This paper presents an expert system to help select the best method to estimate design flood flows for civil engineering works based upon the procedures available, the nature and characteristics of the basin and existing hydrological records. The system presents the user with a list of possible methods ranked in descending grade order and optionally presents explanations which support the selected choices. Ordering is achieved using the knowledge base provided by the expert. The system recommends procedures for both preliminary estimates and final designs. The system also constitutes a valuable aid for junior engineers and experienced hydrologists in the selection of methods. Its conceptual structure can be easily generalized to treat other problems of a similar nature in the field of hydrology and water resources.