2021-01-11-minutes-public-works-study-session

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Dept. of Public Works Page 2 BACKGROUND The Kittitas County Flood Control Zone District (FCZD) received funding from the Federal Emergency Management Agency (FEMA) to conduct a Crystal Creek Flood Study and to update the official maps used by FEMA and community officials based on the outcomes of the new study. Crystal Creek was chosen for the flood study based on local community interest and the desire for the FCZD to begin remapping priority watershed in Upper Kittitas County. FEMA -funded flood studies and remapping efforts must conform to FEMA standards. Studies can be either detailed or approximate. In approximate areas, the 100 -year floodplain is identified but the study does not establish base -flood elevations or identify the floodway. National Flood Insurance Program (NFIP) communities are required to regulate development within these 100 - year floodplain but have little information about these areas. Detailed studies not only identify the footprint of the 100 -year floodplain, but also identify base -flood elevations, 500 -year floodplains, and floodways. Floodways have very high regulatory standards, including a prohibition on new residential structures. 500 -year floodplains have no minimum regulatory requirements, though communities can choose to regulate these areas. FEMA is in the process of updating the FEMA floodplain maps throughout the County. This effort did not include any new studies for Crystal Creek, and differences between the "old" 1981 maps and "New" maps anticipated in 2021 for the Crystal Creek floodplain are due to more accurate topography data available from the 2011 LiDAR flight. DISCUSSION: The results of the Crystal Creek flood study did not result in the expansion of the floodway and in many places resulted in a reduction of the footprint of the 100 -year floodplain. There is a section within unincorporated Kittitas County, just downsteam of Roslyn, where more detailed modeling indicated that an expansion of the 100 -year floodplain is necessary. Newly constructed and significantly improved buildings within a FEMA -mapped 100 -year floodplain must be built to heightened building standards that address flood risk. Previously, an approximate study was used to map Crystal Creek upstream of No. 5 Mines Rd. The new modeling extended the detailed modeling the entire mapped length of Crystal Creek. Detailed modeling identifies base flood elevations, which allows for development requirements to be tailored to flood risk of the site. In the absence of a base flood elevation, a uniform requirement of building the first floor of a home two feet above highest adjacent grade must be applied. Flood insurance rates for new homes are also lower when a base flood elevation is available. The Kittitas County Flood Control District conducts outreach aimed at informing residents about upcoming map changes. The FCZD proposes sending out notices to any landowners impacted by mapping changes and coordinating with the Cities of Cle Elum and Roslyn in outreach efforts.. 411 N. Ruby St., Suite #1 TEL (509) 962-7523 Ellensburg, WA 98926 FAX (509) 962-7663