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A reservoir design that must rely on short-term data may be annual peak flows,they may not be representative of condi- <br /> over or under designed.For example,the Folsom Dam and tions experienced over longer periods.Multi-decadal ocean <br /> Reservoir was constructed in the 1950s on the American River temperature variability(as represented by the Pacific Decadal <br /> east of Sacramento,California. Its size was based on stream- Oscillation and the Atlantic Multidecadal Oscillation)has <br /> flow data from about 1905 to 1940.Recent flood studies using influenced streamflows in parts of the United States (Tootle <br /> more years of data indicate that the reservoir is undersized for and others,2005).An example of the potential difference <br /> the desired level of flood protection; costs to retrofit the dam between design flood flows(calculated using Interagency <br /> are about$1 billion(Hester and others,2006b). Advisory Committee on Water Data(1982)guidelines)for a <br /> Design flood flows in the United States are usually calcu- shorter period and for a longer period is shown in figure 2.The <br /> lated with statistical methods that use annual peak streamflows 100-year peak flow based on 66 years of data(1947-2012)is <br /> (Interagency Advisory Committee on Water Data, 1982). If 14 percent higher than the 100-year peak flow based on the <br /> the design flood flows are based on relatively short periods of first 25 years of data(1947 to 1971). <br /> 1500 1200 900 600 <br /> 600 <br /> - _ <br /> -.J <br /> T <br /> ~s. <br /> 45° <br /> p 0 0 AA , <br /> ' p 0 <br /> ZP <br /> a o o ZSAN z2' o <br /> o - <br /> o m� <br /> 300 A <br /> 0: <br /> 1 <br /> Basemap source:Esri,DigitalGlobe 0 500 1,000 MILES <br /> North American Datum 1983,Contiguous USA Albers <br /> EXPLANATION 0 500 1,000 KILOMETERS <br /> 0 U.S.Geological Survey 2009 Hydro-Climatic Data Network(HCDN-2009)streamgages <br /> 0 U.S.Geological Survey HCDN-2009 streamgages supported by the National Streamflow Information Program(NSIP) <br /> 0 Environment Canada Reference Hydrometric Basin Network streamgages <br /> Figure3. Location of streamgages in North America with at least 40 years of data that are suitable for analysis of climate-related trends. <br />