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<br />Friday. July 12 <br /> <br />10:30 a.m.-12:00 noon <br /> <br />. <br /> <br />paleostage indicators (PSIs). The most commonly used PSI in paleoflood studies of higher- <br />gradient streams (say gradients larger than 0.001 mlm) are flood bars, which are comprised of <br />sands, gravels, and boulders. These bars are preserved for many tens of thousands of years until <br />larger floods produce larger bars. Typically, the elevation of the flood bar is used as the <br />minimum elevation of the flood that deposited the bar. <br /> <br />Hydrologic condition during the 1995 allowed for an elevation of the relation between PSIs and <br />1995 high-water marks (HWMs). <br /> <br />Colorado had one of the driest winters in decades through March 1995 with snowpack in many <br />basins only 50 percent of normal. However, record precipitation occurred from March through <br />June and mostly as snow, which resulted in a record snowpack in many basins in Colorado. <br />Near to record runoff occurred in many streams during June and July, which mobilized and <br />transported large quantities and sizes of bed material. These sediments were deposited as bars <br />in the channel and on the flood plain; many bars were observed forming during peak-flow <br />conditions. The bars contain sand through boulder sized material. Surveys of these bars, <br />HWMs, and channel geometry were made for more than 25 streams that have a wide range of <br />widths, depths, slopes, and particle sizes. In all but the steepest streams, the elevation of the <br />top bar (pSI) essentially is the same as the HWMs. In streams having gradient larger than about <br />0.04 mlm, the top of the bars protruded above the HWMs. Thus, the elevation of flood bars <br />preserved in channel and on flood plains are reliable indicators of the maximum flood stage and <br />thus discharge. These results also provide valuable insight on sediment-transport processes, <br />which are complex and poorly understood in mountain rivers. <br /> <br />. <br /> <br />Examining Alternative Frequency Analysis Procedures <br />Based on Systematic, Historical, and Paleoflood Data <br /> <br />Jose Salas, J. J. England, W. Lane <br />Department of Hydrology <br />Colorado State University <br />and <br />R. D. Jarrett <br />U.S. Geological Survey <br /> <br />The use of historical and paleoflood data, in addition to systematic flood record, has become, . <br />in many instances, an important part of flood frequency analysis. Historical and paleoflood data <br />arise from many sources and in different forms depending on the particular case at hand. <br />Accordingly, a number of techniques have been suggested for empirical frequency analysis based <br /> <br />17 <br />