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<br />1200 MDT, and of evapotranspiration and infiltration (particularly in Horse- <br />shoe Park), Errors in the methods of determining the respective volumes (such <br />as surveyi ng and mappi ng errors) and estimates of nonfl ood i nfl ow to Lake <br />Estes also may have contributed to these differences, <br /> <br />Velocities, Depths, Widths, and Areas <br /> <br />The most destructive components of the flood were high shear stresses and <br />high flow velocities, These high velocities, particularly on the Roaring <br />River and the Fall River immediately below Cascade Lake dam, increased the <br />flood's capacity to erode and transport sediment, resulting in severe channel <br />erosion and transport of debris and streambed material (fig, 10). No direct <br />flow velocities were available; however, average velocities, ranging from <br />3,3 ft/s to 12,6 ft/s, were computed by indirect-discharge methods and based <br />on model results are shown in table 4. <br /> <br />In general, velocities increased in the downsteam direction, except <br />through Horseshoe Park and downstream from river mile 10,28. Maximum depths <br />ranged from 6 A to 23.8 ft; maxi mum wi dths ranged from 97 to 1,112 ft <br />(table 4), Cross-sectional areas ranged from 710 ft2 to 2,980 ft2, generally <br />decreasing downstream, except through Horseshoe Park. Cross-sectional data <br />for 14 cross sections and water-surface elevations from which depths, widths, <br />and areas were determi ned are shown in fi gures 55 to 70 in the Supp 1 ementa 1 <br />Cross-Section Data at the end of the report. These cross sections reflect <br />conditions after the flood, Elevations in most cross sections were surveyed <br />to approximate mean sea level (from topographic maps), unless stated as being <br />mean sea leveL Field-estimated Manning's n-values are shown, A question <br />mark follows the values, if conditions (generally scour or debris) indicated a <br />very approximate estimate. <br /> <br />Flood Profiles and Boundaries <br /> <br />In addition to the indirect-measurement site cross sections, high-water <br />marks were obtained at 12 cross sections from which flood profiles could be <br />determined and are shown in Supplemental Cross-Section Data. Because of the <br />relatively shallow depths of flow and extremely high-channel gradient <br />(fig. 2), flood profiles cannot be shown adequately at a realistic scale, The <br />Colorado Water Conservation Board conducted a study to outl ine the flood <br />profiles and boundaries downstream from Rocky Mountain National Park to Lake <br />Estes (W. p, Stanton, Colorado Water Conservation Board, written commun., <br />1982), Flood profiles and boundaries for Estes Park for the July 15, 1982, <br />flood are shown in a report by the Colorado Water Conservation Board (1983). <br /> <br />Flood Frequency <br /> <br />It is of interest to know the re 1 at i ve frequency of the occurrence of a <br />flood, Since this flood resulted from dam failures rather than natural <br />causes, fl ood frequency is not di rect ly app 1 i cab 1 e, However, knowi ng the <br />relative frequency can be useful in illustrating the catastrophic nature of <br />this type of flood and its channel-changing processes, related to historic and <br /> <br /> <br />26 <br />