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<br />INTRODUCTION <br /> <br />Puroose <br />This Floodplain Information Report was prepared to provide the Colorado Water <br />Conservation Board with appropriate data for select USGS and DWR stream flow gages <br />throughout Colorado. Information is provided displaying the available peak flow values <br />(from published and calculated floodplain studies) for streams where snowmelt nmoffis <br />expected or has historically occurred. This stream gage information was compared with <br />published studies to identify gaps in flood-frequency information. Using all the compiled <br />information, it is now possible to estimate appropriate a1ann levels for high nmoff at each <br />of the stream gages located along critical stream reaches. This effort will be used to <br />support the state's ALERT system. <br /> <br />This Floodplain Information Report includes: <br /> <br />I. Various engineering methods to determine the 100- Y ear and 1 0- Year Flood <br />Flows <br /> <br />2. Final spreadsheet with compiled information <br /> <br />3. Flood Frequency Analysis Program Input and Output information <br /> <br />STREAM FLOW DATA <br /> <br />USGS Website Information <br />To obtain the 10-Year and 100-Year Flood Flows for selected stream gages throughout <br />Colorado, it was possible to collect information from the USGS website. This search was <br />used using the appropriate county for the gage. Previous floodplain documents had been <br />published that reported the 100 and 10 Year Flood Flows. This information was <br />inventoried and tabularized in an Excel spreadsheet. The website used is as follows: <br />http://cwcb.viis.state.co.us/cwcbimaging.htm. <br /> <br />Ratio Calculations <br />For a lot of different stream flow gages, only the 100- Y ear Flood Flow was given. <br />Therefore, it was necessary to calculate the 1 0- Year Flood Flow. In order to do this, an <br />average ratio was calculated. For the stream gages that had both the 100 and 10-Year <br />Flood Flows, a flow ratio was calculated by dividing the I 0- Year Flood Flow by the 100- <br />Year Flood Flow. Once all of the possible ratios were calculated, then they were all <br />averaged together to get one flow ratio. For this particular stream flow data report, the <br />average flow ratio was 0.4829377116. This average flow ratio was then multiplied by the <br />1 00- Year Flood Flow to get the missing 10- Y ear Flood Flow information. <br />