04-04-2016 Council Packet - Laserfiche WebLink

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WSB reviewed the data that was provided to FEMA during the map update process. The City provided topographic information and Letter of Map Revisions to the FEMA contractors. The City also requested that Rice Creek Watershed District submit their technical modeling on the City’s behalf. Rice Creek Watershed District provided FEMA with a lake level frequency analysis for the Chain of Lakes, hydrologic and hydraulic modeling for Clearwater Creek, Hardwood Creek, Rice Creek, and Anoka County Ditches 10-22-32, 15, 25, 31 and 46. For the lake level frequency analysis, RCWD reviewed all available gage records on the lakes and interpolated the 100-year flood elevation for each lake. For the modeling, RCWD reviewed both the 100-year 24-hour storm and the 100-year 10 -day storm, which simulates flooding caused by spring snowmelt. The higher of the two 100-year events was used to establish the 100-year floodplain elevation and extents. The result of the RCWD studies is that the 100-year flood elevations on the Chain of Lakes increased due to the longer gage record available since 1981. FEMA uniformly accepted RCWD’s data for the Chain of Lakes, Rice Creek, ACD 15 and 10-22-32. FEMA accepted portions of the ACD 25, Clearwater Creek and Hardwood Creek studies. Areas with approximate Zone A were essentially left unchanged. Revising the Effective Maps After the maps have been adopted and published, there are a few options for communities to contest the final mapping. The first option would be to authorize a City-wide independent detailed study to determine the floodplain elevations and extents. This is an expensive option and does not guarantee that the results would be any different than the 2015 maps. A second option would be to revise the approximate Zone A areas and establish flood elevations for these areas for future reference and existing homeowners’ benefit. Areas under development are already required to establish a base flood elevation as part of the development review. A third option would be to enter into the Community Rating System which would allow the City to provide discounted rates on flood insurance to its residents. WSB & Associates staff will be in attendance at the work session to answer questions. Requested Council Direction None required. Information only. Attachments 1. 1982 Flood Insurance Rate Map 2. 2015 Flood Insurance Rate Map 3. 2015 Digital Data 4. Changes Since Last FIRM 5. Example of Structures Affected by Floodplain at Reshanau Lake