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, I. . Flood Plain Analysis Report For Fountain Creek Overflow Downtown Pueblo Pueblo, Colorado Job No. 5117001 February, 1983 I. PURPOSE: . The purpose of this report is to document the calculations and present the results of a restudy of the Fountain Creek diversion into downtown Pueblo at the Eighth Street Bridge for the 100-year flood event. This report prepared for the City of Pueblo super- cedes previous diversion calculations developed by the U.S. Army Corps of Engineers (USACOE). LOCATION OF STUDY . This report includes a 100-year floodplain analysis for Fountain Creek at the City of Pueblo, Colorado to determine the flood di- version into the downtown business district for the 100-year flood event. This report includes a detailed study of Fountain Creek from the upstream side of 4th Street to a point approxi- mately 4800' upstream of 8th Street. This report also includes a detailed determination of the 100-year flood diversion into down- town Pueblo and documents the extent of the flooding from the di- version origin at 8th Street to the outlet at Runyen Field. . PREVIOUS ANALYSES . Several previous studies have been prepared for Fountain Creek at the City of Pueblo, Colorado and address the 100-year diversion into the Downtown Business District. The latest study prepared by the U.S. Army Corps of Engineers in 1977 was proposed to su- percede other previous determinations. . Review of the 1977 USACOE calculations show a detailed HEC-2 floodplain analysis of Fountain Creek and hand calculations of the diversion into the downtown area. Utilizing the calculated diversion 100-year flow of 5000 cfs the USACOE developed a HEC-2 model for the downtown area and calculated the diversion flood elevations. According to FEMA Guidelines this downtown flood- plain was calculated to be a 100-year AD zone sheet flooding area with average depth of water from 2-3'. . . During the preparation of the Pueblo Flood Insurance Study Revi- sion by MSM/SP Group, it was observed that questionable coding was found in the USACOE HEC-2 model for Fountain Creek. This questionable coding included the following: 1. Double skew factor for bridge data and single skew for cor- responding ground at the Eight Street Bridge. . -1-