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<br />draft 3/20/98 <br /> <br />deposited over live brush or grass. We restricted our analysis to new flood deposits that were at least <br /> <br /> <br />100 mm thick and covered at least 3 m2 because only substantial accumulations are likely to be <br /> <br /> <br />preserved in the stratigraphic record. If the flood was not directly observed, deposit morphology and <br /> <br /> <br />sedimentologic characteristics (Williams and Costa, 1988; Waythomas and Jarrett, 1994) were used to <br /> <br /> <br />differentiate waterflow deposits from those that may have been deposited by debris flows. <br /> <br />After flood runoff receded, extensive post-flood surveys were made. At each site, we measured <br /> <br /> <br />channel geometry for one to five cross sections. multiple HWMs to determine water-surface slope, <br /> <br /> <br />deposit morphology, bed-material sizes, and maximum-clast sizes deposited by the flood. Onsite <br /> <br /> <br />visits were made to as many recently flooded streams primarily in the western United States (AK, AZ, <br /> <br /> <br />CA, CO, MT, NE, NM, NV, UT, WV, and WY) as feasible during 1995-1998 to obtain the necessary <br /> <br /> <br />data. Streams where PSI-HWM data were collected have drainage areas ranging from less than I ktn2 <br /> <br /> <br />to about 63,000 km2. Notable recent floods documented include the: January 1996 flood in the <br /> <br /> <br />Cheat River, West Virginia, about a 100-yr flood (S. Kite, U. of West Virginia, pers. commun., 1997); <br /> <br /> <br />March 1996 flood release from Glen Canyon Dam on the Colorado River, Arizona (Konieczki, et al., <br /> <br /> <br />1997); June 1995 flood on the North Fork Flathead River near Columbia Falls, Montana that was <br /> <br /> <br />slightly larger than a loo-yr flood (C. Parrett, USGS, writt. commun., 1998); July 1996 flash flood in <br /> <br /> <br />Buffalo Creek, Colorado, about a 1O,0000yr flood (Jarrett and Browning, in review); January 1997 <br /> <br /> <br />floods in east-central California and west-central Nevada, which several streams had larger than 100- <br /> <br /> <br />yr floods CR. Meyer, USGS, written commun. 1997); and two floods in July 1997 in northeastern <br /> <br /> <br />Colorado, including the Fort Collins flood (Grimm, 1998), at least 5oo-yr floods (T. Browning, <br /> <br /> <br />Colorado Water Conservation Board, writt. commun" 1997). <br /> <br />6 <br />