ETL 1110-2-367
31 Mar 95
interior analysis could be performed without consideration of
physiographic origins of the interior and exterior events. Thus,
exterior conditions, thus simplifying the analysis. The
the critical focus for the analysis must be an assessment of
occurrences could be correlated and either dependent or
coincidence.
independent, but it would not affect the analysis.
e.
Inspection of the historic record is required to
c.
At the other extreme, it is possible that there is
determine correlation, independence, and coincidence.
complete coincidence, e.g., high exterior levels are always
Establishing bounds on the consequences of decisions regarding
present when an interior event occurs. The occurrences would
these factors is an important analytical approach. Analysis at
likely be correlated, although not necessarily dependent, but it
the two extremes of assuming complete coincidence and
would not be important to the analysis approach.
noncoincidence is useful. Also, by determining the relative
consequences of independence, judgments regarding its
d. The study situation most likely lies between these two
importance to the study can be made. Table 2-1 summarizes
hydrologic analysis considerations for various levels of
extremes. Analyses to determine the degree of correlation may
coincidence and dependence of interior and exterior conditions.
help determine the likelihood of coincidence or independence
but are of doubtful value. Correlation studies are most useful for
2-7.
Interior Analysis Computational Methods
developing a predictive capability. Formal study to determine
the degree of independence is not possible now. Lack of
Two hydrologic computation methods are normally performed
correlation can suggest, but not prove, independence. More
for analyses of interior areas: continuous record simulation, and
likely, the degree of dependence is based on inspection of the
hypothetical events. Analyses of significant historic events for
available record and judgments of the meteorological and
Table 2-1
Assessment of Coincidence
2-3
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