Hydrology and dams are two fields that are obviously closely related. So far four Bulletins have been published by the Committee: Bulletin 82. Selection of Design Flood - Current Methods (1992) Bulletin 125. Dams and Floods - Guidelines and Case Histories (2003) Bulletin 131. Role of Dams in Flood Mitigation - A Review (2006), and Bulletin 156. Integrated Flood Management (2014) These Bulletins essentially addressed floods, the risks they represent and their impact on the populations involved. Examples were given of the observed beneficial role of dams, as well as of the conceptual approaches for evaluating extreme situations. The experiences gained through the integration of flood management in the reservoir operation were described as well, along with other considerations related to climate change and real case experiences.

The present Bulletin 170 deviates slightly from this path, adopting a somewhat more technical perspective. The text consists of three chapters, conceived to be accessible to the practitioners. The first one is a useful vade mecum of usually applied "classical" hydrological methods, highlighting their key features. The second chapter describes a promising original approach to cope with the uncertainties of extreme floods. The last one focuses on the various criteria applied throughout the world to decide which level of flood severity must be considered as a reference for designing a flood evacuation system.