AESI completed hydraulic analysis and floodplain mapping for 28.9 miles of the Beaverhead River and 54.5 miles of the Ruby River in Madison County, Montana. AESI worked closely with the Montana Department of Natural Resources and Conservation, the Federal Emergency Management Agency (FEMA), and FEMA contractors to complete the study in compliance with federal and state standards. The work completed by AESI is the basis for the Flood Insurance Study and the Flood Insurance Rate Maps for these two rivers in Madison County.
Hydraulic modeling was completed with HEC-RAS, and floodplain mapping was completed using ArcMap. The study reach was complicated by numerous bridges and culverts and a complex network of split flows. The study reaches included wide river valleys with numerous abandoned channel reaches and sloughs that convey flow during large flooding events. In total, over 71 miles of secondary flooding sources (i.e. split flows) were modeled. Due to these complexities, AESI created a rough 2D model in HEC-RAS to help guide cross-section layout in the regulatory 1D HEC-RAS hydraulic model. In total, the models contained 154 miles of stream reach, 1,853 cross-sections, and 36 hydraulic structures (bridges or culverts).