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Flash Flood
Published in Saeid Eslamian, Faezeh Eslamian, Flood Handbook, 2022
The allocation of a probability or a return period to such an unprecedented event within the gauged series is problematic given the uncertainty in the form of the tail of the rate of rise distribution. Assuming a generalized logistic distribution, the return period of the 1994 15-minute rate of rise is assessed as 140 years. However, if the 1994 event is excluded from the analysis the return period is several thousand years. In this case, historical information can provide useful further guidance. A search of newspaper and other records indicates the occurrence of two other flash flood events, probably of greater magnitude than that of 1994. On July 5, 1881, amongst other details it was reported that “the Wansbeck came down in a rolling flood, the wave being 3 or 4 feet deep.” It carried a young boy away. An even more severe storm occurred on September 7, 1898, when 170 mm fell in three hours. Eighteen footbridges were washed away and roads were excavated in gullies to a depth of four to five feet (British Rainfall, 1898). The Wansbeck at Morpeth rose without warning. “It came with a strong head and increased volume so rapidly that it was in a few minutes rolling over the weirheads.” With the addition of these two historical occurrences of greater magnitude, the apparently unprecedented event in 1994 becomes the Rank 3 event in approximately 160 years (the starting year of publication of the local newspaper) and a return period of ~62 years is suggested by the Gringorten plotting position formula.
The Logistic Distribution
Published in A. Ramachandra Rao, Khaled H. Hamed, Flood Frequency Analysis, 2019
A. Ramachandra Rao, Khaled H. Hamed
The logistic distribution (Section 9.1) is a special case of this distribution with k = 0, m = ε and a = α. The generalized logistic distribution is equivalent to the log-logistic distribution (Ahmad et al., 1988). The log-logistic distribution function is given by Eq. 9.2.3. (
Design flood computation at ungauged catchments of Baitarani River Basin using scaling concept and probabilistic time distribution of design rainfall
Published in International Journal of River Basin Management, 2022
Mahendra K. Bhuyan, Asutosh Dash, Joygopal Jena, Pradeep K. Bhunya, Akshay Kumar Bhuyan
Normally, four families of probability distributions i.e. Normal, Gamma, and Extreme Value, Wakeby are used in flood analysis (Rao & Hamed, 2000). For using Normal distributions, the data length should be too long and hence not used in the instant case. The Authors used generalized three-parameter distributions i.e. generalized extreme value (GEV) from extreme value family; generalized logistic distribution (GLD), generalized pareto (GP) from the Wakeby family; and Pearson III (PIII) distribution from the Gamma family of distributions considering the significance of the location, scale and shape parameters in distribution behaviour.