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and floodplain areas. Roughness values for the main channels of the streams studied range from 0.020 to 0.065 with floodplain roughness values ranging from 0.020 to O.lOO. Starting water-surface elevations were based on hand at control sections; obtained by the slope area determined for a tributary to a major stream from the at concurrent flows. calculations method, or major stream In the City of Federal Heights, an approximate floodplain analysis was carried out for Niver Creek and Tributary L of Niver Creek using assumed depths based on a review of the Tributary M profile and available hydrologic information, extensive field reconnaissance, and engineering judgment. Through the City of Thornton, the approximate lOO-year flood elevation of Niver Creek and Tributaries Land M were based on the Phase B report, Water and Drainage at Niver Creek (Reference 44), and supplemental data provided by the City of Thornton. The approximate lOO-year flood elevations along Northfield Creek (Hoffman Drainageway) were based on the Interim Drainage Study of Hoffman Way (Reference 45), the Adams County Flood Insurance Study (Reference 2), and additional data provided by the engineering department of the City of Thornton. Approximate lOO-year flooding along portions of Hidden Lake Drainageway were taken from the UDFCD study for that drainage system (Reference 46). For the remaining approximate studies, elevations were determined by normal depth calculations using approximate cross sections taken from USGS maps (Reference 34). Locations of selected cross sections used in the hydraulic analyses are shown on the Flood Profiles (Exhibit 1). For stream segments for which a floodway was computed (Section 4.2), selected cross section locations are also shown on the Flood Insurance Rate Map (Exhibit 2). The hydraulic analyses for this study were based on unobstructed flow. The flood elevations shown on the profiles are thus considered valid only if hydraulic structures remain unobstructed, operate properly, and do not fail. All elevations are referenced to the National Geodetic Vertical Datum of 1929 (NGVD). Elevation reference marks and the descriptions of the marks used in this study are shown on the maps 4.0 FLOODPLAIN MANAGEMENT APPLICATIONS The NFIP encourages State and local governments to adopt sound floodplain management programs. Therefore, each Flood Insurance Study provides lOO-year flood elevations and delineations of the lOO- and 500- year floodplain boundaries and lOO-year floodway to assist communities in developing floodplain management measures. 32