Flood Frequency Analysis in the United States: Time to Update

A large portion of the U.S. population, infrastructure, and industry is located in flood-prone areas. As a result, floods cause an average of nearly 140 deaths and cost roughly $6 billion annually excluding flooding caused by Hurricane Katrina, which cost $200 billion alone www.usgs.gov/hazards/floods/; USGS 2006 . The 1993 Midwest flooding along the Mississippi and Missouri Rivers caused $20 billion in damages. Furthermore, these estimates neglect the real costs associated with loss of personal possessions and shattered lives and communities. With Hurricane Katrina August 2005 and recent floods in the Northeast June 2006 , Ohio winter 2007 , Texas–Oklahoma June 2007 , and central England July 2007 , it seems like damaging floods have been in the news daily over the last few years. While engineers cannot stop floods from occurring, they should seek structural and nonstructural strategies to reduce the risk of large economic losses, social vulnerability, environmental damage, and loss of life IFMRC 1994 . Development of economically efficient and rational plans requires good estimates of the risk of flooding. In the United States, that computation is done following guidelines in Bulletin 17, for which the latest update, Bulletin 17B, was published in 1982 IACWD 1982 . That update includes the skew map published 30 years ago in the original Bulletin 17 WRC 1976 , and a list of areas needing additional research. Bulletin 17B has served the nation for over 30 years; it is a remarkable document that has withstood the test of time and use. However, given long-standing problems listed in the document, recent advances that address those problems, and the current national interest in flood risk, the time has arrived to update Bulletin 17B to maintain the statistical credibility of the guidelines and to provide accurate risk and uncertainty assessments.