Comparative Study of Distribution Models for Flood Flow in Lokoja Hydrologic Station

Abstract

This study aimed to select the appropriate
probability distribution function to fit the
historical time series of the hydrologic station
at Lokoja in Nigeria's Niger/Benue River
Basin. The provision of a trustworthy
approximation of flood features using
historical time series data for the designated
stations was one of the main goals of this
effort. The National Inland Waterways
Authority (NIWA) in Lokoja provided the
flood data. Utilizing the annual maximum
series, the concept of flood frequency analysis
(FFA) was used to analyze the extreme data
(AMS). Four (4) probability distribution
models were used to suit the observed data:
Normal (N2), Gumbel (EV1), Exponential,
and Generalized extreme value (GEV). The
FFA was simulated and modelled for both
stations using the MATLAB application. On
FFA, several academic studies were
examined. To check that the time series
achieved stationary, randomness and that the
random samples were independently and
identically distributed, hydrologic data
screening was done using numerous statistical
tests at the 5% level of significance. The Pre-
Whitening Analysis process was used to
remove the time series record's visible trend
and auto-correlation. For estimating
statistical parameters, the method of
moments (MoM) was employed. The
simulated data were subjected to the chisquare
( ) and Kolmogorov-Smirnov (K-S)
goodness of fit tests at the 5% level of
significance to identify the best-fit
distribution among the four (4) frequency
distributions. The generalized extreme value
(GEV) distribution was found to be the best
approximation of flood characteristics for the
Lokoja hydrologic station in the Niger/Benue
river basin based on the results. The Lokoja
station's Kolmogorov-Smirnov (K-S) and chisquare
( ) test statistics are 0.8707 and
1.2044, respectively. These results
demonstrate that the GEV is the best
distribution for the Lokoja hydrologic station.