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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Slippage Hazard

Slippage Hazard
~nlh Velocitv
0.4 9.61
0.6 7.62
0.8 6.39
1.0 5.52
1.2 4.86
1.4 4.33
1.6 3.88
1.8 3.49
2.0 3.15
2.2 2.83
2.4 2.54
2.6 2.27
2.8 2.00
3.0 1.74
3.2 1.47
3.4 1.19
3.6 0.86
3.8 0.36

10

x - +
............\...........: ,~._--.... ...............................
x ......................AreB of
'\.
\: . InstBbility .
.--.-,...-------
"i...
x....
x
._.......~.. .----~x....---.
x"x
............................... .............................. ...I:...................m... ..........................-....
.....x....~_.
X-'x
.._~.~~ ..--l-x..x..x,x

V
e
1
o 5
c
1
t
U

o
o

2 J
Depth

4

Figure 6

Table 1

Toppling Moment
The rotalional stability (toppling moment) of the monolith depends on its weight resultant acting
Ihrough its center of mass (Figure 4). Note that this is based upon the conservative assumption that
the individual is standing upright and does not allempt to "lean into" the force of the flow.
Toppling occurs when the force of the oncoming flow exceeds the moment due to the resultant
weight of the monolith. Note that since Ff acts through the center of rotation ("0"), it has no effect
on rotational stability. Summing moments about point "0":

1:Mo = {(W - B) x OI2Thickness)} .. (P x O!2d))

Setting this equation equal to zero and solving for velocity for an appropriate range of depths under
the base conditions produces a curve very similar to the slippage hazard curve (Figure 7).

Toppling Hazard

Toppling Hazard Depth Velocitv
0.4 15.20
10 0.6 9.83
0.8 7.t4
1.0 5.52
V 1.2 4.44
e 1.4 3.66
1 1.6 3.07
0 1.8 2.60
5 2.0 2.22
C 2.2 1.91
1 2.4 1.64
t 2.6 1.4 t
Y 2.8 1.20
3.0 1.00
0 3.2 0.82
3.4 0.64
0 2 J 4 3.6 0.45
Depth 3.8 0.19
Figure 7 Table 2
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