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No-Rise/No-Impact Certification September 11, 2018 <tjC Page 3 of 6 The purpose of the this No-Rise/No-Impact Certificate is to determine if the construction of the proposed trail will impact the existing floodway as denoted on the FEMA Flood Insurance Rate Maps (FIRM)that the trail transects. FEMA Flood Insurance Rate Maps (FIRM) The proposed trail transects the following FIRM maps: • 08001 CO2326H dated March 5, 2007 • 08001 CO2327H dated March 5, 2007 • 08001 CO2328H dated March 5, 2007 • 08001 CO2329H dated March 5, 2007 Analysis Procedures The following steps were undertaken to analyze the impact of the trails on the existing floodway: 1. Currently Effective Model TJC obtained the most recent step-backwater hydraulic model for the South Platte River from Urban Drainage and Flood Control District(UDFCD). The HEC-RAS model was prepared in April 2005 by CDM for the South Platte River Flood Hazard Area Delineation (FHAD) Report. Table 1 is the Floodplain and Floodway Data table from the FHAD. 2. Duplicate Effective Model HEC-RAS was used to create a duplicate effective hydraulic model for cross sections 14, 15, 16, 17, and 17.7 of the most recent step-backwater hydraulic model. Plan view of the cross sections modeled are delineated in exhibit A. The Duplicated Effective Model results are an exact match to the Currently Effective Model. Table 2 compares the results of the duplicate model against the FHAD report. Exhibit B contains the cross sections generated for the Duplicate Effective Model. 3. Existing Conditions Model HEC-RAS was utilized to revise the Duplicate Effective Model to reflect existing conditions. Twelve (12) additional cross-sections where added to the model covering the proposed new concrete trail, without the proposed trail in place. New cross sections are approximately 500' apart as shown on exhibit A. The Existing Conditions Model results varied from both the Effective and Duplicate models as denoted below.