*Updates to the orginal Ruby CMZ were made in 2017 as part of the Clear Creek CMZ. Final Report Please also see the Clear Creek CMZ Report and the Upper Missouri Headwaters CMZ Summary Report. November 30, 2010* Ruby River Channel Migration Zone Mapping Karin Boyd, PG Applied Geomorphology, Inc. Prepared for: 211 N Grand Ave, Suite C Bozeman, MT 59715 Ruby Valley Conservation District 406‐587‐6352 P.O. Box 295 Sheridan, MT 59749 Tony Thatcher & Bryan Swindell DTM Consulting, Inc. 211 N Grand Ave, Suite J Bozeman, MT 59715 406‐585‐5322 Table of Contents 1.0 Introduction ............................................................................................................. 1 1.1 Channel Migration and Avulsion Processes ......................................................... 1 1.2 The Channel Migration Zone Mapping Concept ................................................. 7 1.3 Uncertainty ........................................................................................................... 8 1.4 Relative Levels of Risk ........................................................................................ 9 1.5 Potential Applications .......................................................................................... 9 1.6 Disclaimer and Limitations ................................................................................ 10 1.7 Acknowledgements ............................................................................................ 10 2.0 Physical Setting ..................................................................................................... 13 2.1 Geology .............................................................................................................. 15 2.2 Geomorphology .................................................................................................. 17 2.3 Hydrology........................................................................................................... 19 2.3.1 Mean Daily Flows ....................................................................................... 19 2.3.2 Flood History .............................................................................................. 20 2.4 The 1994 “Sediment Event” ............................................................................... 21 3.0 Methods................................................................................................................. 23 3.1 Imagery ............................................................................................................... 23 3.2 GIS Project ......................................................................................................... 24 3.3 Banklines ............................................................................................................ 24 3.4 Project Reaches .................................................................................................. 25 3.4.1 Reach 1........................................................................................................ 27 3.4.2 Reach 2........................................................................................................ 27 3.4.3 Reach 3........................................................................................................ 27 3.4.4 Reach 4........................................................................................................ 27 3.4.5 Reach 5........................................................................................................ 27 3.4.6 Reach 6........................................................................................................ 28 3.4.7 Reach 7........................................................................................................ 28 3.5 Migration Rate Measurements ........................................................................... 28 3.6 Bank Armor Extents ........................................................................................... 28 3.7 Inundation Modeling .......................................................................................... 28 4.0 Results ................................................................................................................... 31 4.1 The Historic Migration Zone (HMZ) ................................................................. 31 4.2 The Erosion Hazard Area (EHA) ....................................................................... 32 4.2.1 Data Stratification ....................................................................................... 35 4.2.2 Outliers ........................................................................................................ 36 4.2.3 Reach 5 Buffer ............................................................................................ 36 Ruby River CMZ FINAL i AGI and DTM 4.2.4 Buffer Performance ..................................................................................... 36 4.2.5 Geologic Controls on Migration Rate ......................................................... 38 4.3 The Avulsion Hazard Zone (AHZ) .................................................................... 38 4.4 The Restricted Migration Area (RMA) .............................................................. 42 4.5 The Restricted Avulsion Hazard Zone ............................................................... 42 4.6 Composite Map .................................................................................................. 44 4.7 Deliverables ........................................................................................................ 45 5.0 Recommendations ................................................................................................. 47 5.1 Individual Site Assessment using Existing Information .................................... 47 5.2 Incorporation of 1970s Imagery ......................................................................... 47 5.3 Additional Analysis to Support Individual Site Assessment ............................. 48 5.4 Incorporation of a Bank Armor Inventory ......................................................... 48 5.5 Short-Term CMZ Boundaries ............................................................................ 49 5.6 Jurisdictional Boundaries ................................................................................... 49 5.7 Investigate Lower River Avulsion ..................................................................... 49 6.0 References ............................................................................................................. 51 7.0 Appendix A: Mapped Erosion Sites, Ruby River ................................................. 53 8.0 Appendix B: Migration Rate Measurements ........................................................ 61 9.0 Appendix C: GIS Datasets .................................................................................... 69 List of Figures Figure 1. Bar formation, wood recruitment, and riparian vegetation succession, Ruby River. ........................................................................................................................... 2 Figure 2. Schematic drawing showing the meandering river migration concept (www.berkeley.edu). ................................................................................................... 2 Figure 3. Active bank erosion and channel migration, Ruby River (Spring, 2010). ......... 3 Figure 4. Schematic diagram of meander cutoff (www.uwsp.edu). .................................. 3 Figure 5. Example of the avulsion process, East Gallatin River May 2008 (DNRC). ...... 4 Figure 6. Example of two avulsions that occurred between 1955 and 1995 (yellow arrows). ....................................................................................................................... 5 Figure 7. Spring 2010 overbank flows creating avulsion hazard on Ruby River (S. Gillilan). ...................................................................................................................... 5 Figure 8. General Land Office Survey map of lowermost Ruby Valley showing river course as mapped in 1870 (green) and 2009 (blue). ................................................... 6 Figure 9. 1955 aerial image of Ruby River just downstream from Lewis Lane showing NHD line (blue) and 1955 channel course (pink); note ground disturbance near RM 7................................................................................................................................... 7 Figure 10. Ruby River Watershed (MTDEQ, 2006)........................................................ 13 Ruby River CMZ FINAL ii AGI and DTM Figure 11. Ruby River canyon section below Ruby Reservoir. ....................................... 14 Figure 12. Unconfined floodplain of the Ruby River Valley. ......................................... 14 Figure 13. Geologic map of the Ruby Valley; note extent of alluvial fans (Qf) and Bozeman Formation (Tbz) (Ruppel and others, 1993). ............................................ 16 Figure 14. Geologic map of the project reach (outlined in blue) showing alluvial fan extents (orange) in Ruby Valley (Van Gosen, et al, 1998). ..................................... 17 Figure 15. Lower Ruby River showing low floodplain and lack of coarse bar features. 18 Figure 16. Results of Ruby River inventory (Alvin, 1998) showing observed locations of unvegetated gravel bars (yellow). ............................................................................