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FLOOD03824
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Last modified
1/25/2010 6:44:27 PM
Creation date
10/5/2006 12:05:34 AM
Metadata
Fields
Template:
Floodplain Documents
County
Statewide
Stream Name
South Platte, Arkansas, Colorado
Basin
Statewide
Title
Annual Snowmelt and Rainfall Peak Flow Data on Selected Foothills Region Streams, South Platte River, Arkansas River, and Colorado River Basins Colorado
Date
1/1/1982
Prepared By
USGS
Floodplain - Doc Type
Educational/Technical/Reference Information
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<br />usually occurred during the period from May to July at these elevations. Below <br />6,000 to 7,000 ft, streamflow records of the South Platte River and the Arkansas <br />River basins generally revealed an annual snowmelt hydrograph of shorter duration <br />that occurred earlier in the year. The amplitude of daily gage-height fluctuations <br />during snowmelt runoff was less pronounced at these lower-elevation stations than <br />at the higher-elevation stations. <br /> <br />Rainfall runoff from a convective storm or frontal system affects streamflow <br />much more quickly than does meltwater from the snowpack. Therefore, discharge <br />peaks produced by rainfall are less regular in occurrence than snowmelt-runoff <br />peaks. In the foothills region of Colorado, intense precipitation from convective <br />storms may produce flash floods with sudden increases in stage and discharge. <br />This type of runoff is identified in streamflow charts by an abrupt rise in stage. <br />Generally the streamflow peak lasts for only a few hours, and within a few days, <br />the discharge diminishes to the prestorm level, as shown in figure 6. Runoff peaks <br />of this type usually occur in late spring and summer when thunderstorm activity is <br />g rea tes t. <br /> <br />The rainfall hydrograph becomes complex when two or more precipitation events <br />occur within a short span of time, as shown in figure 6, or when intermittent rain <br />falling over several days results in a progressive increase in stage. Uncertainty <br />of the type of streamflow peak was usually resolved by consulting precipitation <br />and temperature records of nearby weather stations. This information is published <br />monthly for the State of Colorado by the U.S. National Oceanic and Atmospheric Ad- <br />ministration (1961-77). <br /> <br />Once peaks were determined for snowmelt runoff and rainfall runoff, the asso- <br />ciated discharges were computed by conventional means from the applicable rating <br />tables. When a snowmelt-runoff or rainfall-runoff peak was also determined to be <br />the annual runoff peak, data were used from published U.S. Geological Survey Water <br />Supply Papers or U.S. Geological Survey Water Resources Data for Colorado reports. <br /> <br />Unusua I S i tuat ions <br /> <br />A discretionary classification of streamflow records was required when peak <br />flows were caused by a combination of meteorologic factors. In a number of cases, <br />a rainfall-runoff peak occurred at a time when streamfiow included snowmelt run- <br />off. When the rainfall occurred early in the season during a period of large di- <br />urnal discharge, and if runoff contributed by rainfall was small relative to that <br />of the total streamflow, as shown in figure 7, gage height A, the resulting runoff <br />peak was classified a snowmelt-runoff peak. If the runoff contributed by rainfall <br />was large relative to the total streamflow, the peak was classified as a rainfall- <br />runoff peak, as shown in figure 7, gage height B, <br /> <br />In some cases, particularly at higher elevation stations, runoff from a rain- <br />fall event was a very small part of the total streamflow, but because it was the <br />only rainfall runoff recorded for the year, it was classified as the annual rain- <br />fall-runoff peak. <br /> <br />11 <br />
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