03252024_PublicWorksStudySession_Briefings

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KITTITAS COUNTY DEPARTMENT OF PUBLIC WORKS PUBLIC WORKS—BOARD OF COUNTY COMMISSIONERS STUDY SESSION STAFF REPORT STUDY SESSION DATE: March 25,2024 TOPIC: Letter from FEMA Dated March 13, 2024 ACTION REQUESTED: Direction to Staff LEAD STAFF: Arden Thomas RECOMMENDATION: Direct staff to continue to support FEMA's efforts to improve flood risk models and update the Board of County Commissioners about the status of the investigation. BRIEFING SUMMARY: • The Board of County Commissioners received a letter from the Federal Emergency Management Agency (FEMA) regarding a proposed flood risk study. • The proposed flood risk assessment methodologies use techniques vetted by the Flood Control Zone District. • The areas selected by FEMA for study are locations where County staff have concerns that current FEMA mapping does a poor job assessing flood risk. • The FEMA study includes an area located just east of Cle Elum, and several streams on the east end side of the Kittitas Valley. • There will be opportunities through the FEMA process to provide feedback and comment. BACKGROUND: Many of the mapped floodplains within Kittitas County were assessed for flood risk in the late 1970s and developed utilizing approximate mapping techniques. The Flood Control Zone District has been securing FEMA funding to update maps. FEMA now proposes to conduct flood studies for several streams on the east side of the Kittitas Valley and for an area east of Cle Elum. These studies would eventually update the regulatory maps. DISCUSSION: The current mapping is based on outdated information and engineering methods. The Flood Control Zone District has been utilizing 2-D modeling to assess flood risk along alluvial fans,which is the best model approach for complicated out of bank flooding. FEMA will be utilizing this modeling approach where appropriate. Page 1 of 3 PUBLIC WORKS BOARD OF COUNTY COMMISSIONERS WORK SESSION STAFF REPORT i I