Demonstrating Floodplain Uncertainty Using Flood Probability Maps

• Published in: Journal of the American Water Resources Association Vol. 43; no. 2; pp. 359 - 371
• Main Authors: Smemoe, C.M, Nelson, E.J, Zundel, A.K, Miller, A.W
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-04-2007; American Water Resources Association
• Subjects: Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; flooding; floodplain delineation; floodplains; floods; geospatial analysis; Hydrology; Hydrology. Hydrogeology; Natural hazards: prediction, damages, etc; probability analysis; risk assessment; simulation; simulation models; statistical analysis; statistics; surface water hydrology; United States; Virgin River valley; Utah; USA; prediction maps; risk assessment; floods; models; floodplain delineation; maps; probability; simulation; geospatial analysis; flooding; technology; North America; surface water; floodplains; hydraulics; surface water hydrology; water resource management; prediction; methodology; statistics
• ISSN: 1093-474X; 1752-1688
• DOI: 10.1111/j.1752-1688.2007.00028.x

The U.S. Federal Emergency Management Agency (FEMA) flood maps depict the 100-year recurrence interval floodplain boundary as a single line. However, because of natural variability and model uncertainty, no floodplain extents can be accurately defined by a single line. This article presents a new approach to floodplain mapping that takes advantage of accepted methodologies in hydrologic and hydraulic analysis while including the effects of uncertainty. In this approach, the extents of computed floodplain boundaries are defined as a continuous map of flood probabilities, rather than as a single line. Engineers and planners can use these flood probability maps for viewing the uncertainty of a floodplain boundary at any recurrence interval. Such a flood probability map is a useful tool for visualizing the uncertainty of a floodplain boundary and represents greater honesty in engineering technologies that are used for flood mapping. While institutional barriers may prevent adoption of such definitions for use in graduated flood insurance rates (as most other insurance industries use to account for relative risks), the methods open the door technically to such a reality.