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<br />. <br /> <br />. <br /> <br />. <br /> <br />VII. HEC-2 HYDRAULIC PARAMETERS <br /> <br />The following is a summary of the various hydraulic parameters which were utilized in the HEC-2 <br />backwater computations, <br /> <br />I, Roughness Coefficients (Mannings nl <br /> <br />The roughness coefficients used for this study are 0,032 for the improved channel section and <br /> <br /> <br />a range between 0.045 to 0,065 was used for the overbank areas, The roughness coefficient <br /> <br /> <br />for the channel was selected based on a native grass lining and a proposed maintenance <br /> <br /> <br />program by the Town which will be reviewed annually by CWCB, <br /> <br />2, Contraction/Expansion Coefficients <br /> <br />The Coal Creek Modeling used 0,1 for the contraction and 0,4 for the expansion along the <br />channel. Transitions, including bridges, were modeled with 0,3 contraction and 0,5 <br />expansion coefficients, <br /> <br />VIII. FINAL REVISED FLOODPLAIN AND FLOODW A Y <br /> <br />The final revised floodplain and f100dway represents the results of the HEC-2 analysis presented <br /> <br /> <br />herein, The existing model for the floodplain was obtained and run to verify the accuracy of the model (see <br /> <br /> <br />Appendices A through D), A summary of the existing 100-year floodplain and f100dway are presented in <br /> <br /> <br />Tables I and 2. respectively, The existing flood way analysis shows a I,I-foot rise in water surface elevation <br /> <br /> <br />at Section 15,0, The increased rise, over the previous study, can be attributed to revisions to the HEC-2 <br /> <br /> <br />computer program and changes in the algorithms used, <br /> <br />The cross-sections were adjusted for the proposed developed conditions, and additional cross-sections <br />were input as needed to model the improvements properly (see Appendices E and F), The proposed drainage <br />improvements and final 100-year floodplain are shown on Figure-4 with final water surface profiles on Figure- <br />5, The HEC-2 model stations is presented in Table-3, <br /> <br />The Hec-2 Analysis begins with 5 sections that will not be affected by the subject improvements, <br /> <br />4 <br />