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.---......... ~-m.$, 'Af'';''1WJi7-,' ~<"~1}F 2972 JARREIT AND TOMLINSON: REGIONAL INTERDISCIPLINARY PALEOFLOOD METHOD Table 2. (continued) DA, Elevation, S, Width, Depth, Site Stream kIn' m mm-1 m m White River 85 Sheep Creek near Meeker 49 1905 0.01 7.6 1.5 86 Flag Creek near Meeker 135 1920 0.01 9.1 1.5 87 White River near Meeker 2093 1905 0.003 45.7 2.4 White River near Meeker 1995 peak 2093 1905 41.1 1.7 White River near Meeker 1995 peak 2093 1905 88 Curtis Creek near Meeker 41 1948 0.Ql 9.1 0.9 Abbreviations are as follows: S is estimated water slope at site. Percent difference is Q gage percent difference of 1995 peak discharge estimated using paleoflood techniques from high-water marki and at the streamflow-gaging station independently obtained from a wellwdefined stage- discharge relation. Q% is estimated total uncertaintf of paleoflood discharge estim3;te given in percent. Q/A is unit discharge. Dbed is maximum particle size on the streambed available for transport. D lOB is maximum particle size transported to the flood bar. Type is type of evidence used to determine peak discharge. FB is bouldery flood bar, NI is noninundation surface, HWM, high-water mark, and GAGE is streamflow-gaging station. RD method is the method used which consicers degree of soil development (5), surface-rock weathering (W), surface morphology (M), lichenometry (L), and boulder burial (B), although not all methods could be used at each site. Numerical values from Table 1 are listed for each RD method. Age is the composite agc for the paleoflood record length. Reliability is the estimated uncertainty of composite age; positive value only indicates age may be longer by this amount. Abbreviations with streams are as follows: DA, drainage area; Me, main channel; OB, overbank; and LB, left bank. UDefinitions of numerals arc as follows: 1, no subitantial flooding on floodplain; 2, water too deep to estimate particle size or unavailable; 3, flood caused by dam failure; and 4, underfit stream. here in attempting to identify the paleoflood record length for the largest flood during the Holocene, such uncertainties can he addressed in the EMA flood-frequency anllyses. Soil development, boulder weathering, and surface mor- phology seemed to have Ihe best consistency (Table 2) and thus potential for assigning ages either individually or com- bined. Available soil and surficial geology repc'rts for the study area ISoil COllsen'atiofl Sen'ice, 1982; Madole, 1982, 1989, 1991b, 1991c; Nall/ral Resources Conservation Service, 2000J were helpful in assigning ages, particularly for NI surfaces. However, ncar-stream alluvial deposits with extensive soil de- velopment sometimes were mapped as fresh alluvial deposits. This was attributed to the fact that the primary purpose of soil surveys is the determination of agricultural productivity or building site potentiaL Thus floodplains may have received less attention during mapping. Boulder burial had a fair consis- tency in the study area. However, it appeared to have more variability; because compared to boulder burial data in the Front Range of Colorado [Way/homos and Jarrett, 1994]. there is usually much more fines deposited around the cobble and bouldery material during flooding. Thus there is some "age" immediately after flooding. Lichenometry, while having poten- Figure 6. Small, low-relief, ftood-bar deposits define the maximum paleostage indicator (PSI) for Elkhead Creek downstream from North Fork E1khead Creek. The view is downstream and toward the left bank; line denotes location of cross section in Figure 7. Well-developed alluvial and colluvial soils (Table 2) on the valley fioor define the noninundation surfaC'e for the maximum PSI range. Paleoflood discharge is 85 m3 S-1 (:=25%) in about 5000 years (:::1000 years).