1. US Army Corps of Engineers BUILDING STRONG ® Proposed Floodplain Inundation Mapping on the Flathead River Travis Ball Hydraulic Engineer 206-764-3277 Travis.d.ball@usace.army.mil

2. BUILDING STRONG ®  Columbia River Treaty Study effort 2009-2014 ► Extensive LiDAR collection ► 1500 miles of hydraulic modeling ► 70 years of hydrology for all reaches (used synthetics if needed)  Reach 28: Hungry Horse Dam to Kerr Dam ► U/S boundary – HHG outflow. D/S boundary – Kerr forebay ► Includes Flathead Lake ► Unsteady with 7 levee systems ► Surveyed channel cross sections included ► Hydraulic modeling report ► Limited mapping for extreme events Completed Work

3. BUILDING STRONG ® LiDAR Boundary 3000 sq. miles 4 states 42 counties 180,000 structures 160 levee systems 1600 river miles 9 points per sq. meter

4. BUILDING STRONG ®  Identify FIM reach of interest ► Columbia Falls reach or lake backwater reach? ► Meet NWS/USGS requirements for FIM  Convert overbank areas to 2D ► RAS 5.0 for complex flooding in backwater reach  Operations ► Revise hydrology inputs ► Define Kerr operation scenarios Revisions Proposed

5. BUILDING STRONG ®

7.  Updated 1D-2D Unsteady hydraulic model ► Keeping the HHG-KER extents  Flood Inundation Mapping ► Library of inundation maps for selected sub-reach for range of flow scenarios  Report ► Technical hydraulic modeling report to function as user’s guide Products