Analysis and assessment of flood magnitude and frequency in the Yang River basin

Abstract

Since the magnitude and frequency of floods are necessary information for planning flood protection and mitigation, the objective of this study was then related to the analysis and assessment of the magnitude and frequency of floods in the frequently flooded downstream areas of the Yang River basin. In this study, the selection of probability distribution functions, namely, Gamma, Lognormal, Generalized Extreme Value, Gumbel, and Weibull distributions, was carried out. The method of maximum likelihood estimation was used to estimate the parameters of the probability distributions based on the annual maximum daily discharge of four selected streamflow stations for the 30-year data series (1990-2019). The goodness-of-fit tests, i.e., the Kolmogorov-Smirnov test and Akaike Information Criterion, were used to evaluate the adequacy of fitting probability distributions to the observed discharge data. The results indicated that the Weibull distribution was better suited amongst other distributions for analyzing and assessing flood magnitude and frequency. The relationships between maximum flood discharges and return periods revealed that the peak flood discharges in the Yang River at the Ban Kut Kwang station (E.70) for return periods of 10, 25, 50 and 100 years were 718.7, 801.4, 853.8, and 900.2 m³/s, respectively. Another example is that the peak flood discharges in the Yang River at Ban Tha Ngam (E.92) for return periods of 10, 25, 50 and 100 years were 713.2, 815.1, 881.0, and 940.2 m³/s, respectively. Considering peak flood discharges for the same return period at the four streamflow stations, it was found that the increase of peak flood discharges varied according to their drainage areas. Moreover, the relationships between drainage areas and peak flood discharges were also developed for estimating discharges at ungauged locations along the main river. In brief, the framework and obtained results from this study will be beneficial for effective flood mitigation and management in the Yang River basin.