Flood Frequency Analysis of Lower Tapi River Basin: A Case Study of Surat

Flooding is a widespread, recurring, and devastating natural hazard that occurs all over the world. Estimating stream flow has a significant financial impact because it can aid in water resource management and provide protection from water scarcity and potential flood damage. The objective of the study is to carry out a flood frequency analysis of the lower Tapi River Basin, Surat, and to assess which method is more suitable for finding the return period of particular peak discharge. The lower Tapi River Basin is subjected to severe floods during monsoon times. Gumbel's distribution method, Log Pearson Type III (LP3), and Generalized Extreme value probability distribution methods were employed for simulating the future flood discharge scenarios using annual peak flow data (1980–2020), i.e., 41 years from one gauging station (Nehru Bridge) of the lower Tapi River Basin. As a result, a frequency analysis was carried out to correlate the magnitude of occurrences with their frequency of occurrence using a probability distribution. The estimated design floods for different return periods (Tr), such as 2, 10, 25, 50, 100, 150, and 200, were obtained and compared. At a 5% significance level, three goodness of fit tests were used to the fitted distributions: Chi-squared, Kolmogorov–Smirnov, and Anderson–Darling. Based on the above study, it is concluded that Gumbel’s Distribution method is more reliable for the lower Tapi Basin compared to the other two methods. Hydrologists, water resources engineers, and floodplain managers will all may benefit from the study's conclusions.