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

Expansion in al storm sewer conduit will rl!suI1: in a shearing
action between tile incoming high velocity jet and the
surrounding sewer boundary. As a result.. much of the kinetic
energy is dissipa1::ed by eddy currents and turbulence. The
loss of head c:an be expressed as:

HL= Ke (V//2g) [ 1 - AdA, ],

(Equation 6.2)

in which A is the cross section area, V i.s the average flow
velocity, and Ke is the loss coefficient. Subscripts 1 and 2
denote the upstream and downstream sections, respecti vely.
The value of K" is l:lbout 1.0 for a sudden expansion, and about
0.2 for a well d.,~signed expansion trclne:iticm. Table 6-2
presents the expansion loss coefficients for various flow
conditions.

2 .

Contraction Losses

The form loss due to contraction is:

HL=Kc (V//2g) [1- (A,)2/A:]'

(Equation 6.3)

where Kc is the contraction coeff icient, ~ is equal to 0.5
for a sudden contraction and about 0.1 for Cl well designed
transition. Subscripts 1 and 2 denote thl~ upstream and
downstream sections, respectively. Table 6-2 presents the
contraction loss coefficients for various flo'... conditions.

3.

Bend Losses

The head losses flJr bends, in excess of that caused by an
equivalent length of straight pipe, may be expressed by the
relation:

HL = Kb (V'/2g)

(Equation 6.4)

in which K" is the bend coefficient. The bend I::oefficient has
been found to be a function of: (a) th,~ rati,) of the radius
of curvature of tile bend to the width of the conduit, (b)
deflection angle .of the conduit, ~ gE!Ometry of the cross
section of flow, and (d) the Reynolds Number and relative
roughness. A tabulation of the recommended bend loss
coefficients for st:andard bends, radius pipe, a.nd bend through
manholes is presented in Tables 6-3 and 6.-4.

4.

Junction and Manhole Losses

more branc:h sewe,rs enter a main
The hydrllulic design of a
of two o:r more transitions,

A junction occurs \/here one or
sewer, usually at. manholes.
junction is in effect the design

6-4

I
I
I
I
I
I
I
I
I
I
I
I
II
I
I
I
I
I
I
I