Draft Final Report Virgin River Master Plan A road map for reconstruction, management, and long-term maintenance Virgin River Washington County, Utah Revised July 2007 Natural Channel Design, Inc. 3410 S. Cocopah Drive Flagstaff, AZ 86001 Virgin River Master Plan Draft Final Report Washington County, Utah Revised: July 2007 TABLE OF CONTENTS Table of Contents ............................................................................................................................. i List of Figures.............................................................................................................................. ii List of Tables.............................................................................................................................. iii Section 1: Introduction .................................................................................................................... 1 Project Description/Objectives.................................................................................................... 1 SW Utah Flood Flows ................................................................................................................. 2 Study Approach........................................................................................................................... 3 Methods....................................................................................................................................... 4 Master Plan Components............................................................................................................. 4 Study Philosophy......................................................................................................................... 5 A Note About Stream Stability.................................................................................................... 5 Frequently Asked Questions........................................................................................................ 6 Regulatory Permitting ................................................................................................................. 7 Section 2: Project Description......................................................................................................... 1 Project Area................................................................................................................................. 1 Basin Description ........................................................................................................................ 2 Project Reaches ........................................................................................................................... 2 Hydrology.................................................................................................................................... 3 Section 3: Stream Channel Stability Analysis................................................................................. 6 Stream Channel Processes........................................................................................................... 6 Mechanisms of Channel Change ............................................................................................... 12 Geomorphic Assessments..........................................................................................................13 Hydraulic Analysis .................................................................................................................... 22 Conclusions ............................................................................................................................... 24 Section 4: Stream Stability Template ............................................................................................26 Guiding Stability Principles ...................................................................................................... 26 Riparian Corridor Zones............................................................................................................ 30 Channel Realignment ................................................................................................................ 32 Channel Cross-section Template............................................................................................... 32 Revegetation Strategies ............................................................................................................. 35 Appropriate land uses................................................................................................................ 38 Channel Capacity Excavation.................................................................................................... 39 Exotic Plant Species Removal & Re-vegetation ....................................................................... 42 Controlling Overbank Flow.......................................................................................................46 Bank Stabilization Measures .....................................................................................................48 Nuisance and Stormwater Flows ............................................................................................... 50 Wetlands and Water Quality ..................................................................................................... 50 Long-term Riparian Corridor Monitoring/Maintenance............................................................ 52 Transportation Corridors ........................................................................................................... 53 Trails, Parks, and Open Space...................................................................................................53 Native Plant Nurseries............................................................................................................... 54 Public Outreach and Education ................................................................................................. 55 Section 5: Reach Recommendations/maps.................................................................................... 56 Reach 1 ...................................................................................................................................... 57 Reach 3 ...................................................................................................................................... 61 Reach 4 ...................................................................................................................................... 63 Reach 5 ...................................................................................................................................... 65 Reach 6 ...................................................................................................................................... 67 Reach 7 ...................................................................................................................................... 69 i Virgin River Master Plan Draft Final Report Washington County, Utah Revised: July 2007 Section 6: References .................................................................................................................... 72 APPENDIX A. Bank Stabilization Strategies .............................................................................. 74 Bioengineering Practices ........................................................................................................... 74 Structural Measures................................................................................................................... 78 List of Figures Figure 1 Reconstruction of January 2005 flood flows. (Cram, WCWCD) ..................................... 2 Figure 2 Map of Project Area: Virgin River.................................................................................... 1 Figure 3 Virgin River Peak Flows at Virgin and Hurricane, UT stream gage stations ................... 4 Figure 4 Typical Virgin River meander upstream of project area................................................... 8 Figure 5. Natural vs. “Designed” Channels..................................................................................... 9 Figure 6 Channel meander and adjustments.................................................................................. 10 Figure 7 Riparian Planting Zones.................................................................................................. 11 Figure 8 Channel, floodplain, terrace features. ............................................................................. 15 Figure 9 Meander Pattern Parameters. .......................................................................................... 18 Figure 10 Reach 1 meander pattern measurements. ...................................................................... 19 Figure 11 Reach 5 meander pattern measurements. ...................................................................... 19 Figure 12 Design Cross-section Template..................................................................................... 25 Figure 13 Appropriate channel/floodplain elevations ................................................................... 27 Figure 14 Incorrect channel/floodplain elevations ........................................................................ 27 Figure 15 Appropriate overbank roughness. ................................................................................. 28 Figure 16 Incorrect overbank roughness. .....................................................................................