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<br /> <br />1803 <br /> <br />Type ill Analysis on five strewn gages as listed above (in accordance with Bulletin 17B, EM <br />1110-2-1415, ER 1110-2-1450 and the HEC-FFA User Manual. <br /> <br />The flow verBUS the drainage area for the 2-, io-, 50- and tOO-year flows was plotted <br />using an Excel spreadsheet. These plots showed that the peak flows for the 10, 50, and 100-year <br />frequency primarily occurred at the La Junta stream gage. The 2-year peak flow occurred at the <br />Nepesta stream gage. The flow typically attenuates downstream as it approaches .the Las Animas <br />stream gage. After discussing these plots with experts at HEC in Davis, California, we decided <br />that some of the missing years of data (flood of 1921) needed to be interpolated and added so <br />that these plots better represent the actual trend of flQws. <br /> <br />The Moments (mean, standard deviation and skew) versus drainage area was then plotted <br />in a spreadsheet for each of the group of statistics. The mean and standard deviation behaved <br />very well (gradual change in slope of the curves) for :the period of record. The skew showed no <br />apparent pattern. <br /> <br />The Moments versus time was used as a tool to investigate how purported changes in the <br />watershed affect the discharge frequency. A trend analysis was to develop by taking the lO-year <br />running moments. First we ran the FFA progrwn using lO-year data sets. Then we plotted them <br />in Excel using the mid-year to define the points. Thci plots showed relatively Bmooth curves. <br />The mean versus time showed a relatively steady trer\d versus time. The Btandard deviation <br />versus time showed an increasing trend versus time, Which is primarily due to the floods of 1999. <br />The plots of the skews were less consistent. <br /> <br />Table 3.2 lists the frequency discharge peaks generated by the FFA program for selected <br />stations on the Arkansas River. <br /> <br /> TABLE ~.2 <br />DISCHARGE FREQl.)ENCY PEAKS <br /> 1O.0'll>- 2.0%- 1.0%- 0.2%. <br /> Drainage Chance Chance Chance Chance <br />LOCATION Area Flood Flood Flood Flood <br /> (sq mil Discharge Discharge Discharge Discharge <br /> (cfs) (cfs) (cfs) (cfs) <br />Arkansas River near Avondale, CO 6327 16500 33600 44400 81900 <br />Arkans.. Ri vcr near Nepe.ta, CO 9345 'L 9700 39000 50600 88500 <br />ArkaIl8as River at Catlin Dam at Fowler, CO 10901 18400 39700 53500 102000 <br />Arkan... River at La lunta, CO t2210 25100 53300 69400 118000 <br />ArkaIl8as River at La. Animas, CO 13976 17700 40100 53800 98500 <br /> <br />28 <br /> <br />3 <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />