Regional interdisciplinary paleoflood approach to assess extreme flood potential

In the past decade, there has been a growing interest of dam safety officials to incorporate a risk-based analysis for design-flood hydrology. Extreme or rare floods, with probabilities in the range of about 10−3 to 10−7 chance of occurrence per year, are of continuing interest to the hydrologic and engineering communities for purposes of planning and design of structures such as dams [National Research Council, 1988]. The National Research Council stresses that as much information as possible about floods needs to be used for evaluation of the risk and consequences of any decision. A regional interdisciplinary paleoflood approach was developed to assist dam safety officials and floodplain managers in their assessments of the risk of large floods. The interdisciplinary components included documenting maximum paleofloods and a regional analyses of contemporary extreme rainfall and flood data to complement a site-specific probable maximum precipitation study [Tomlinson and Solak, 1997]. The cost-effective approach, which can be used in many other hydrometeorologic settings, was applied to Elkhead Reservoir in Elkhead Creek (531 km2) in northwestern Colorado; the regional study area was 10,900 km2. Paleoflood data using bouldery flood deposits and noninundation surfaces for 88 streams were used to document maximum flood discharges that have occurred during the Holocene. Several relative dating methods were used to determine the age of paleoflood deposits and noninundation surfaces. No evidence of substantial flooding was found in the study area. The maximum paleoflood of 135 m3 s−1 for Elkhead Creek is about 13% of the site-specific probable maximum flood of 1020 m3 s−1. Flood-frequency relations using the expected moments algorithm, which better incorporates paleoflood data, were developed to assess the risk of extreme floods. Envelope curves encompassing maximum rainfall (181 sites) and floods (218 sites) were developed for northwestern Colorado to help define maximum contemporary and Holocene flooding in Elkhead Creek and in a regional frequency context. Study results for Elkhead Reservoir were accepted by the Colorado State Engineer for dam safety certification.

[1]  S. E. White Rock Glacier Studies in the Colorado Front Range, 1961 to 1968 , 1971 .

[2]  J. Harden A quantitative index of soil development from field descriptions: Examples from a chronosequence in central California , 1982 .

[3]  F. Stermitz,et al.  Floods of June 1964 in northwestern Montana , 1964 .

[4]  Regional analysis of annual precipitation maxima in Montana , 1997 .

[5]  B. Menounos,et al.  Evidence for Cirque Glaciation in the Colorado Front Range during the Younger Dryas Chronozone , 1997, Quaternary Research.

[6]  John E. Costa,et al.  EVALUATION OF THE FLOOD HYDROLOGY IN THE COLORADO FRONT RANGE USING PRECIPITATION, STREAMFLOW, AND PALEOFLOOD DATA FOR THE BIG THOMPSON RIVER BASIN , 1988 .

[7]  P. C. Patton,et al.  Ephemeral-Stream Processes: Implications for Studies of Quaternary Valley Fills , 1981, Quaternary Research.

[8]  R. D. Jarrett Flood Elevation Limits in the Rocky Mountains , 1993 .

[9]  John E. Costa,et al.  Hydraulics and basin morphometry of the largest flash floods in the conterminous United States , 1987 .

[10]  P. Wilcock Flow competence: A criticism of a classic concept , 1992 .

[11]  S. Colman,et al.  Nomenclature of alpine glacial deposits, or, What's in a name? , 1979 .

[12]  E. Hansen Probable maximum precipitation estimates-United States between the Continental Divide and the 103rd meridian , 1988 .

[13]  Jery R. Stedinger,et al.  Surface water hydrology: Historical and paleoflood information , 1987 .

[14]  R. Madole Lake Devlin and Pinedale Glacial History, front Range, Colorado , 1986, Quaternary Research.

[15]  J. B. Benedict Recent Glacial History of an Alpine Area in the Colorado Front Range, U.S.A.: I. Establishing a Lichen-Growth Curve , 1967, Journal of Glaciology.

[16]  M. S. Petersen,et al.  The Black Hills-Rapid City flood of June 9-10, 1972; a description of the storm and flood , 1975 .

[17]  P. Komar Selective gravel entrainment and the empirical evaluation of flow competence , 1987 .

