Proposed Floodplain Inundation Mapping on the Flathead River

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

Completed Work § Columbia River Treaty Study effort 2009 -2014 ► ► ► Extensive Li. DAR 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 BUILDING STRONG®

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

Revisions Proposed § Identify FIM reach of interest ► ► Columbia Falls reach or lake backwater reach? Meet NWS/USGS requirements for FIM § Convert overbank areas to 2 D ► RAS 5. 0 for complex flooding in backwater reach § Operations ► ► Revise hydrology inputs Define Kerr operation scenarios BUILDING STRONG®

BUILDING STRONG®

BUILDING STRONG®

Products § Updated 1 D-2 D 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 BUILDING STRONG®