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<br /> - ~ URS Greiner Woodward Clyde <br /> have been calibrated to real storm events, the peak discharge values would be likely to be <br /> accepted by FEMA if hard copies of the calibration and verification model outputs are <br /> attached along with the application. The peak flow rates for different recurrence design <br /> storms for the upper portion of the Amazon Creek will be obtained from the previous FIS <br /> study. These peak flow rates will be compared with the peak flows generated by the <br /> existing XP-SWMM models or the new runoff model to determine if they can be used as <br /> input in the hydraulic analyses. <br /> Task 3: Hydraulic Analysis <br /> URS will develop the following HEC-RAS models to perform the hydraulic analyses: <br /> Model 1. A duplicate effective model will be re-created based on the HEC-2 input data <br /> from the FEMA library. The same multi-frequency discharges (10-, 50-, 100- <br /> and 500-year) from the FIS will be used in the model to create profiles that <br /> match the profiles in the FIS. This re-created hydraulic model will be used to <br /> produce the effective tie-in conditions. <br /> Mode12. A current conditions model will be developed by extending the duplicate <br /> effective model to include the Lower Amazon Creek including the Diversion <br /> Channel, A3 Channel and Greenhill Tributary downstream of Terry Street to <br /> represent the pre-project conditions. The current conditions model will <br /> incorporate the effective tie-in and represent the 1998 conditions at the site <br /> (i.e., channel conditions without 1135 project in place) for the study area. The <br /> ~r modeling results will be the water surface profiles for the pre-project <br /> conditions for the multi-frequency design discharges (10-, 50-, 100-, and 500- <br /> year). <br /> Mode13. Apost-project conditions model will be developed to evaluate the impact of <br /> the 1135 project. The post-project conditions model will be modified from <br /> the current conditions model to reflect the proposed changes for the channel <br /> associated with the project. <br /> The water surface profiles, floodplain areas and floodway areas between Model 2 and <br /> Model 3 will be compared to determine the impacts of the project. If it is determined that <br /> the 1135 project has no negative impact (i.e., increasing flood elevations, changing <br /> floodway locations, etc.), the results from the post-project conditions model will be used <br /> to perform the floodplain and floodway identification. It is our understanding that the <br /> 1135 project was designed so that the 100-year flood would be contained within' the <br /> newly constructed levee (at least 1 feet below the top of the levee), and all the property <br /> within the levee belongs to the City. The extent of impact would most likely be minimal. <br /> The preliminary cost estimates listed in Table 2 are based on the assumption of no <br /> significant modifications in floodplain and floodway for the previous FEMA study area <br /> and LOMR applications. Additional tasks and budget may be needed if significant <br /> floodplain and floodway changes need to be made for the Amazon Creek upstream of the <br /> Southern Pacific Railroad or a CLOMR is required. <br /> \\Por2\PROI-WC1945(M2na\TASK03001AMAZOMFEMA\fema.dce 4:08 PM 02/25/IXI Page 5 <br /> <br />