[18]  M. G. Anderson,et al.  Background to palaeohydrology : a perspective , 1984 .

[19]  John Pitlick,et al.  Relation between peak flows, precipitation, and physiography for five mountainous regions in the western USA , 1994 .

[20]  R. D. Jarrett Hydraulics of High-Gradient Streams , 1984 .

[21]  W. Bull Stream-terrace genesis: implications for soil development , 1990 .

[22]  F. Smith,et al.  Response of Bushy-Tailed Woodrats (Neotoma cinerea) to Late Quaternary Climatic Change in the Colorado Plateau , 1998, Quaternary Research.

[23]  J. Doe Friends of the Pleistocene Field Trip , 1986 .

[24]  L. Ely,et al.  Response of extreme floods in the southwestern United States to climatic variations in the late Holocene , 1997 .

[25]  R. J. Tracey,et al.  Precipitation-frequency atlas of the Western United States , 1973 .

[26]  S. Schumm,et al.  Terraces of Douglas Creek, northwestern Colorado: An example of episodic erosion , 1977 .

[27]  H. F. Matthai Floods of June 1965 in South Platte River basin, Colorado , 1969 .

[28]  P. Birkeland,et al.  Soil-geomorphic research — a selective overview , 1990 .

[29]  J. Costa Paleohydraulic reconstruction of flash-flood peaks from boulder deposits in the Colorado Front Range , 1983 .

[30]  L. Vierling Palynological Evidence for Late- and Postglacial Environmental Change in Central Colorado , 1998, Quaternary Research.

[31]  R. D. Jarrett Errors in slope-area computations of peak discharges in mountain streams , 1987 .

[32]  Characteristics of extreme storms in Montana and methods for constructing synthetic storm hyetographs , 1998 .

[33]  A. Kimber Estimating Probabilities of Extreme Floods , 1989 .

[34]  Harry F. Lins,et al.  Streamflow trends in the United States , 1999 .

[35]  J. Costa A history of paleoflood hydrology in the United States, 1800”1970 , 1986 .

[36]  J. R. Wallis,et al.  Regional Frequency Analysis: An Approach Based on L-Moments , 1997 .

[37]  C. Jaworowski,et al.  Quaternary history of some southern and central Rocky Mountain basins , 1991 .

[38]  V. Baker Paleoflood hydrology and extraordinary flood events , 1987 .

[39]  Jeff V. Phillips,et al.  Verification of Roughness Coefficients for Selected Natural and Constructed Stream Channels in Arizona , 1998 .

[40]  W. L. Lane,et al.  An algorithm for computing moments‐based flood quantile estimates when historical flood information is available , 1997 .

[41]  R. D. Jarrett DETERMINATION OF ROUGHNESS COEFFICIENTS FOR STREAMS IN COLORADO , 1985 .

[42]  Ellen Wohl,et al.  Coarse-sediment distribution as evidence of an elevation limit for flash flooding, Bear Creek, Colorado , 1995 .

[43]  Victor R. Baker,et al.  Geomorphological understanding of floods , 1994 .

[44]  S. Elias Late Pleistocene and Holocene Seasonal Temperatures Reconstructed from Fossil Beetle Assemblages in the Rocky Mountains , 1996, Quaternary Research.

[45]  A. Gillespie,et al.  Range fires: A significant factor in exposure-age determination and geomorphic surface evolution , 1991 .

[46]  D. A. Ostenaa,et al.  The Application of a Non-Inundation Approach of Paleoflood Hydrology for the Assessment of Extreme Flood Hazards on the Ogden River, Utah , 1995 .

[47]  R. D. Jarrett,et al.  Paleodischarge of the late Pleistocene Bonneville Flood, Snake River, Idaho, computed from new evidence , 1987 .

[48]  E. Ito,et al.  Holocene Climate in the Northern Great Plains Inferred from Sediment Stratigraphy, Stable Isotopes, Carbonate Geochemistry, Diatoms, and Pollen at Moon Lake, North Dakota , 1997, Quaternary Research.

[49]  J. Harden Soil development on stable landforms and implications for landscape studies , 1990 .

