FLOOD10335 (2) - Laserfiche WebLink

Home Browse Search

!I \1 5 IMIES ASS::JCI.c.:ES 'I \1 Presently, portions of Clear Creek are considered to have a high flood damage potential. The preservation of the floodplain will serve, at least, to maintain the present level of damage potential while any improvements will minimize or reduce the flood damage potential. Reducing the flood hazard potential can be accomplished through structural improvements to bridges and channels, flood proofing, and by an effective floodplain management program I The floodplain limits are based on (1) planned, future development in the basin; (2) existing and mapped floodplain conditions; and, (3) no blockage at the existing culvert and bridge structures. Floods of greater magnitude can and will occur in which the limits of flooding would exceed those shown in the report. 'I This report has identified the probable flooding limits of a potential 1 DO-year flood event drainage basin in Adams County from Sheridan Boulevard to the South Platte River. I n the Clear Creek I SUMMARY Water flowing at a rate greater than 6 to 8 fps will cause severe erosion of stream banks and is capable of transporting large rocks. Velocities in the range of 6 to 8 fps could erode fill around bridge abutments. Water flowing at about 2 fps or less will deposit debris and silt. I -I Average flow velocities characteristic of a 1 DO-year and 1 O-year flood events for Clear Creek are shown on the profile sheets included with the Flood Hazard Area Delineation drawings. In the main reach, the flow velocity in the channel ranges generally between 3 and 19 feet per second (fps) for a 1 DO-year flood event in the study area. Overbank velocities range from 1 to 10 fps. II 'I Flood Velocities A floodway represents a part of the floodplain that is required to pass a 1 aD-year flood event without raising the flood profiles more than an acceptable amount and also represents the part of the floodplain most hazardous to personal safety and welfare. Throughout this study, the floodway was defined for two conditions. The limit of encroachment into the floodplain that raises the existing energy grade line elevations by no more than 0.5 foot and for no more than 1 foot. U.S. Geological Survey, U.S. Army Corps of Engineers Colorado, by Omaha District 1976 Guidelines for 1978B. Hydrology for Determmmg Flood Flow Frequency, Bulletin #17. Clear Creek, Jefferson and Adams Counties I 'I The limits of 1 DO-year flooding for Clear Creek are graphically outlined on the Flood Hazard Area Delineation maps and tabulated in Table 1, Floodplain and Floodway Reference Data. The table lists the potential flood elevations, floodplain and floodway widths, floodway location, floodway surcharge elevation and thalweg elevation at each cross section studied. U.S. Army Corps of III, Clear Creek. National Oceanic and Atmospheric Administration (NOAA), 1978. Precipitation-Frequency Atlas of the Western United States. Volume II, Colorado, U.S. Department of Commerce Engineers 978A. Flood Plain Information Metropolitan Region Denver, CO. Volume ,I The berm on the south side of the main channel downstream of the west crossing of 1-76 was not considered a levee due to inadequate freeboard and was ignored in the delineation per FEMA guidance portion of the mobile home park south of this berm is included in the floodplain. A Landmark Mapping L TO Foot Contour Interval. 1995-1 998 Topographic Mapping, Clear Creek Floodplain Scale 1 '=200'. Two- I The Lowell Boulevard Bridge is not overtopped. However, Lowell Boulevard north of the bridge wi overtopping flows that will pass under 1-76 to the North Overflow floodplain. Gingery Assoc. County, CO. nc. 1979 Flood Hazard Area Delineation Clear Creek, Adams County & Jefferson I North Overflow. These values were incorporated into the model using a lateral weir curve. diverting the flow prior to the Lowell Boulevard Bridge. have Federal Emergency Management Agency, 995. Flood Insurance Study Adams County, CO I I with a rating REFERENCES