Application of Geological Information to Arizona Flood Hazard Assessment

by V. R. Baker, Univ of Arizona, Tucson, United States,
K. A. Dempsey, Univ of Arizona, Tucson, United States,
L. L. Ely, Univ of Arizona, Tucson, United States,
J. E. Fuller, Univ of Arizona, Tucson, United States,
P. K. House, Univ of Arizona, Tucson, United States,
J. E. O'Connor, Univ of Arizona, Tucson, United States,
J. A. Onken, Univ of Arizona, Tucson, United States,
P. A. Pearthree, Univ of Arizona, Tucson, United States,
K. R. Vincent, Univ of Arizona, Tucson, United States,



Document Type: Proceeding Paper

Part of: Hydraulics/Hydrology of Arid Lands (H?AL)

Abstract:

Hydrological modeling procedures applied to regulatory flood-hazard zonation can be misapplied when assumptions concerning flood-hazardous processes are violated. Geomorphological mapping of the Tortolita Mountain piedmont in southern Arizona reveals extensive high-standing nonhazardous inactive, relict Pleistocene fan surfaces within zones mapped by FEMA as subject to active alluvial fan processes and 100-year flooding. Paleoflood analysis of upstream mountain canyons documents that maximum flood discharges for the past century have been about 50% lower than the regulatory (100-year) flood discharges. Geological studies are essential complements to engineering models in order to generate public confidence that regulatory requirements derive from knowledge of real rather than idealized arid-region flood-hazard processes.

Subject Headings: Floods | Geological surveys | Public health and safety | Mountains | Mapping | Geomorphology | Geology | Arizona | United States

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