Uncertainty in Flood Estimates Associated with Roughness Coefficient
Publication: Journal of Hydraulic Engineering
Volume 124, Issue 2
Abstract
Although paleoflood reconstructions are frequently used to provide discharge estimates of extreme floods, a concern remains regarding uncertainty in Manning's n-values. An analysis of this uncertainty relative to a commonly used step-backwater model was performed for channel reaches in five canyon rivers. Values of n were selected for each study reach using four methods. Each set of n-values was then varied by ±10% and ±25%. The percentage change in discharge associated with varying n-values is inversely proportional to channel gradient and to width/depth ratio, and proportional to roughness. For channels with a gradient less than or equal to approximately 0.01, varying n by ±25% produces a maximum change of 20% in discharge. The greatest discrepancy among n-values estimated using the four methods occurred for channels with relatively low gradient and low roughness, but associated discharge varied fairly consistently between 13 and 27%. These results indicate that uncertainties in discharge estimation resulting from the roughness coefficient in step-backwater modeling of paleofloods are comparable to or lower than uncertainties associated with other methods of indirectly estimating flood discharges.
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References
1.
Arcement, G. J., Jr., and Schneider, V. R. (1989). “Guide for selecting Manning's roughness coefficients for natural channels and flood plains.”U.S. Geological Survey Water-Supply Paper 2339, Federal Center, Colo.
2.
Baker, V. R.(1987). “Paleoflood hydrology and extraordinary flood events.”J. Hydrol., Amsterdam, The Netherlands, 96, 79–99.
3.
Baker, V. R. (1988). “Palaeoflood hydrology of tropical rivers.”Int. Seminar on Hydrol. of Extremes, Roorkee, India, 1–10.
4.
Baker, V. R. (1989). “Magnitude and frequency of paleofloods.”Floods: hydrological, sedimentological and geomorphological implications, K. Beven and P. Carlings, eds., John Wiley & Sons, Inc., London, U.K., 171–183.
5.
Barnes, H. H., Jr. (1967). “Roughness characteristics of natural channels.”U.S. Geological Survey Water-Supply Paper 1849, Federal Center, Colo.
6.
Benson, M. A. (1962). “Factors influencing the occurrence of floods in a humid region of diverse terrain.”U.S. Geological Survey Water-Supply Paper 1580-B, Federal Center, Colo.
7.
Benson, M. A. (1964). “Factors affecting the occurrence of floods in the Southwest.”U.S. Geological Survey Water-Supply Paper 1580-D, Federal Center, Colo.
8.
Burnham, M. W., and Davis, D. W.(1990). “Effects of data errors on computed steady-flow profiles.”J. Hydr. Engrg., ASCE, 116, 914–929.
9.
Chow, V. T. (1959). Open-channel hydraulics. McGraw-Hill Book Co., Inc., New York, N.Y.
10.
Cowan, W. L.(1956). “Estimating hydraulic roughness coefficients.”Agric. Engrg., 37, 473–475.
11.
Dawdy, D. R., and Motayed, A. K. (1979). “Uncertainties in determination of flood profiles.”Inputs for risk analysis in water systems, E. A. McBean, K. W. Hipel, and T. E. Unny, eds., Water Resources Publications, Ft. Collins, Colo., 193–208.
12.
Ely, L. L., Enzel, Y., Baker, V. R., and Cayan, D. R.(1993). “A 5000-year record of extreme floods and climate change in the southwestern United States.”Sci., 262, 410–412.
13.
Enzel, Y., Ely, L. L., House, P. K., and Baker, V. R.(1993). “Paleoflood evidence for a natural upper bound to flood magnitudes in the Colorado River Basin.”Water Resour. Res., 29, 2287–2297.
14.
Enzel, Y., Ely, L. L., Martinez-Goytre, J., and Vivian, R. G.(1994). “Paleofloods and a dam-failure flood on the Virgin River, Utah and Arizona.”J. Hydrol., Amsterdam, The Netherlands, 153, 291–315.
15.
HEC-2 water surface profiles: program user's manual. (1990). U.S. Army Corps of Engineers, Hydrologic Engrg. Ctr., Davis, Calif.
16.
Jarrett, R. D.(1984). “Hydraulics of high-gradient streams.”J. Hydr. Engrg., ASCE, 110, 1519–1539.
17.
Jarrett, R. D.(1987). “Errors in slope-area computations of peak discharges in mountain streams.”J. Hydrol., Amsterdam, The Netherlands, 96, 53–57.
18.
Jarrett, R. D., and Malde, H. E.(1987). “Paleodischarge of the late Pleistocene Bonneville Flood, Snake River, Idaho, computed from new evidence.”Geological Soc. of Am. Bull., 99, 127–134.
19.
Limerinos, J. T. (1970). “Determination of the Manning coefficient from measured bed roughness in natural channels.”U.S. Geological Survey Water-Supply Paper 1898-B, Federal Center, Colo.
20.
O'Connor, J. E., and Webb, R. H. (1988). “Hydraulic modeling for paleoflood analysis.”Flood geomorphology, V. R. Baker, R. C. Kochel, and P. C. Patton, eds., John Wiley & Sons, Inc., New York, N.Y., 393–402.
21.
Partridge, J. B., and Baker, V. R.(1987). “Palaeoflood hydrology of the Salt River, Arizona.”Earth Surface Processes and Landforms, 12, 109–125.
22.
Pickup, G. (1989). “Palaeoflood hydrology and estimation of the magnitude, frequency and areal extent of extreme floods—an Australian perspective.”Civ. Engrg. Trans., Canberra, Australia, CE34, 19–29.
23.
Salas, J. D., Wohl, E. E., and Jarrett, R. D. (1994). “Determination of flood characteristics using systematic, historical and paleoflood data.”Coping with floods, G. Rossi, N. Harmancioglu, and V. Yevjevich, eds., Kluwer, Dordrecht, The Netherlands, 111–134.
24.
Sauer, V. B., Curtis, R. E., Santiago-Rivera, L., and Gonzalez, R. (1985). “Quantifying food discharges in mountainous tropical streams.”Int. Symp. on Tropical Hydrol. and 2nd Caribbean Islands Water Resour. Congr., F. Quinones and A. V. Sanchez, eds., American Water Resources Association, Bethesda, Md., 104–108.
25.
Wohl, E. E.(1995). “Estimating flood magnitude in ungaged mountain channels, Nepal.”Mountain Res. and Devel., 15, 69–76.
26.
Wohl, E. E., Fuertsch, S. J., and Baker, V. R.(1994a). “Sedimentary records of late Holocene floods along the Fitzroy and Margaret Rivers, Western Australia.”Australian J. Earth Sci., 41, 273–280.
27.
Wohl, E. E., Greenbaum, N., Schick, A. P., and Baker, V. R.(1994b). “Controls on bedrock channel incision along Nahal Paran, Israel.”Earth Surface Processes and Landforms, 19, 1–13.
28.
Wohl, E. E., Webb, R. H., Baker, V. R., and Pickup, G. (1994c). “Sedimentary flood records in the bedrock canyons of rivers in the monsoonal region of Australia.”Colo. State Univ. Water Resour. Paper 107, Colorado State University, Ft. Collins, Colo.
Information & Authors
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Published In
Journal of Hydraulic Engineering
Volume 124 • Issue 2 • February 1998
Pages: 219 - 223
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Copyright © 1998 American Society of Civil Engineers.
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Published online: Feb 1, 1998
Published in print: Feb 1998
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