watch the water !
12/11/21
The Rational Method is based on the
direct relationship between rainfall and runoff. It is expressed by the equation Q = CIA,
in which:
Q=the runoff in cu. f.p.s. from a gi,·en
area;
C=a runoff coefficient depending upon
the character of the drainage area;
I=the intensity of rainfall in inches per
hour;
A= the drainage area in acres.
Several formulas are used by engineers
to determine the flow characteristics in pipes.
Many of them girn practically the same results, but the Manning formula is the most
widely used and is recommended for use and is
as follows:
Q = A 1.486 R2/3 5112
n
in which:
Q =discharge in cubic feet per second
A= cross-sectional area of flow in square
feet
R=hydraulic radius in ft.=area of section
wetted perimeter
S=slope of pipe im·ert in ft. per foot
n=coefficient of roughness of pipe