Short course for UNIVERSIDAD NACIONAL DE INGENIERIA January 26-29, 2016 Planning and Design for Rehabilitation of Rivers Using Large Wood Metodología para Reforestar Ríos Degradados por Actividades Humanas usando Técnicas de Bioingeniería
2.0 Screening and selecting sites for using large wood
Course overview Day I (Jan 26)--Foundational topics
Introductions
Review of information resources (design handbooks and spreadsheets) for large wood
Is wood appropriate for your site?—criteria for screening (Planning)
Three design approaches
Key issues for large wood design
Day 2 (Jan 27)—Designing large wood structures
Case study I—Little Topashaw Creek, Mississippi
Design life for wood structures/selection of design event or condition
Types of wood structures
Findings of recent research on drag and lift coefficients
“Road testing” selected design spreadsheets
Day 3 (Jan 28)—Risk, uncertainty and construction
Sensitivity and Monte Carlo analyses
Constructability assessment
Case study II—Trinity River, California
Monitoring
Day 4 (Jan 29)--Field trip
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Screening sites for large wood It’s not for everybody
The last temptation is the greatest treason: to do the right deed for the wrong reason. --T. S. Eliot
So what does that have to do with large wood placement in rivers? Shields Engineering LLC
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What is the “right reason” for placing LW in rivers? Wood should be placed in and along rivers to accelerate recovery of natural processes. These processes should lead to a new state for the river system so that wood inputs and outputs/decay roughly balance. So what are the “natural processes” we are trying to recover?
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Wood before we changed things
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Natural processes for wood contribution to river channels Bank erosion Channel avulsion Severe weather, windthrow Landslides Debris flows Fires
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Historically elevated LW loads
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Natural channels retain lots of wood
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So, before we changed things… Lots more wood in channels Wood part of riverine landscape Much larger wood in channels
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Wood drifts, accumulates, builds new floodplain
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Stable natural wood in Queets River, WA
T.B. Abbe, D.R. Montgomery / Geomorphology 51 (2003) 81–107
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Really big trees Reported Wood Diameters, m
6
5
Eastern old growth forests
Snags pulled from rivers
4 3
Max, size m Min size,m
2 1 0 Nisqually River
Mississippi River
Red River
From large wood national manual
white pine
sycamores
tulip poplar
cottonwood and oak
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Why is watershed tree size so important to processes governing instream wood? Shields Engineering LLC
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Why is watershed tree size so important?
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The “floodplain-large wood cycle”
Pieces of wood large enough to resist transport stay around These “key members” initiate and stabilize wood formations These wood formations trigger sediment deposition, which creates “alluvial patches” (high bars or islands) Wood protects patches from erosion long enough for trees to start growing on the deposited sediment Stable patches can remain long enough for trees to become very large and mature…even 100s of years. More stable than surrounding floodplain Large trees are a future source of wood that restarts the cycle.... Collins, B. D. et al. (2012). Geomorphology, 139, 460-470. Shields Engineering LLC
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Pieces of wood large enough to resist transport stay around
Collins, B. D. et al. (2012). Geomorphology, 139, 460-470.
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These “key members� initiate and stabilize wood formations
Collins, B. D. et al. (2012). Geomorphology, 139, 460-470. Shields Engineering LLC
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Wood formations trigger sediment deposition, which creates “alluvial patches�
Collins, B. D. et al. (2012). Geomorphology, 139, 460-470. Shields Engineering LLC
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Wood protects patches from erosion long enough for trees to start growing on the deposited sediment
Collins, B. D. et al. (2012). Geomorphology, 139, 460-470. Shields Engineering LLC
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Stable patches can remain long enough for trees to become very large and mature‌even 100s of years. More stable than surrounding floodplain Collins, B. D. et al. (2012). Geomorphology, 139, 460-470. Shields Engineering LLC
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Large trees are a future source of wood that restarts the cycle....
Collins, B. D. et al. (2012). Geomorphology, 139, 460-470. Shields Engineering LLC
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Humans remove wood from rivers Directly by “snag removal” By modifying channels so that they are less retentive of debris
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Why are humans and LW so mutually exclusive? Luis F. Castro I.