[50]  R. D. Jarrett Paleohydrologic techniques used to define the spatial occurrence of floods , 1990 .

[51]  B. J. Chronic,et al.  Climatography of the Front Range urban corridor and vicinity, Colorado , 1978 .

[52]  P. Birkeland,et al.  Reevaluation of Multiparameter Relative Dating Techniques and their Application to the Glacial Sequence Along the Eastern Escarpment of the Sierra Nevada, California , 1979, Quaternary Research.

[53]  G. C. Lusby,et al.  Runoff and hillslope erosion resulting from a high‐intensity thunderstorm near Mack, western Colorado , 1967 .

[54]  E. Ciolkosz,et al.  A FIELD MORPHOLOGY RATING SCALE FOR EVALUATING PEDOLOGICAL DEVELOPMENT , 1977 .

[55]  A. Gottesfeld British Columbia flood scars: maximum flood-stage indicators , 1996 .

[56]  L. Tieszen,et al.  Phytolith and Carbon Isotope Evidence for Late Quaternary Vegetation and Climate Change in the Southern Black Hills, South Dakota , 1997, Quaternary Research.

[57]  M. Singer,et al.  USE OF A FIELD MORPHOLOGY RATING SYSTEM TO EVALUATE SOIL FORMATION AND DISCONTINUITIES , 1981 .

[58]  Victor R. Baker,et al.  Paleoflood evidence for a natural upper bound to flood magnitudes in the Colorado River Basin , 1993 .

[59]  J. Knox Large increases in flood magnitude in response to modest changes in climate , 1993, Nature.

[60]  B. Richter,et al.  Estimation of natural streamflow characteristics in western Colorado , 1985 .

[61]  John E. Costa,et al.  A comparison of the largest rainfall-runoff floods in the United States with those of the People's Republic of China and the world , 1987 .

[62]  John E. Costa,et al.  Hydrology, geomorphology, and dam-break modeling of the July 15, 1982, Lawn Lake Dam and Cascade Lake Dam failures, Larimer County, Colorado , 1986 .

[63]  J. Lewin Floodplain geomorphology , 1978 .

[64]  Robert D. Jarrett,et al.  HYDROLOGIC AND HYDRAULIC RESEARCH IN MOUNTAIN RWERS , 1990 .

[65]  R. Snipes Floods of June 1965 in Arkansas River basin, Colorado, Kansas, and New Mexico , 1974 .

[66]  J. Stedinger,et al.  Flood Frequency Analysis With Historical and Paleoflood Information , 1986 .

[67]  William J. Elliot,et al.  Critical shear stress and critical flow rates for initiation of rilling , 1993 .

[68]  Peter C. Patton,et al.  Gully Erosion, Northwestern Colorado: A Threshold Phenomenon , 1975 .

[69]  C. Waythomas,et al.  Flood geomorphology of Arthurs Rock Gulch, Colorado: paleoflood history , 1994 .

[70]  H. H. Mills,et al.  Weathering and soil development on fan surfaces as a function of height above modern drainageways, Roan Mountain, North Carolina , 1995 .

[71]  E. Hansen,et al.  Probable maximum precipitation estimates, Colorado River and Great Basin drainages , 1977 .

[72]  R. D. Jarrett,et al.  Roughness Coefficients of Large Floods , 1987 .

[73]  J. B. Benedict Radiocarbon Dates from a Stone-Banked Terrace in the Colorado Rocky Mountains, U.S.A. , 1966 .

[74]  E. Wohl,et al.  Methodology and Implications of Maximum Paleodischarge Estimates for Mountain Channels, Upper Animas River Basin, Colorado, U.S.A. , 1998 .

[75]  E. Hansen,et al.  Meteorology of important rainstorms in the Colorado River and Great Basin drainages , 1981 .

[76]  M. A. Kohler,et al.  Hydrology for engineers , 1958 .

[77]  J. R. Crippen,et al.  Maximum floodflows in the conterminous United States , 1977 .

[78]  Robert D. Jarrett,et al.  Historic-flood evaluation and research needs in mountainous areas , 1994 .

[79]  A. J. Gerrard Soils and landforms: An integration of geomorphology and pedology , 1982 .