Flood frequency analysis supported by the largest historical flood

摘要

The use of non-systematic flood data for statistical purposes depends on the reliability of the assessment of both flood magnitudes and their return period. The earliest known extreme flood year is usually the beginning of the historical record. Even if one properly assesses the magnitudes of historic floods, the problem of their return periods remains unsolved. The matter at hand is that only the largest flood (XM) is known during whole historical period and its occurrence marks the beginning of the historical period and defines its length (L). It is common practice to use the earliest known flood year as the beginning of the record. It means that the L value selected is an empirical estimate of the lower bound on the effective historical lengthM. The estimation of the return period of XM based on its occurrence (L), i.e. M = L, gives a severe upward bias. The problem arises that to estimate the time period (M) representative of the largest observed flood XM.