curves. The scales are dimensionless in Figure
A-1, but the figures could be used to develop dimensional curves for any selected size of
elliptical conduit by multiplying: Q/AD 0.5 by AD 0.5 HWi /D by D.
Similar calculations were used to develop the dimensionless inlet control design curves for the
long span arches and elliptical pipe in Chapter III.
To derive overall inlet control equations for use on a computer, it is necessary to plot the
unsubmerged and submerged curves from these equations and draw the connecting transition
line. Then, the coordinates of selected points can be read from the curve and a best fit
statistical analysis performed. A polynomical curve of the following form has been found to
provide an adequate fit.
HW
D
i
⎡ Q
= A + B ⎢ 1
⎣BD
. 5
⎤ ⎡ Q
⎥ + C ⎢ 1
⎦ ⎣BD
. 5
⎤
⎥
⎦
2
⎡ Q
+ ... + X⎢
1
⎣BD
. 5
197
⎤
⎥
⎦
n
−
0.
5 S
The flow factor could be based on AD 0.5 rather than BD. 1.5 The constants for the best fit
equations are found in the user's manuals for various computer programs (20, 53, 54, 55, 59).
C. Development of Dimensionless Inlet Control Design Charts.
The dimensionless inlet control design charts provided for long span arches, circular and
elliptical pipes were derived using the equations presented in Table 8, selected constants from