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INTRODUCTION This report identifies and describes the flood hazards in the Boulder Creek flood plain from 28th Street in Boulder, Colorado upstream to Arapahoe Road which crosses the stream just outside of the corporate limits of the city. It was originally re. quested by the former Inter.County Regional Plan. ning Commission and later by the City of Bould~r for use in planning for city development and the best future use of lands in flood prone areas. Maps, profiles, and photographs show the effects of floods and the extent of potential future flooC!s under existing conditions. Hydrologic Atlas HA.41 published by the U.S. Geological Survey in 1961 delineates floods at Boulder, Colorado. This current report of the Corps of Engineers updates the prior U.S.G.S. Atlas sinCe it is based on current data - including hydrolo. gic records, topographic mapping and stage of development in the Boulder Creek flood plain. Flood Plain Information, Volume II, BouldN Metropolitan Region covers Boulder Creek down. stream from 28th Street and South Boulder Creek. Plans and recommendations for flood protec. tion projects are not included in this report. The study results may be used, however, to evaluate plans to minimize or avoid future flood losses. Alternatives available may range from special flood prevention projects to a management program utilizing flood plain zoning, building regulation in the flood hazard areas, flood proofing of existing or future structures, and flood insurance. BASIN DESCRIPTION Boulder Creek flows eastward from the high Rockies at the Continental Divide through steep mountain canyons and across the high plains area to St. Vrain Creek a tributary of the South Platte River. The creek drains 440 square miles with about 102 square miles upstream from Boulder. The Boulder Creek channel slope averages 70 feet per mile in the study reach. The creek bed is sand, gravel, and boulders. The flood plain in the study reach is highly developed with commercial and public facilities as well as residential areas. FLOOD HISTORY The record flood at Boulder occured on 31 May through 2 June 1894, the result of heavy rains and snowmelt. Every bridge was washed away and extensive damage done to roads and railroads. Many buildings were damaged or washed away. - - - , . """, ;~ ~ ~ . - ,--- .~ ~- --- ~ '" - .. ...... , .