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<br />. <br /> <br />THE FLOOD CONTOUR METHOD <br />OF FLOODPLAIN DELINEATION <br /> <br />by <br /> <br />William P. Stanton, P.E. <br />Flood Control and Floodplain Management Section <br />Colorado Water Conservation Board <br />Department of Natural Resources <br />Denver, Colorado <br /> <br />July 15, 1983 <br /> <br />The internal consistency of a regulatory document is <br />important in order to maintain a credible, legally enforceable <br />floodplain management program. For some floodplain studies in <br />Colorado, there appears to be a lack of quality control between <br />the vertical (profile) and horizontal (flooded area map) <br />projections of the delineated floodplain. These discrepancies, <br />which can be fatal to any study, may be eliminated through <br />improved reporting and interpretation procedures. <br /> <br />. <br /> <br />The procedure which the Colorado Water Conservation Board <br />recommends to study contractors and federal agencies for <br />delineation of the floodplain boundaries on'topographic maps is <br />as follows: . . <br /> <br />1. Using the hydraulic analysis, tabulate the flood <br />elevations at each cross section. <br /> <br />2. Draw the flood profiles. <br /> <br />3. Tabulate channel centerline stationing from the water <br />surface profiles at the whole-numbered flood elevations <br />corresponding to the base contour interval elevations of <br />the topographic maps. This is called the plotting <br />table. <br /> <br />4. Mark the location of all flood contours in the channel <br />at the appropriate station along the centerline on the <br />base maps. <br /> <br />5. Extend the flood contours by drawing "wiggly lines" <br />perpendicular to the direction of flow until they <br />intercept their corresponding ground contours. In <br />general, the flood contours should parallel the <br />cross sections and be perpendicular to flow. However, <br />if the cross sections were incorrectly located in the <br />first place, the flood contours may cross them. <br /> <br />. <br /> <br />(over) <br /> <br />175 <br />wsf fm <br />