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<br />draft 3120/98 <br /> <br />paleoflood study results are in bedrock channels (Kochel and Backer, 1982: Jarrett and Malde, 1987: <br /> <br /> <br />Waythomas and Jarrett, 1994), and where the channels are shown to be stable for long time spans <br /> <br /> <br />(Jarrett, in review). <br /> <br />A critical issue for the reliability of paleo/lood investigations has been representativeness of the <br /> <br /> <br />height of PSIs as proxies for peak-/lood stage. Generally, the elevation at the top of the /lood- <br /> <br /> <br />deposited sediments is assumed to represent a minimum estimate for the maximum paleo/lood stage <br /> <br /> <br />responsible for emplacing sediments (Kochel and Baker 1982; Baker, 1987; Knox, 1988; O'Connor <br /> <br /> <br />et al., 1994). Some investigators have calculated estimates of water above the top of /lood-deposited <br /> <br /> <br />sediment using /low-competence relations (Costa, 1983: Baker, 1984; Knox, 1988; Levish et al, 1994; <br /> <br /> <br />Waythomas and Jarrett, 1994), but these relations are not always accurate (Costa, 1983; Komar, 1987; <br /> <br /> <br />Wilcock, 1992). One way to assess the validity of these assumptions is to document and determine <br /> <br /> <br />the relation between the elevation of PSIs and HWMs of recent large /loods (Jarrett and Costa, 1986: <br /> <br /> <br />House et al., 1995; Springer and Kite, 1997). In this paper, we conduct a comprehensive analysis for <br /> <br /> <br />recent /loods (1991-98) in the western United States to provide quantitative information for the <br /> <br /> <br />reliability of PSIs. <br /> <br />Methods <br /> <br />There are many factors that contribute to flood-deposition including sediment sizes available for <br /> <br /> <br />transport, hydraulic characteristic of the /low, and the geometry and roughness of local depositional <br /> <br /> <br />environments (Costa, 1983; Baker, 1984; O'Connor, 1993). We attempt to quantify as many of these <br /> <br /> <br />characteristics as possible, but the most critical requirement was obtaining the actual peak-/lood <br /> <br /> <br />height at the location of associated /lood-deposited sediments. HWMs are physical evidence such as <br /> <br /> <br />bent grass, mud, silt, and seed lines, and /lotsam, particularly fine organic debris, that document the <br /> <br /> <br />peak stage ()f a recent /lood, but usually are not preserved for more than a few weeks to months <br /> <br /> <br />(Jarrett, 1984; Williams and Costa, 1988). Conversely, recent /lood-deposited sediments (or new <br /> <br /> <br />PSIs) can be preserved for long time spans, We also verified that /lood-deposited sediment resulted <br /> <br /> <br />from the recent /lood. In most cases, there was little difficulty because fresh sediments were <br /> <br />5 <br />