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<br />Peak discharges on the Arkansas River and Anderson and King Arroyos <br />were developed by the u.s. Army Corps of Engineers (Reference 4). <br />The analysis was based on a regional relationship of basin area to <br />peak discharger using U.S. Water Resources Council guidelines <br />(Reference 5) and streamflow data compiled by the u.s. Geological <br />Survey (References 6, 7r 8, and 9). <br /> <br />Peak discharges for Timpas Creek were provided by the Colorado <br />Water Conservation Board (Reference 2). <br /> <br />Peak discharges for floods of the selected recurrence intervals on <br />the Arkansas River, Anderson and King Arroyos, and Timpas Creek are <br />summarized in Table 2. <br /> <br />3.2 Hydraulic Analyses <br /> <br />Analyses of the hydraulic characteristics of flooding from the <br />sources studied were carried out to provide estimates of the eleva- <br />tions of floods of the selected recurrence intervals. <br /> <br />Water-surface elevations for floods of the selected recurrence <br />intervals were computed using the u.s. Army Corps of Engineers HEC-2 <br />computer program (Reference 10). <br /> <br />Cross section data for those streams analyzed by detailed methods <br />were developed from topographic maps (Reference 11) and field sur- <br />veys. <br /> <br />Structural and elevation data for all bridges and culverts were <br />either provided by Otero County or were obtained by field surveys. <br /> <br />Locations of selected cross sections used in the hydraulic analy- <br />ses are shown on the Flood Profiles (Exhibit 1). For stream seg- <br />ments for which a floodway was computed (Section 4.2) r selected <br />cross section locations are also shown on the Flood Boundary and <br />Floodway Map (Exhibit 2). <br /> <br />Hydraulic roughness coefficients (Manning's "n") were based on <br />field investigations. Roughness values ranged from 0.030 to 0.040 <br />for the channels and from 0.032 to 0.090 for the overbank areas of <br />the streams studied by detailed methods. <br /> <br />Starting water-surface elevations for the Arkansas River were ob- <br />tained using the slope-area method. Starting water-surface eleva- <br />tions for Anderson and King Arroyos and Timpas Creek were taken <br />from the flood profiles for the Arkansas River. <br /> <br />All elevations are referenced to the National Geodetic Vertical <br />Datum of 1929 (NGVD). Elevation reference marks used in this study <br />are shown on the maps. <br /> <br />7 <br />