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Water Science and Applications

 

Keywords

  • Paleohydrology
  • Floods

Index Terms

  • 1719 History of Geophysics: Hydrology
  • 1869 Hydrology: Stochastic processes
  • 1821 Hydrology: Floods
  • 1824 Hydrology: Geomorphology

Article

WATER SCIENCE AND APPLICATION, VOL. 5, PP. 295-310, 2002

Paleoflood hydrology of the Paria river, southern Utah and northern Arizona, USA

R. H. Webb

U.S. Geological Survey, Tucson, Arizona


J. B. Blainey

California State University Foundation, U.S. Geological Survey, Sacramento, California


D. W. Hyndman

Department of Geological Sciences, Michigan State University, Lansing, Michigan


Three critical assumptions in paleoflood studies are that (1) successively higher-stage floods leave depositional evidence in flood deposits, (2) that the height of the flood deposit can be used as evidence of the water-surface elevation, and (3) one-dimensional flow models accurately depict water movement in bedrock-constrained channels. Slackwater deposit/paleostage indicator (SWD/PSI) evidence preserved along the Paria River in southern Utah and northern Arizona can be used to challenge or verify these assumptions as well as improve flood-frequency estimates. The Paria River is a highly sediment-charged river that occasionally produces exceptionally large floods. Downstream from the Utah-Arizona border, the river flows through a narrow bedrock canyon in Navajo Sandstone where considerable SWD/PSI evidence is preserved under overhanging walls, particularly at one site, informally named Bonza Alcove. The paleoflood record, which begins at 4.2 ka with a massive clay, consists of 5 flood units with an inset deposit of an additional 6 flood units. The stratigraphy demonstrates that smaller-discharge floods may overtop the units of larger floods owing to the nature of flood deposition in three dimensions. Silt lines correlative with some of the flood deposits were preserved across the flood deposits and on the sandstone walls; these silt lines were 0.30 to 0.90 m above the corresponding flood deposit. Using one-dimensional step-backwater analysis, the discharge that best matches the silt-line evidence for the largest historical flood is 1,200 m3s, which is 2.6 times larger than the largest flood in the gaging record (1923–1998). Four different scenarios of varying amounts of paleoflood information are used in flood-frequency analysis, and the effect of the addition of paleoflood data in estimating flood recurrence quantiles is assessed.

Citation: Webb, R. H., J. B. Blainey, and D. W. Hyndman (2002), Paleoflood hydrology of the Paria river, southern Utah and northern Arizona, USA, in Ancient Floods, Modern Hazards: Principles and Applications of Paleoflood Hydrology, Water Sci. Appl., vol. 5, edited by P. K. House et al., pp. 295–310, AGU, Washington, D. C., doi:10.1029/WS005p0295.

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