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Henry’s Lake Outlet: Flow and Sediment Assessment Sagar Neupane University of Idaho and Erika Ottenbreit, Helalur Rashid, and Joe Wagenbrenner Washington.

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Presentation on theme: "Henry’s Lake Outlet: Flow and Sediment Assessment Sagar Neupane University of Idaho and Erika Ottenbreit, Helalur Rashid, and Joe Wagenbrenner Washington."— Presentation transcript:

1 Henry’s Lake Outlet: Flow and Sediment Assessment Sagar Neupane University of Idaho and Erika Ottenbreit, Helalur Rashid, and Joe Wagenbrenner Washington State University with Peter Goodwin, Ph.D. University of Idaho and Dave Tuthill, Ph.D. Idaho Water Engineering

2 Why Are We Here?  You are interested in the Outlet and the Henry’s Fork Watershed  We want to provide an independent, scientific, and computational assessment  We all want to move toward a common goal

3 Outline  Background  Brief history  Stream processes and concepts  Project description and results  Some conceptual alternatives

4 Problem Statement  Sedimentation observed downstream  Erosion in the straightened channel  Restoration project restored flow to meandering channel  Challenged the historically strong communication and cooperation among the parties  Capacity of restored reach did not meet agreed minimum (300 cfs)

5 Background: History  1920’s:  0.5 mile straightened channel created  natural channel abandoned  1990’s  The Outlet was a source of downstream sediment  (Stumph 1995, Wesche 1997, HabiTech 1997)

6 Background: History (Cont.)  Sedimentation reduced quality of water and aquatic habitat  The Henry’s Fork Foundation and the Flat Rock Club assessed the upper Henry’s Fork reaches

7 Background: History (Cont.)  Specialists consulted:  Restoration of the natural channel would reduce sedimentation (Jock Conyngham, Jim Gregory, Rob Van Kirk, and Boyd Burnett)  Restoration ground work started in 2004  Fremont Madison Irrigation District and North Fork Reservoir Company protested in 2005  MOU established in 2006

8 Background: History (Cont.)  Directed flow to the abandoned meandering channel (2007) (restored channel)  Tests by USGS (2008) showed:  Restored channel could not meet the agreed MOU flow (300 cfs)  Overbank flow occurred at around 180 cfs

9 Background: Our Involvement  FMID and NFRC consulted with Idaho Water Engineering  The parties saw the benefit of an independent assessment  Class project established

10 Background: Stream Processes  Sediment and transport in channels  Channel stabilization and equilibrium  Natural flooding processes  Riparian habitat Photo courtesy of Dell Raybould

11 Sources of Sediment Sources include  Bed  Banks  Tributaries and hillslopes Bank Instability Photo courtesy of Dell Raybould

12  Bedload  Larger particles  “Bounce” along bed  Suspended load  Smaller particles  Transported in the water column Channel incision Vertical banks Types of Sediment Transport Photo courtesy of Dell Raybould

13 Dynamic equilibrium:  Balance and  Constant change Channel Stabilization and Equilibrium (FISRWG, 1998 Rosgen,1966 from Lane,1955) SedimentFlow = deposition incision

14 NLWRA 2002 Interface between land and aquatic ecosystem Effects of floods Channelization and changes Riparian and Stream Processes

15 Riparian and Stream Processes (Cont.) FISRWG, 1998

16 “Bankfull” Description Mean Annual Flow Bankfull Flow Low Flow Bankfull Flow 100 Year Flood

17 Effective Discharge Frequency Sediment Effective Discharge Discharge Low Flow Effective Discharge 100 Year Flood Sediment transport Work on channel Most common discharge

18 Effective vs. Bankfull: 3 cases a) Effective discharge = bankfull discharge Erosion and sediment transport potential balanced b) Effective discharge < bankfull discharge Too much work on channel Incision and bank erosion occur c) Effective discharge > bankfull discharge Not enough work on channel Deposition and channel widening occur Goodwin, 2004

19 Common Restoration Approaches  Address sources of sediment  Stabilize banks and bed  Install vegetation, armoring, or structures  Address upland and upstream sources of sediment  Reestablish connection to floodplain  Rejuvenate vegetation  Reintroduce natural flow regimes  Timing and duration of high and low flows  High and low flows impact stream processes

20 Questions So Far? Photo courtesy of Dell Raybould

21 Project Objectives  Evaluate the physical attributes of the two channels  Determine channel discharge capacity  Calculate sediment transport rates  Estimate the timing of overbank flows  Propose a range of alternatives  Support collaboration among interested parties

22 Stakeholders’ Needs Common Needs Equal benefit solution Reduce sedimentation Landowners Minimize flooding Reduce bank erosion (and loss of pasture) Maintain Lake level HFF and TNC Improve habitat FMID and NFRC Control over quantity and timing of flows

