Laserfiche WebLink
<br />~'I> <br /> <br />. <br /> <br />WORK PLAN FOR THE DEVELOPMENT OF <br />GUIDELINES FOR DETERMINING FLOOD PEAKS FOR <br />APPROXIMATE tOO-YEAR FLOODPLAINS <br /> <br />This Work Plan proposes a process for development a publication entitled "Guidelines for <br />Determining Flood Peaks for Approximate 100- Y ear Floodplains". The Guidelines would provide <br />a methodology for computing approximate lOO-year flood flows for approximate floodplain <br />delineations that were prepared for Colorado stream reaches without hydrologic analyses. The <br />methodology utilizes detailed hydrologic analyses that have already been approved by the CWCB <br />through the designation and approval process. Using data from those already approved <br />hydrologic analyses, regression equations/curves would be developed. Those equations/curves <br />could then be used to compute flows for the stream reaches which currently have no computed <br />flows. <br /> <br />PreDaration of Ref!ression Equations and Curves <br /> <br />. <br /> <br />To begin the process of developing regressions, the state would be divided into <br />geographic regions of relative hydrologic homogeneity and data from designated studies in each <br />region would be collected. The division of the state's major river basins into smaller regions and <br />preliminary efforts to actually do that in the Arkansas River basin are described in the section <br />entitled "Specific Hydrologic Regions". Regressions relating the I DO-year flows in those detailed <br />studies to the corresponding drainage area would be developed for each region. Drainage area <br />and peak flow values for each studied stream reach would be entered into a spreadsheet program <br />and then into the regression program. Data points from the preliminary regional sub-basins <br />would be grouped and tested by graphical interpretation and performing regressions until a <br />correlation of plus or minus twenty percent of the observed values was achieved. Through an <br />iterative process the regression equations would be refmed. Best-fit equations which were too <br />complex would be replaced with simpler equations as long as they fell within a reasonable <br />correlation range. Using the computer regression program entitled "Curvefit", data for streams <br />in the Arkansas River basin were analyzed and preliminary regressions were developed. That <br />program is likely to be used in the implementation of the Guidelines. <br /> <br />Soecific Hvdrolol!ic Rel!:ions <br /> <br />After the currently designated detailed studies for the entire state had been <br />separated into the major basins, the process of subdividing those basins would begin. Using the <br />factors listed above, each major drainage basin studied would be divided into preliminary <br />geographic/topographic groups using 3 generalized divisions: I) plainS', 2) foothills and 3) <br />mountains, It is anticipated that further subdivision beyond those 3 divisions would be needed <br />to develop meaningful regression equations. To date, the only major basin for which this <br />regional subdivision process has been carried to draft form is the Arkansas River basin. <br />Subdivision of the Arkansas River basin required more than 3 regions. The regions for the <br />. Arkansas River basin are shoWn in Figure 2. <br />