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<br />. included an estimate of the PMF. The PMF (Cudworth, 1989) is an estimate of the maximum flood potential
<br />for a given drainage basin, The PMF, which is derived from an analysis of the PMP (Hansen and
<br />Schwarz, 1981; Cudworth, 1989), has been used as the design criteria for the capacity of dams and
<br />spillways for about 50 years, Prior to that, a variety of methods were used to obtain the magnitude of the
<br />design flood. However, there is substantial uncertainty and controversy in estimating the magnitude and
<br />frequency of floods, particularly extreme floods in the Rocky Mountains because of complex,
<br />hydrometeorological processes involved and a lack of data on extreme rainstorms and flooding. Henz
<br />(1991) reviewed the use and applicability of current PMP (Hansen and others, 1988) in Wyoming. He
<br />concluded that additional meteorological research is needed to refine estimates of extreme precipitation in
<br />the Rocky Mountains of Wyoming. Buckley (1995) concluded that there are no significant rainstorms even
<br />remotely comparable to the magnitude of the PMP's for mountains in Wyoming. Eastwood (1995)
<br />developed regional relations to estimate extreme precipitation in the mountains of Wyoming. Jensen
<br />(1995) developed new criteria for computing PMP estimates for short-duration, small-area storms in Utah.
<br />His study resulted in significant decreases in precipitation duration and depth for Utah compared to PMP
<br />estimates,
<br />
<br />.
<br />
<br />Two of the most critical assumptions in procedures to calculate PMP are storm transposition of storm
<br />events that could happen at a sliQhtly different location in the same region and moisture maximization
<br />(National Research Council, 1994). Primarily because of the Big Thompson River flood of 1976 in the
<br />Colorado Rockies, which killed about 140 people (McCain and others, 1979), there has been a renewed
<br />interest in improving the knowledge of the hydrometeorology of floods. The primary goal of this research is
<br />to and reduce the uncertainty in estimating the magnitude and frequency of floods throughout the Rocky
<br />Mountains. The National Research Council (1994) recognized that: (1) the greatest deficiency of the
<br />PMP/PMF is for extreme storms in mountain basins less than about 400 mi2, (2) the need for regional
<br />analysis of extreme precipitation and flooding; and (3) the subjectivity and variation of PMP estimates
<br />among experienced meteorologists. In an evaluation of extreme floods and use of the PMF methodology to
<br />estimate design floods, the Interagency Advisory Committee on Water Data (1986) raised a major concem
<br />about the Nation's flood hydrology, whether computed PMF's are either dangerously small or wastefully
<br />large, Therefore, accurately estimating extreme flooding requires a delicate balance between cost and
<br />safety .
<br />
<br />.
<br />
<br />Interdisciplinary flood research in Colorado (Jarrett and Costa, 1983, 1988; Jarrett, 1987, 1990a, 1990b,
<br />in review; Grimm, 1993; Pitlick, 1994; Waythomas and Jarrett, 1994; Jarrett and Waythomas, in press;
<br />Jarrett and others, in review; Pruess, 1996) and in the Rocky Mountains (Jarrett, 1993; Parrett and
<br />Holnbeck, 1994; Buckley, 1995; Eastwood, 1995; Jensen, 1995; Brien, 1996) provides new insight into
<br />the hydrometeorology of extreme flooding in the Rocky Mountains. Grimm and others (1995) indicate
<br />coarse-sediment distribution can be used to help define the magnitude and spatial limits of flooding. In an
<br />analysis of U.S. Geological Survey streamflow-gaging station data in the Rocky Mountain region, which
<br />included slations in New Mexico, Colorado, Wyoming, Idaho, and Montana, Jarrett (1993) identified
<br />maximum unit discharges, which is maximum peak flow divided by drainage area, for streams located
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