Resolution 2024-084 - Laserfiche WebLink

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1+WATERSHED SCIENCE & ENGINEERING April30,2024 information about the City's stormwater system, roads, bridges, culverts, watercourse data, ground elevations, changes in the terrain, records of flooding, and climate change predictions. Perteet will prepare a City Conditions Memo that describes the current conditions in the City and the data collection process, provides an inventory of data collected and its quality, and identifies the system or capacity needs within Ellensburg to support future mitigation strategy development. The memo will also identify recommendations for additional data collection and discuss any assumptions that were made about the collected data or its use. The following tasks will be completed by WSE: o Review the collected data that pertains to surface water flooding. o Participate in a one-day field investigation to support data collection. r Provide input on surface water flooding issues for the City Conditions Memo. Assumptions: o Two WSE staff will participate in a one-day field investigation to verify existing data and/or collect additional data. Deliverables: r WSE contributions to the draft and final City Conditions Memo Tosk 2.3. Floodplain Analysis The consultant team and Tech Team will review the current draft flood maps and compare extents to photos or accounts of past flooding events. Perteet will gather information about past flooding events to develop a greater understanding of flood dynamics and what influences flow paths through the City. Depending on the availability, completeness, and level of confidence of the flow paths and past flooding data, Perteet may map past event flood extents in GIS and prepare a flood history map. The consultant team will identify where there have been changes to the built environment that may affect flood flows since the most recent LiDAR was collected in 2019 (e.g. new road cuts through the Cascades to Palouse trail embankment, new curbs, or other changes the terrain). This may include meetings with City maintenance staff to better understand the performance of the existing stormwater system or past flooding. The results of the data collection, summary of flood dynamics, and effects of climate change will be included in the Task 2.2 Cily Conditions Memo. The following tasks will be completed by WSE: o Review background data and mapping and contribute to the review and comparison of past flooding to the current flood model results. o Coordinate with FEMA to discuss methods of identifying flow paths in urban alluvial fans (e.g. method used to map Wenatchee Number 2 Canyon) and when Zone X should be used for areas with very shallow flooding. The consultant team will analyze how the selected climate change scenario will affect the City. o Provide input on past flooding comparison to existing hydraulic model results for Task 2.2 City Conditions Memo