23 Working Constraints  180 cfs is bankfull flow in restored channel  Existing data (USGS, Wesche and Wesche, Gregory, Van Kirk and Burnett, and Conyngham)  Common methods

24 Solution Approaches  Channel capacity: Manning’s equation  Sediment transport: four different equations  Compared existing and non-vegetated scenarios  Flood analysis  Historic records (USGS)  Reconstructed, unregulated flow records (Van Kirk and Burnett)  Effective discharge

25 From Gregory, 2009 Slope=0.11% Slope=0.054%

26 Bankfull flow (cfs) Existing condition Non-vegetated scenario Straightened channel310 ( )670 ( ) Restored channel180 (NA)270 ( ) Results: Channel Capacity Low Flow Bankfull Flow 100 Year Flood

27 Results: Sediment Transport Potential Sediment transport * (ton/day) Existing condition Non-vegetated condition Straightened channel at bankfull (307 cfs) Straightened channel at 180 cfs Restored channel at bankfull (180 cfs) *Assumes sediment is available for transport

28 Measured Sediment Load  Wesche and Wesche (1996) estimated the sediment load to be tons/day at 150 cfs  In range of estimated transport potential for the straightened channel  Greater than the estimated sediment transport potential for the restored channel  Much higher sediment transport potential at higher flows

29 Days of Overbank Flow Overbank flows:  Provide nutrients and sediment to riparian area  Help mitigate spread of upland or invasive vegetation  Can be problematic for grazing management

30 Results: Overbank Flow Mean Annual Flow Historic: 57 cfs ( 114 days) Unregulated: 66 cfs ( 99 days) Bankfull Flow

31 Results: Years with flow >180 cfs

32 Results: Days with flow > 180 cfs

33 Results: Effective Discharge Historic (cfs) Unregulated (cfs) Straightened channel120 (80-220)70 (60-150) Restored channel170 (20-220)120 (70-260) Straightened Restored

34 Results: Summary  Flow capacity greater in straightened channel than restored channel  Sediment transport potential greater in straightened channel than restored channel  No-vegetation scenario would increase capacity, sediment transport, and channel instability  Restored channel  Probably will not convey 300 cfs  Overbank flows would occur 29 days/year without regulation

35 Questions So Far? Photo courtesy of Dell Raybould

36 Conceptual Alternatives: Perspective  Henry’s Fork watershed  Famous recreation  Population pressures  Reasons you may depend on the Outlet  Livelihood  Your living environment (society, recreation, etc.)  Other challenges:  2010 will be a dry year  Climate change will affect the watershed  Collaboration better than conflict

37 Conceptual Alternatives: Considerations  Increase flexibility in irrigation deliveries  Restore natural sediment transport regime  Establish a more natural flow regime to enhance stream function  Eliminate flooding when it would not naturally occur  Maintain lake levels during recreation periods  Enhance the fishery  Enhance function and aesthetic appeal by recovering native vegetation

38 Conceptual Alternatives  Return flow to straightened channel  Install check dams or other sediment traps  Protect banks with vegetation, rocks, or material

39 Conceptual Alternatives (Cont.)  Restored channel only  Allow straightened channel to return to meadow  Channel work: remove vegetation or sediment? Add bank protection?  Or combined approach…

40 Conceptual Alternatives (Cont.)  Dual channels  Add a device to control flows between the two channels  Enhance natural condition of restored channel  May provide for habitat improvements but needs further evaluation  Will provide conveyance needs  An equal benefits solution?

41 Conceptual Alternative: Dual Channels  Natural hydrograph for the restored channel  Extra conveyance in straightened channel  Control structure could be designed for least impact to fish and sediment routing control  Straightened channel could function as a back channel or oxbow lake; could also be designed to sediment-in over time  Maintenance might be needed in straightened channel during offline periods

42 Conceptual Alternatives (Cont.) Other thoughts  Alter the timing of releases from Henry’s Lake  Maintain volume of conveyance through the Outlet  Convey at lower rates  longer flow periods  Lake level constraints?  Provide higher flows in the spring to provide a more natural hydrologic cycle  Use alternative irrigation sources or storage (downstream or offline)

43 Acknowledgements: Fremont Madison Irrigation District North Fork Reservoir Company The Nature Conservancy Henry’s Fork Foundation Jim Gregory, Rob Van Kirk, Dell Raybould and Kresta Davis-Butts, Laura Garcia, Travis Lopes, and Colt Shelton Thanks for your attention!! Photo courtesy of Dell Raybould

44 Possible Future Actions  Additional monitoring  Sediment size and quantity  Channel shape change  Further analysis  Estimate equilibrium channel shape  Flooding of adjacent land  Model different alternatives  Identify equal benefit solutions


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