Q = 0.39 (JD)1.96
tion of data for ice events at North Bend, the fol-
(4)
lowing criteria were then chosen to characterize
where Q is the average daily discharge corre-
these ice events: AFDD>400 and Q >6000 cfs or
Q = 0.39 (JD)1.96, whichever is larger. Once these
sponding to ice events in cfs and JD is the Julian
Day (day 1 is 1 October of a given water year).
criteria had been arrived at, they were applied to
This relationship, shown in Figure 13, describes
the data for 19501990 to evaluate the effective-
the minimum average daily discharge required
ness of this classification system. The first date
for an ice event to occur on a given date. From
that met the criteria in a given year was selected
Figure 13 we can see that the relationship reason-
as an ice event.
ably describes the minimum discharge conditions
Table 14 presents the results of application of
associated with ice events at North Bend, at least
the criteria to the historic data. The second col-
while the AFDD criterion is met. After examina-
umn identifies water years in which there was a
Table 14. Results of applying AFDD and discharge criteria to historic data at
North Bend.
Predicted
Recorded
ice event
one week of
Water
maximum
False
Negative
False negative
year
ice stage
maximum ice stage
prediction
prediction
prediction
√
√
1950
√
√
1951
√
√
1952
√
√
1953
√
1954
√
√
1955
√
1956
√
1957
√
√
1958
√
√
1959
√
√
1960
√
√
1961
√
√
1963
√
1964
√
1965
√
1966
√
1967
√
1968
√
1969
√
√
1970
√
√
1971
√
√
1972
√
√
1973
√
√
1974
√
1975
√
√
1976
√
√
1977
√
√
1978
√
√
1979
√
√
1980
√
1981
√
√
1982
√
√
1983
√
1984
√
√
1985
√
√
1986
√
1987
√
√
1988
√
√
1989
√
1990
Note: Water year 1962 was omitted due to significant amounts of missing meteorological
data.
27
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