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

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Bedding for RCP pipe should be 3/8-inch minus squeegee or 3/4-inch
washed rock, six to eight inches deep under the pipe and backfilled
to the spring line.

6.3 HydraUlic Design

storm sewers shall be designed to convey initial storm peaks
without surcharging the sewer. To ensure that this objective is
achieved, the hydraulic grade line shall be calculated by
accounting for pipe friction losses and pipe form losses. Total
hydraulic losses will include friction, expansion, contraction,
bend, and junction losses. The final energy grade line shall be
at or below the proposed ground surface. The methods for
estimating the hydraulic losses are presented in the following
sections.

6.3.1

pipe Friction Losses

The Manning I s "n" values to be used in the calculation of storm
sewer capacity are presented in Table 6-1 for concrete and plastic
pipe and Table 9-1 .for corrugated metal pipe.

6.3.2

pipe Form Losses

Generally, between the inlet and outlet the flow encounters a
variety of configurations in the flow passageway such as changes in
pipe size, branches, bends, junctions, expansions, and
contractions. These shape variations impose losses in addition to
those reSUlting from pipe friction. Form losses are the result of
fully developed turbulence and can be expresses as follows:

HL = K (V2/2g) (Equation 6.1)
Where: HL = head loss (feet)
K = loss coefficient
V2 = velocity head (feet)
2g
g = gravitational acceleration (32.2 ft/sec2)

The following is a discussion of a few of the common types of form
losses encountered in sewer system design. The user is referred to
the USDCM or other professional manuals for additional discussion.

1. Expansion Losses

6-3

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