FLOOD08875

• County: Boulder
• Basin: South Platte
• Title: Analysis of a High Hazard Flood Zone
• Date: 10/1/1987
• Prepared For: Boulder
• Prepared By: David Love & Associates
• Floodplain - Doc Type: Floodplain Report/Masterplan

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(fable 4). (When referring to the
hazard curve, the scale on the
vertical axis represents velocity,
while the same scale represents
the product number when
referring to the product number
curve. )

When these plots are
superimposed with respect to the
hazard envelope (Figure 11), a
"controlling product number"
curve is generated for a given
configuration of weight,
geometry, and coefficients. It is
this "controlling product
number" curve which is used to
compare different configurations
in the remainder of this analysis.

Controlling
Product Number

10

..__.. .:0:_ 511ppoge PN

..- Toppllng PN

:0: :0: .0- Controlling PN
...........-.~~;oc~:::tr.'.!=.".=l~.?;.~:r:....x;;.;:x::.I...............................

~ 5 .-ol!.' o..o..Q..().;;;o.. -:J :0:':0:,_

t ~o~ :0:,_
~~-

m.m....m................. ........................._..... ..........m................... ..................~.....

P
r
o
d

.,

o
o

3

4

2
Depth

Figure 11

Figure II is a composite of product numbers for slippage and toppling hazards. At lower depths,
the product number is controlled by slippage while at greater depths the product number is
controlled by toppling up to a limited depth where buoyancy controls. The peak represents the
intersection of the product number curves for slippage and toppling.

Sensitivity Analysis
As part of this analysis, the validity of the assumptions slated above were explored by studying the
effects of various parameters on the curves shown earlier.

As stated previ-
ously, the coeffi-
cient of drag (Cd)
is based upon
losses due to fric-
tion with the
ground surface
and momentum
changes due to
variations in flow,
and is a function
of velocity and
flow regime (Ref-
erence 5). While
the "Colorado
Floodproofing
4 Manual" states
that a minimum of
1.25 should be
Figure 12 used for rectan-
gular objects, the relatively small size of the objects under consideration led to the use of a value of
1.0 as a base coefficient. This value was varied from 1.0 to 1.5 to test the sensitivity of the param-
eter (Figure 12), and a median value of 1.25 was ultimately chosen for purposes of comparing the
effects of body geometry.

Product Number as a Function of
Coefficient of Drag

- Bose PN
- .. ..
.... Cd=l .25
...._........................m.......... .......................................... ..........................................
- Cd= 1.5
./. .' ...............-
.... -
~~.,-1.- ~."
~ ...~
.........
..~~....
~ "~
..-........................._........ ........................................... ...........................-.~.. ..~;::O:,......................
~
....

10

P

r
o
d
u 5
c
t

.,

o
o

2
Depth

3

- 11-