Paleohydrology: Difference between revisions
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“There is substantial uncertainty and controversy in estimating magnitudes and frequencies of extreme floods larger than modern observations. Because of the unknown flood potential inherent in using relatively short traditional historical observations, and the potential catastrophic effects of dam failure, large-dam owners adopted the Probable Maximum Flood (PMF) concept. The PMF is the ‘flood that may be expected from the most severe combination of meteorologic and hydrologic conditions that are reasonably possible in a region’ (U.S. Army Corps of Engineers, 1994). Paleohydrologic estimates of the maximum flood in a watershed are usually far less than PMF values calculated using classical hydrologic analysis methods. Several recent paleoflood studies, primarily conducted by the U.S. Geological Survey and the Bureau of Reclamation, demonstrated large differences between the maximum paleoflood estimates and the design PMF for various watershed. Jarrett (1998) estimated the maximum flood, using paleohydrologic methods, in the past 10,000 years for Elkhead Creek is about 13% of the PMF estimate. Studies conducted by Jarrett and Costa (1988), Grimm (1993), Levish et al. (1994), and Ostenaa and Levish (1995) noted that the maximum estimated peak paleoflood flows averaged about 7% of the PMF. On the other hand, at least four floods larger than 70% of the PMF have been observed in the United States in the last 40 years (Bullard, 1986).<ref name="RD-47" /> | “There is substantial uncertainty and controversy in estimating magnitudes and frequencies of extreme floods larger than modern observations. Because of the unknown flood potential inherent in using relatively short traditional historical observations, and the potential catastrophic effects of dam failure, large-dam owners adopted the Probable Maximum Flood (PMF) concept. The PMF is the ‘flood that may be expected from the most severe combination of meteorologic and hydrologic conditions that are reasonably possible in a region’ (U.S. Army Corps of Engineers, 1994). Paleohydrologic estimates of the maximum flood in a watershed are usually far less than PMF values calculated using classical hydrologic analysis methods. Several recent paleoflood studies, primarily conducted by the U.S. Geological Survey and the Bureau of Reclamation, demonstrated large differences between the maximum paleoflood estimates and the design PMF for various watershed. Jarrett (1998) estimated the maximum flood, using paleohydrologic methods, in the past 10,000 years for Elkhead Creek is about 13% of the PMF estimate. Studies conducted by Jarrett and Costa (1988), Grimm (1993), Levish et al. (1994), and Ostenaa and Levish (1995) noted that the maximum estimated peak paleoflood flows averaged about 7% of the PMF. On the other hand, at least four floods larger than 70% of the PMF have been observed in the United States in the last 40 years (Bullard, 1986).<ref name="RD-47" /> | ||
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Revision as of 01:12, 17 September 2022
“Paleohydrology can be defined as the study of the evidence of the movement of water and sediment in stream channels before the time of hydrologic recorders, direct measurements, or historical observation. The value of paleohydrology is that it is a potential source of long-term data that can be used in the extension of historical records and the estimation of the frequency and magnitude of extreme flood events. For example, the geologic evidence of past flood events may be expressed as backwater sediment deposits in a stream tributary. The age of the deposits can be estimated using carbon-dating methods. The flow magnitude represented by the elevation of the deposits can be estimated using hydraulic modeling. This information on the age and magnitude of extreme flood events is then incorporated in flood frequency analysis. Paleohydrology is useful in estimating frequency curves, especially beyond the intermediate range of observed data i.e. 100-500 years. This additional source of information could be important to flood damage calculations, floodplain management, and dam safety evaluations.[1]
“There is substantial uncertainty and controversy in estimating magnitudes and frequencies of extreme floods larger than modern observations. Because of the unknown flood potential inherent in using relatively short traditional historical observations, and the potential catastrophic effects of dam failure, large-dam owners adopted the Probable Maximum Flood (PMF) concept. The PMF is the ‘flood that may be expected from the most severe combination of meteorologic and hydrologic conditions that are reasonably possible in a region’ (U.S. Army Corps of Engineers, 1994). Paleohydrologic estimates of the maximum flood in a watershed are usually far less than PMF values calculated using classical hydrologic analysis methods. Several recent paleoflood studies, primarily conducted by the U.S. Geological Survey and the Bureau of Reclamation, demonstrated large differences between the maximum paleoflood estimates and the design PMF for various watershed. Jarrett (1998) estimated the maximum flood, using paleohydrologic methods, in the past 10,000 years for Elkhead Creek is about 13% of the PMF estimate. Studies conducted by Jarrett and Costa (1988), Grimm (1993), Levish et al. (1994), and Ostenaa and Levish (1995) noted that the maximum estimated peak paleoflood flows averaged about 7% of the PMF. On the other hand, at least four floods larger than 70% of the PMF have been observed in the United States in the last 40 years (Bullard, 1986).[1]
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Revision ID: 3660
Revision Date: 09/17/2022