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  <br />5    <br />  <br />2.3 Analysis and Review of Model Results <br />The consultant will use model results from Task 2.2 to prepare GIS based maps that illustrate <br />simulated velocity, depth, and water surface elevations for each flood. These figures will be <br />used to identify flood hazard areas and to support the geomorphic assessment. <br />The consultant shall use the model results to develop public safety depth-velocity hazard maps <br />for two of the five floods using criteria developed by the US Bureau of Reclamation described in <br />1988 Technical No. 11 Downstream Hazard Classification Guidelines. The floods to be mapped <br />will be determined after the results of the five events are reviewed. <br />Water surface elevation and inundation extents for the 1.0 and 0.2 percent annual chance <br />events will be compared to the effective FEMA maps to determine if the results are significantly <br />different. The effective FEMA maps are a composite of two different FEMA studies. In 2021 <br />FEMA completed HEC-RAS 1D hydraulic modeling of the lower 5.5 miles of the Easton Reach <br />to support Countywide floodplain map updates, while mapping for the upper 6 miles of the reach <br />is based on a study published in 1981. <br />The consultant and County staff will meet to review the model results to identify and discuss <br />flood hazard areas and to determine whether the FEMA maps should be updated through a <br />Letter of Map Revision (LOMR). Compilation and submittal of a LOMR request is covered by <br />optional Task 4 below. <br />Deliverables: <br /> Model results – velocity, depth and water surface elevations presented as GIS layers <br /> Graphics showing differences in water surface elevations and flood inundation extents <br />between this study and the effective FEMA maps. <br /> Depth-velocity hazard maps for two events. <br />Assumptions: <br /> Deliverables will be presented in a meeting with County staff and in the project report. <br />The meeting is included in Task 10 below. <br /> Final floodplain inundation and depth-velocity hazard maps will be provided to the <br />County in a format that can be uploaded to the County’s existing GIS database. <br />2.4 Bridge Hydraulic Evaluation <br />Three private bridges cross the river within the project reach – the McElroy Road Bridge, the <br />Sun Island Road Bridge, and the Ellensburg Cement Products facility bridge. Each bridge will <br />be included in the hydraulic model developed under Task 2.2. For Task 2.4 the model will be <br />updated to remove the bridges and associated road fills and then run to simulate the peak flow <br />hydrographs developed under Task 2.1. Model results (without bridge) will be compared to <br />results from Task 2.2 (with bridges) to understand the impact each bridge has on flooding. GIS <br />figures will be created to show differences in velocities, depth, water surface elevations, and <br />flood inundation extents for up to three of the five flood events. The consultant shall use this <br />information to evaluate whether each bridge provides adequate conveyance capacity or <br />constricts flow in a manner that impacts access and evacuation capabilities, which would create <br />additional risks to the public, residents, emergency responders, structures and infrastructure.