Henry's Lake Outlet Presentation - Idaho Water Engineering

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22 févr. 2014 (il y a 3 années et 6 mois)

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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 State University


with


Peter Goodwin, Ph.D.

University of Idaho

and


Dave Tuthill, Ph.D.

Idaho Water Engineering

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

Outline


Background


Brief history


Stream processes and concepts



Project description and results



Some conceptual alternatives

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)




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)

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


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

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


Background: Our Involvement


FMID and NFRC consulted with Idaho Water
Engineering



The parties saw the benefit of an independent
assessment



Class project established


Background: Stream Processes


Sediment and transport in channels



Channel stabilization and equilibrium



Natural flooding processes



Riparian habitat


Photo courtesy of Dell Raybould

Sources of Sediment

Sources include


Bed


Banks


Tributaries and hillslopes


Bank
Instability


Photo courtesy of Dell Raybould


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

Dynamic equilibrium:


Balance and


Constant change


Channel Stabilization and Equilibrium

(FISRWG, 1998

Rosgen ,1966 from Lane ,1955)

Sediment

Flow

=

NLWRA
2002

Interface
between land
and aquatic
ecosystem


Effects of floods


Channelization
and changes

Riparian and Stream Processes

Riparian and Stream Processes (Cont.)

FISRWG, 1998

“Bankfull” Description

Mean Annual Flow

Bankfull

Flow

Low Flow

Bankfull Flow

100 Year Flood

Effective Discharge

Frequency

Effective Discharge

Discharge

Low Flow

Effective Discharge

100 Year Flood

Sediment transport

Work on channel

Most common
discharge

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

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

Questions So Far?

Photo courtesy of Dell Raybould

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



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

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

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

From Gregory, 2009

Bankfull

flow

(
cfs
)



Existing
condition

Non
-
vegetated
scenario

Straightened channel

310 (290
-
320)

670 (645
-
678)

Restored channel

180 (NA)

270 (230
-
353)

Results: Channel Capacity

Low Flow

Bankfull Flow

100 Year Flood

Results: Sediment Transport Potential

Sediment

transport * (ton/day)

Existing
condition

Non
-
vegetated

condition

Straightened

channel

at
bankfull

(307
cfs
)

130
-
220

210
-
630

Straightened

channel

at 180
cfs

0
-
100

30
-
80

Restored channel

at

bankfull

(180
cfs
)

1
-
3

3
-
50

*Assumes sediment is available for transport

Measured Sediment Load


Wesche and Wesche (1996) estimated the
sediment load to be 14
-
21 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

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

Results: Overbank Flow

Mean Annual Flow


Historic: 57
cfs

( 114 days)

Unregulated: 66
cfs

( 99 days)

Bankfull

Flow

Historic record

Unregulated record

%

Equaled
exceeded

Days

overbank

%

Equaled
exceeded

Days

overbank

Straightened channel

(307
cfs
)

2

5

<0.1

<1

Restored channel

(180
cfs
)

8

29

4.5

16

Results:
Years with flow >180
cfs

0
20
40
60
80
100
# days with flow > 180 cfs
Historic
Unregulated
0
2
4
6
8
10
12
14
days > 180 cfs
Historic
Unregulated
Results:
Days with flow > 180
cfs

Results: Effective Discharge

Historic


(
cfs
)

Unregulated

(
cfs
)

Straightened channel

120 (80
-
220)

70 (60
-
150)

Restored channel

170 (20
-
220)

120 (70
-
260)

Straightened

Restored

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


Questions So Far?

Photo courtesy of Dell Raybould

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


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


Conceptual Alternatives


Return flow to straightened channel


Install check dams or other sediment traps


Protect banks with vegetation, rocks, or material




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…

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?

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

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)



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

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