Peak Flow Rate Estimates Using the GRADEX method

This book is dedicated to the GRADEX method (Gradient des valeurs extrêmes), developed in the late 1960s by the Électricité De France research group (Guillot and Duband, 1967). It is a semi-empirical hydrological method, widely used around the world for estimating peak flows of rare to very rare floods (return periods greater than a hundred years), especially when a long series of annual maximum daily rainfall and a shorter series of flow rates (typically around ten years) are available. The book begins by presenting the theoretical concepts, hypotheses, and application constraints of the method. It then offers ten complete application exercises, worked out step-by-step by strictly following the classic approach: (i) fitting the Gumbel distribution to annual maximum daily rainfall, (ii) fitting the Gumbel distribution to annual maximum daily mean flow rates after conversion into runoff depth, (iii) GRADEX extrapolation beyond the decennial pivot point, and (iv) calculating peak flow rates via an average peak coefficient.