On January 14th an appeal to the Preliminary Davis County Insurance Study was submitted to FEMA. Layton City staff worked in conjunction with our consultant, Bowen Collins & Associates to review the study performed by FEMA's consultant. The major components of the appeal are the incorrect hydrology, lack of detention basins and model inaccuracies. The proposed model storm produced runoff flows significantly higher than the previous studies, some up to 3 times the flows.
The distribution of rainfall over a short time period based on a national model was used to produce the Preliminary maps. In contrast, when a local storm distribution is used, the runoff flows are more similar to the historic flows. The runoff is also reduced by adding the existing detention basins to the computer model to mimic actual storm conditions. During the course of reviewing the measurements and data used in the computer modeling, some errors were also found and a table with these discrepancies were submitted to FEMA.
During the past several weeks, Layton City has participated in coordinating meetings and phone conferences with other Cities in Davis County, Davis County Flood Control, FEMA consultants and representatives from FEMA and the State of Utah. This collective effort has provided valuable information to the consultant and the results were a comprehensive appeal, not only from Layton City, but for entire Davis County relating to the floodplain studies.
Layton City has also updated existing geographical contours and elevations along the channels with the use of LiDAR (Light Detection and Ranging) survey to improve the accuracy of the stream banks. This will be incorporated into the delineation of the new floodplain.
We anticipate the appeal process to take several months and will post comments to our web site to keep the public appraised of the latest status of the Appeal Process. If you have any further questions, please contact the Public Works Engineering Department at (801) 336-3700.