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+WATERSHED <br />SCIENCE & ENGINEERING April30,2024 <br />Assumptions: <br />. City and County staff and the CPT will support the collection of data, photos, and accounts of <br />flooding. <br />. Except for GIS flood history data, no new data will be created in this task. <br />. The climate change evaluation will be qualitative and descriptive and will not be modeled unless <br />it is determined necessary and sufficient budget remains, as directed by the City's and County's <br />project manager. <br />Deliverables: <br />. WSE contributions to the draft and final City Conditions Memo. <br />Tosk 2.4. Stormwoter Model <br />WSE will not have any specific tasks related to the stormwater model <br />Task 2.5. Updote Hydraulic Model <br />WSE will update and refine the existing HEC-RAS 2D hydraulic model of Whiskey and Mercer Creek <br />within the City of Ellensburg using data gathered in Tasks 2.2 and 2.3. The model will comply with the <br />FEMA guidelines and standards for flood risk analysis and mapping. <br />WSE will update the modelto: <br />o lncorporate new topographic data and survey identified or collected ln Task 2.2 <br />. Refine model mesh to improve model resolution based on flood mapping analysis completed in <br />Task 2.3 <br />r lncorporate significant stormwater inflow and/or outflow locations modeled in Task 2.4 <br />WSE will then run the model for the 100-year flood event and one other flood event determined <br />through coordination with the Tech Team. Model results will be presented to the Tech Team in Task 2.1 <br />to assess the level of accuracy, identify primary flow paths, and compare to the results of stormwater <br />modeling completed in Task 2.4. WSE will complete additional model refinements, if necessary, based <br />on stakeholder input. <br />WSE willcreate a topographic workmap of the resulting 100-year inundation mapping and develop a <br />brief technical memo to document the model updates. <br />Assumptions: <br />. Modeling will be completed by updating Whiskey-Mercer HEC-RAS 2D model that was most <br />recently updated in 2023. <br />Deliverables: <br />o Updated HEC-RAS model that complies with FEMA guidelines and specifications for flood risk <br />assessment and mapping. <br />o A topographic workmap showing draft 100-year inundation extents based on most current <br />FEMA methods as determined in Task 2.3. <br />o Brief technical memo documenting model updates