Investigating Maximum Discharge of Runoff Values in Shiraz Hydro Geomorphic Basin Using Gamble Distribution Model

Among natural hazards, floods are of special importance in terms of financial and human losses. According to available statistics and information, flood damage in most parts of the world, especially in developing countries, is the the most distructive and generally makes socio-economic and environmental damages. So, efforts for reducing the damage are the duties of related agencies. Estimating and determining the maximum amount of flood is one of the first steps for reducing its damage. Therefore, providing a definition of it is a fundamental step. In this regard, the selection of the maximum possible flood plays an important role. By definition, the maximum possible flood is the largest flood that can reasonably be expected to occur in a particular region and time  (World Meteorological Organization, 1986). Frequency analysis is one of the reliable methods in flood estimation if there are sufficient statistics and it is possible to fit a suitable distribution function. This method, which uses a complete statistical series (all available data), often uses normal statistical distributions, normal logs, three-factor normal logs, limit values distribution, Pearson, Pearson logs, and WebStud program (13). The purpose of frequency analysis of events in hydrology is to obtain the maximum probability of occurrence of values. The selected area for studying the geomorphic basin of Shiraz is in the sections of Aliabad, Maroon, Eghbalabad, Chenar Sukhteh and Bagh-e-Safa stations. In this study, long-term precipitation statistics in the rain gauge station of Shiraz geomorphic basin over a period of 50 years and maximum daily discharge statistics in a period of 44 years were used.