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FLOOD INSURAKCE STUDY City of Longmont, CO 1.0 INTRODGCTION 1.1 P~rpose of Study The purpose of this Flood Insurance Study is to investi- gate the existence and severity of flood hazards in the City of Longmont, Boulder County, Colorado, and to aid in the administration of the Flood Insurance Act of 1968 and the Flood Disaster Protection Act of 1973. Initial use of this information will be to convert the City of Lo~gmont to the regular program of flood insurance by the Federal Emergency Management Agency. Further use of the infornation will be made by local and regional plan- ners in their efforts to promote sound land use and flood plain developnent. 1.2 Coordi~atio~ ~he City of Longmont Engineering Department supplied zon- ing and corporate boundary maps and various detailed drawings for channel improvements such as final construc- tion plans for the Spring Gulch Linear Park and storm drainage facilities, dated January 1973, and the struc- tural plans for the Pratt Street bridge, over the St. Vrain Creek. The Longmont Planning Department has sup- plied a copy of The St. vrain Comprehensive Plan (Ref- erence 1), which describes the comprehensive plan for what is called the Prime Urbanized Area of Longmont. The Planning Department also provided a copy of the flood plain a~d =loodway zoning ordinance, and various histori- cal aspects of flooding and community development. Con- ferences were held with the City Planning and Engineer- ing Departments staff on July 23, 1974: May 14, 1975: and December 30, 1975, to discuss detailed aspects re- garding the various streams studied. The 03aha District of the C.S. Army Corps of Engineers provided contour mapping on the St. Vrain Creek and parts of Left Hand Creek, Dry Creek, and Spring Gulch (Reference 2). Corr-puter card input regarding the hydro- logy and hydraulic analyses for the St. Vrain Creek and Left Hand Creek were also provided by the U.S. Army Corps of Engineers. The Flood Plain Information Reports co~pleted by the U.S. Army Corps of Engineers in January of 1969, on Left Hand Creek and in June of 1972, on the Lower St. Vrain Creek, served as an important basis for conparison in this study (References 3 and 4). On October 16, 1974, a conference was held with the Omaha