From the background section of the document: "There is a need for updated guidelines for evaluating the hydrologic safety of dams, and in particular, for determining the appropriate Inflow Design Flood (IDF) and freeboard requirements. The existing hydrologic guidelines of some states and federal agencies were written in the late 1970s. Since that time, significant technological and analytical advances have been made along with better watershed and rainfall information that improve the analysis of extreme floods and quantification of incremental dam failure consequences. Many existing dams that were constructed before dam safety rules existed still do not meet regulatory guidelines for safely passing the IDF. Existing guidelines often do not treat new and existing dams the same in recognition of the fact that upgrading older dams to pass the IDF can be difficult and expensive. […] The overriding purpose of this report is to document the available data and to present the state of the practice for evaluating the hydrologic safety of dams, including inventorying current practices used by state and federal agencies. This work included a review of hydrologic guidelines currently used in each state and federal agency that regulates dams, and was guided by an independent steering committee and reviewed by the Research Work Group. A subsequent publication will include new federal guidelines for the evaluation of the hydrologic safety of dams that could be applied nationwide."