Collection System ComponentsAdvanced 28 min read

Collection System Components: Advanced Collection System Design I — Hydraulic Design & Capacity Planning

Full hydraulic sewer design using Manning's equation, minimum/maximum velocity criteria, and quantitative system capacity and buildout analysis for Colorado Collection Class 4 operators.

At the Class 4 level, slope and velocity aren't just concepts to recognize — you need to be able to design and verify them using the same equation the standards themselves are built on: Manning's equation.

Full Hydraulic Design: Manning's Equation

In U.S. customary units, for a pipe flowing full:

V = \frac{1.49}{n} R^{2/3} S^{1/2}

Where:

$V$ = mean velocity (ft/s)
$n$ = Manning's roughness coefficient (dimensionless — a property of the pipe's interior surface)
$R$ = hydraulic radius (ft) = cross-sectional flow area ÷ wetted perimeter
$S$ = slope of the pipe (ft/ft, i.e., the "grade" expressed as a decimal)

For a circular pipe flowing completely full, the hydraulic radius simplifies to

R = D/4

, where

D

is the pipe diameter in feet (since area =

\pi D^2/4

and wetted perimeter =

\pi D

when full).

Regulatory design practice — including the Ten States Standards —

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