FLOOD00281

• County: Larimer
• Community: Greeley
• Title: Design Criteria and Construction Specifications volume 2 of 5 Storm Drainage Criteria
• Date: 10/1/1997
• Prepared For: Greeley
• Prepared By: Department of Public Works
• Floodplain - Doc Type: Educational/Technical/Reference Information

6.9 Design Example

The following calculation example, including the calculation Table
6-6, and Figures 6-4 a.nd 6-5, were obtained from Modern Sewer
Desian, AISI, Washington D.C., 1980 and edited foJr the calculation
of manhole and junction losses in accordance '.ri'th this section.

Given:

(a) Plan and Profile of storm sewer (Figures 6-4
and 6-5); example calculation form (Table 6-
6) .
(b) station 0+00 (outfall) data as follows:

Design Discharge Q = 145 cfs (Column 9)
Invert of PipE;! = 94.50 fee't (Column 2)
Diameter D = 66-inl:h RCP (Column 3)
Starting 'Water Surface W.S. = 100 f'~et (Column 4)
Area of Pipe A = 23.76 sq. ft. (Column 6)
Velocity = Q/A V = 6.1 fps (Column 8)
Pipe RoughnesB n = 0.013
Notes:

(I) Numbers :..n brackets refers to th'3 Columns on Table
6-6

(ii) Sizes of the storm sewer were dlet'3rmined during the
preliminary design phases.

Find:

Hydraulic Grade Line and Energy Grade Line for
storm se~ler.

Discussion: The following procedure is b.ased on full-flow
pipe conditions. If thl~ piPl3 is flowing
substantially full (i.e., greater than 80
percent), the following procedures can be used
with minimal loss of accuracy. However, the
design.er is responsible for checking the
assump'l:ions (Le., check for full flow) to assure
that tl:le calculations are correct.

STEP 1:

The normal depth is greater than critical depth, dn
> de; the:refore, calculations 1;0 begin at outfall,
working upstream. CompU1te the fOllowing
parameters:

<l> = 2qn2 =
2.21

2 x 32.2 x (. 01:u.:,
2.21

This equation is
equation by solving
velocity head.

der i ved from the Manning's
for veloci1ty and converting to

6-8

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