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.

Inspection of the historic record is required to

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

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

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