14
12
10
8
6
4
2
0
1.0
0.2
0.4
0.6
0.8
1.2
1.4
1.6
1.8
2.0
MaximumStage/Flood Stage
a. Frequency distribution.
2.0
1.6
1.2
0.8
0.4
0
99.99 99.9
99
95 90 80 70 50 30 20 10 5
1
0.1 0.01
Percentage of Time Equalled or Exceeded
b. Exceedance probability.
Figure 8. Statistics for the ice events shown in Figure 7.
confidence than for ice-related stages; therefore, it
(Fig. 10a) it is evident that the maximum ice-relat-
is helpful to develop some idea of the relation-
ed stage almost always occurs on or before the
ships between them. From Figure 9 it appears
date of the maximum discharge. This is because
that normalized stage is roughly proportional to
ice jams generally form on the rising limb of the
both maximum discharge and maximum AFDD.
hydrograph, and although a large-discharge event
However, significant scatter in the data prevents
is required to break up the ice and cause a jam, an
a clear relationship. There does not appear to be
even larger discharge will cause the jam to fail
any correlation between maximum discharge and
and wash out.
AFDD.
The relationship between the date of the maxi-
A comparison between the date of the maxi-
mum stage and the date of the maximum AFDD
mum stage and the date of the maximum dis-
is less clear (Fig. 10b). The maximum stage associ-
charge shows a stronger correlation. In this case
ated with ice events can occur either before and
18
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