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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one for each flow path. Allowances should be made for head
loss due to the impact at junctions. The head loss for a
straight through manhole or at an inlet entering the sewer is
calculated from the original equation for form losses
(Equation 6.1). The head loss at a junction can be calculated
from:

HL = (V,'/2g) - Kj (V!'/2g)

where V, is the outfall flow velocity
velocity. The loss coefficient, Kj, for
presented in Table 6-5.

(Equation 6.5)

and! V is the inlet
various junctions is

6.3.3

storm Sewer Outlets

When the storm sewer system discharges into the Major Drainageway
system (usually an open channel), additional losses occur at the
outlet in the form of expansion losses (refer to Section 6.3.2).
For a headwall and no wingwalls, the loss coefficient Ke = 1.0
(refer to Table 6-2), and for a flared-end section the loss
coefficient is approximately 0.5 or less.

6.3.4

PartiallY Pull PiDe Plow

When a storm sewer is not flowing full, the sewer acts like an open
channel, and the hydraulic properties can be calculated using open
channel techniques (refer to Section 5). For convenience, charts
for various pipe shapes have been developed for calculating the
hydraulic properties (Figures 6-1, 6-2, and 6-3). The data
presented assumes that the friction coefficient, Manning's "n"
value, does not vary throughout the depth.

6.3.5

Hydraulic Research

The American Public Works Association (APWA) has conducted research
into the head losses at various junctions and manholes. The work
consisted of experimentally modeling three types of sewer
junctions: junctions with a 90 degree bend, junctions of a main
with a perpendicular lateral, and junctions of two opposed
laterals. The work was primarily directed at sanitary sewers
because the sizes investigated (i.e., manhole diameter to sewer
diameter ratio of 2.3 to 4.6) and the flow conditions ( i. e. ,
pressure flow) were typical for sanitary sewers. However, several
trends were observed that are considered to be suitable for storm
sewers, including specific energy loss coefficients that have been
adopted for these Criteria. The trends observed from the test
results are as follows:

6-5