FLOOD08704

• County: Statewide
• Basin: Statewide
• Title: Hydraulics of Bridge Waterways
• Date: 3/1/1978
• Prepared For: US
• Prepared By: USDOT
• Floodplain - Doc Type: Educational/Technical/Reference Information

Oc ~ I ( Ot, ~ 1< Q.
I I
I I I
I II II II Ill-. f /1 II II II I II I I I II I II

"I.n
- r---....
....... '-.....
'-0.95 ""
- i-- "
r----.. ........ '\.
,'0,90 ~ \
"O,~5 - - "" l\
r-
1 ........... ~
..0.80 -0

" II " II , '
e = (1- ~: )

e =(1-~)
Oc

0,20

0,16

0,12

..
:.c
<3

0,08

0.04

o
0,2

0,3

0.4

0.5

"-J111'"'IIIIII"11

where Oc < 0. or

where 0. < Oc

0,6

1.0

0,7

0,8

0,9

Figure 8.-Incremental backwater coefficient for eccentricity.

M

piers with the direction of flood flow, The ratio of
the water area occupied by piers, A., to the gross
water area of the constriction, .1." both based on
the normal water surface, has been assigned the
letter J. In computing the gross water area, A." the
presence of piers in the constriction is ignored. The
incremental backwater coefficient for the more
common types of piers and pile bents can be ob-
tained from figure 7, By entering chart A with the
proper value of J and reading upward to the proper
pier type, !!.K is read from the ordinate. Obtain the
correction factor, cr, from chart B for opening ratios

other than unity. The incremental backwater co-
efficient is then:

!!.Kp = cr!!.K

The incremental backwater coefficient8 for pile
bents can, for all practical purposes, be considered
independent of diameter, width, or spacing of piles
but should be increBred if there are more than 5
piles in a bent. A bent with 10 piles should be given
a value of !!.Kp about 20 percent higher than that
shown for bents with 5 piles, If there is a possibility
of trash collecting on the piers, or piles, it is ad-

16