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<br /> Peak Flow (Cubic Feet per Second)
<br />-Index Location Drainage Area 10-Year 50-Year 100-Year SOO-Year
<br />Point (Sq. Mi.) Flood Flood Flood Flood
<br />1 Near' Somerset gage 531 5,600 8,000 9;200 11,300
<br />2 Near Bowie (below
<br /> Hubbard Creek) 626 6,300 9,100 10,400 12,800
<br />3 Near Paonia 734 6,900 9,900 11,300 14,000
<br />4 Above Hotchkiss 851 7,600 10,700 12,200 15,000
<br />5 Below Hotchkiss
<br /> (below Leroux Creek) 937 8,100 11,300 12,800 15,700
<br />
<br />Peak flow values for 10-, 50-, 100, and 500-
<br />year floods (together with corresponding water
<br />surface elevations) at each cross section used in
<br />the hydraulic analysis made for this report are
<br />shown in Appendix A.
<br />
<br />Plate 1 is an index to detailed maps (Plates 2-
<br />16) showing the areas that would be inundated
<br />by the loo-year flood. As shown on Plates 3, 4, 9,
<br />and 12, some areas are subject to sheet flow;
<br />that is, broad overland flooding generally less
<br />than 2 feet deep on the average and character-
<br />ized by unpredictable flow paths. Water surface
<br />elevations in sheet flow areas are essentially
<br />independent of those along adjacent stream-
<br />ways and are affected principally by obstruc-
<br />tions and local topography in the area flooded.
<br />
<br />Profiles of the 10-, 50-, 100-, and 500-year
<br />floods are shown as Plates 17-33. Flood eleva-
<br />tions were. computed through use of the Corps
<br />
<br />of Engineers step-backwater program HEC-2.
<br />Basic cross section input was from field survey
<br />data furnished by the Colorado Water Conser-
<br />vation Board and Delta and Gunnison Counties.
<br />Depth of water in the channel and adjacent
<br />flooded areas can be determined from the
<br />profiles.
<br />
<br />Velocity of flow during a loo-year flood on
<br />the North Fork Gunnison River would average
<br />about 7-10 feet per second in the channel and
<br />2-3 feet per second in overbank areas. Water
<br />flowing at 10 feet per second will cause severe
<br />erosion of channels, destroy low water cross-
<br />ings, and transport large boulders. Streambanks
<br />and the fill around bridge abutments may be
<br />eroded, and large amounts of sediment trans-
<br />ported by water flowing at 5-7 feet per second.
<br />Water flowing at about 2 feet per second will
<br />deposit sand, silt, and flood borne debris.-
<br />
<br />5
<br />
<br />I
<br />I FLOOD HAZARD INFORMATION
<br />I NORTH FORK GUNNISON RIVER
<br /> Hotchkiss to Somerset, Colorado
<br />I APPENDIX A
<br />I PEAK FLOWS AND STAGES
<br /> 10-, 50-, 100-, and 500- Year Floods
<br />I (Drainage Area 530 - 940 Sq. Mi.)'
<br />I Peak Flow (Cubic Feet per Second) I Stage (Feet)'
<br /> Cross Section 10- Year Flood 50-Year Flood 100- Year Flood 500- Year Flood
<br />I Number' Location" Flow Stage Flow Stage Flow Stage Flow Stage
<br /> 104 33.980 8,100 5262.5 11,300 5262.7 12,800 5263.1 15,700 5263.6
<br />I 106 34.760 8,100 5265.6 11,300 5266.8 12,800 5267.2 15,700 5267.8
<br />108 35.530 8,100 5268.5 11,300 5269.1 12,800 5269.7 15,700 5270.4
<br />110 38.190 7,600 5280.3 10,700 . 5281.3 12,200 5281.5 15,000 5281.8
<br /> 112 39.620 7,600 5288.5 10,700 5289.8 12,200 5290.6 15,000 5292.0
<br />I 112.1 39.710 7,600 5290.5 10,700 5291.9 12,200 5292.2 15,000 5292.5
<br /> 112.2 39.725 7,600 5291.0 10,700 5292.6 12,200 5293.2 15,000 5294.5
<br />I 114 39.760 7,600 5291.4 10,700 5293.1 12,200 5293.8 15,000 5i95.0
<br />116 40.200 7,600 5292.2 10,700 5293.8 12,200 5294.4 15,000 5295.4
<br />118 41.390 7,600 5298.3 10,700 5299.0 12,200 5299.3 15,000 5299.8
<br /> 118.1 41.730 7,600 5300.4 10,700 5301.1 12,200 5301.3 15,000 5301.8 \
<br />I 120 42.070 7,600 5301.7 10,700 5302.7 12,200 5303.2 15,000 5304.0
<br />122 43.080 7,600 5307.3 10,700 5307.9 12,200 5308.2 15,000 5308.7
<br /> 124 43.700 7,600 5309.6 10,700 5310.5 12,200 5310.9 15,000 5311.5
<br />I 126 44.470 7,600 5313.6 10,700 5314.8 12,200 5315.4 15,000 5316.3
<br />128 44.600 7,600 5315.8 10,700 5317.1 12,200 5317.6 15,000 5318.4
<br /> 129 44.634 7,600 5315.9 10,700 5317.2 12,200 5318.0 15,000 5319.0
<br />I 130 44.730 7,600 5316.7 10,700 5318.4 12,200 5319.0 15,000 5320.2
<br />132 46.370 7,600 5325.6 10,700 5326.6 12,200 5327.0 15,000 5327.7
<br /> 134 47.440 7,600 5332.5 10,700 5333.3 12,200 5333.7 15,000 5334.4
<br />I 136 48.620 7,600 5340.1 10,700 5341.0 12,200 5341.3 15,000 . 5341.7
<br />138 49.950 7,600 5349.0 10,700 5349.8 12,200 5350.0 15,000 5350.7
<br /> 140 50.150 7,600 5351.5 10,700 5353.1 12,200 5353.8 15,000 5355.0
<br />I 141 50.160 7,600 5351.6 10,700 5353.5 12,200 5354.5 15,000 5358.4
<br />142 50.210 7,600 5353.4 10,700 5355.0 12,200 5355.7 15,000 5358.5
<br />I 1At upstream and downstream limits of study reach.
<br />2National Geodetic Vertical Datum, 1929 adjustment. --
<br /> -
<br />'On reportpl'les showing flooded areas (Nos. 2-16) and flood profiles (Nos. 17-33).
<br /> "Distance in thousands of feet upstream from mouth. ---._-
<br /> ---
<br />I 7
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