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Water Science and Applications



  • Paleohydrology
  • Floods

Index Terms

  • 1821 Hydrology: Floods
  • 1824 Hydrology: Geomorphology
  • 1833 Hydrology: Hydroclimatology
  • 1854 Hydrology: Precipitation



The geology and geography of floods

Jim E. O'Connor

U.S. Geological Survey, Portland, Oregon

Gordon E. Grant

U.S. Forest Service, Corvallis, Oregon

John E. Costa

U.S. Geological Survey, Portland, Oregon

From a global perspective, the magnitude, duration, and volume of riverine floods vary widely depending on source mechanism, global location, geology, and physiography. But despite this variance, there are real physical limits as to how large a flood can be. Meteorological floods result from individual storms of various types that deliver water volumes as great as 1011 m3 over a few days or weeks as well as from seasonally persistent climate patterns that deliver upwards of 1012 m3 over several weeks or months and cause peak discharges of as much as 105 m3/s within large, continental-scale basins. The fundamental limits to meteorologic flooding depend primarily on precipitation rates and volumes, and the efficiency with which distributed rainfall concentrates into channel networks. Global and U.S. flood records show that for basins primarily affected by individual storms, the largest flows are in areas where atmospheric moisture or storm tracks are intercepted by local topographic relief. For larger basins, the largest flows result from seasonably persistent climate patterns and, on a global basis, are generally in the tropical regions where there is more precipitable moisture. Especially notable is the contribution of high-relief topography to meteorologic flooding because of its double effect of (1) lifting of atmospheric moisture, thus increasing local precipitation, and (2) promoting faster concentration of flow into channels. Floods from dam failures and terrestrial freshwater sources such as lakes and ice caps involve similar total volumes as meteorological floods, up to 1013 m3, but with much larger discharges—as great as 2·107 m3/s. The largest well-documented dam-failure floods have been during Pleistocene ice ages when glaciers and changing hydrologic conditions deranged drainage systems, causing large lakes to breach ice dams and basin divides. The largest historic floods from terrestrial water sources have had discharges as great as 1.5·106 m3/s and include floods from volcanic-induced melting of ice caps and failures of ice and landslide dams. The fundamental limits to dam-failure floods primarily arise from the size of the outlet channel and the volume of the impounded waterbody.

Citation: O'Connor, J. E., G. E. Grant, and J. E. Costa (2002), The geology and geography of floods, in Ancient Floods, Modern Hazards: Principles and Applications of Paleoflood Hydrology, Water Sci. Appl., vol. 5, edited by P. K. House et al., pp. 359–385, AGU, Washington, D. C., doi:10.1029/WS005p0359.


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