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

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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 P'EMA 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 resulted in no large changes in our understanding of flood risk or extent within the City of Cle Elum. In downtown Cle Elum, the hydraulic modeling indicates that during the 100 -year flood, Crystal Creek floods overbank north of 2"d Street and continues east as shallow flooding with less than 1 foot of depth. This flooding was also identified in the work maps associated with the 1981 FEMA maps. Since the 1981 FEMA maps identify these areas as Zone B (areas with between a 1% and 0.2% annual change each year), in the LOMR we propose to maintain the same flood designation. This designation, which is also referred to as the 500 -year floodplain, would not create a mandatory flood insurance requirement, but the City of Cle Elum could consider utilizing this flood study for stormwater planning and project implementation. Since there is risk of shallow flooding, even during the 100 -year flood event, the City of Cle Elum consider applying higher building standards within this area identified as a 100 - year floodplain. 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 City of Cle Elum so that both FCZD staff and Cle Elum staff are listed as contacts on outreach materials to landowners within the City of Cle Elum. FISCAL IMPACTS: The Crystal Creek flood study and remapping effort was largely supported through FEMA funding. The Flood Control Zone District has included outreach, including staff time and required materials) in is 2021 budget. Page 2 of 9 PUBLIC WORKS BOARD OF COUNTY COMMISSIONERS WORK SESSION STAFF REPORT