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A vicious cycle Wood removal means less wood in the channel….the channel becomes smoother, straighter and simpler So it retains less drifting wood... So it has even less wood...new floodplains are not built and destroyed... So there is less wood added to the channel So it has even less wood
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Mining impacts
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So, when we remove wood… Change in area of active channel and forested islands, 1888–1998, in the North Fork Nooksack River, Washington, river kilometers 60–65
Forest was logged between 1918 and 1933.
Collins, B. D. et al. (2012). Geomorphology, 139, 460-470.
Changes in channel width and forested island frequency in the Cowlitz River, upstream of Packwood, Washington, river kilometers 205– 209
Forest was logged and wood was removed from river. Shields Engineering LLC
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Alternate “stable” states Hoh River(2009)
Higher complexity and diversity
Cowlitz River (2009) Lower complexity and diversity
1. Diversity of stable main and perennial secondary channel habitats 2. Abundant, high quality edge habitat 3. Fallen large trees entrained by river at eroding bank. 4. Stable jams at flow splits and secondary channel inlets 5. Deep scour pools associated with stable jams. 6. Forest age and species patch diversity, including mature conifer patches “hard points.”
Collins, B. D. et al. (2012). Geomorphology, 139, 460-470.
1. Braided, unstable main channel and shifting, ephemeral secondary channels. 2. Low quality of edge habitat 3. Riparian forest recruitment limited to small wood 4. Unstable pieces and accumulations of fluvial wood 5. Few, shallow pools 6. Low forest patch age and species diversity, dominantly ephemeral, young stands of pioneer tree species
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Collins, B. D. et al. (2012). Geomorphology, 139, 460-470.
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Reported contemporary loadings LW in N Miss Streams m2/km2 channel
See p. 1-27 to 1-28 in large wood national manual
before after
High Quality Low Quality LTC ds LTC
300,000
LTC ups Toby Tubby
0
20000 40000 60000 80000 100000
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LW as a restoration tool
What are stream ecosystems? ◦ In cross section from the thalweg to the point where channel related moisture no longer influences the plant community ◦ In the longitudinal direction, from the headwaters to watershed mouth
Note off-channel components of the system, especially riparian forests Shields Engineering LLC
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Process based restoration Beechie et al. 2010
Time
Landscape
Cause
Habitat
Biota Shields Engineering LLC
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Importance of riparian forests ď‚— ď‚—
How do forests influence the stream? How does the stream influence the forest?
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The constructed channel terminated abruptly!
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Fluvial response Upstream reaches incised via migration of headcuts
River Systems Morphology for Restoration Studies
June 20, 1997
Rechannelization in 2003
Thalweg profiles
Thalweg elevation, m NAVD88
June 20, 1997
1967 Channelization plans 1997 2003 Channelization plans 2004 2010
74 73 72 71 70
May 13, 2010
69 68 67 66 65 -5
0
5
10
Distance along channel upstream from debris plug origin, km
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Note interaction between wood and river! 2/10/1996
1/2/2007
9/18/2004
11/29/2012
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LW functions we hope to regain You’re on!…..?????
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So, obviously… Restoring the system requires…
“…land acquisition or conservation easements with aggressive riparian reforestation. …long-term stream restoration depends on understanding and accommodating processes at both the reach and watershed scale. Key to this is establishing a geomorphic response corridor that includes restoration of mature riparian forests and sufficient portions of the floodplain, channel migration zone and adjacent hillsides to accommodate fluvial processes and wood recruitment.” Roni et al. (2014a) point out that wood placement projects that did not take into account processes such as hydrology or sediment, tended to be the projects that did not show improvements [in biota].
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Restoration means‌.. 
Ecological restoration encompasses a set of intentional activities that initiates or accelerates the recovery of an ecosystem with respect to its health, integrity, and sustainability.
ď‚—
An ecosystem is considered restored when it contains sufficient biotic and abiotic resources to continue its development without further human assistance or intervention. It will sustain itself structurally and functionally, and will demonstrate resilience to normal ranges of environmental stress and disturbance. As a central component of these restoration activities, the use of wood plays a critical role in the restoration of fluvial aquatic ecosystems.
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Cardinal principles (Beechie et al. 2010)
Restoration actions should address the root causes of degradation. Restoration actions must be consistent with the physical and biological potential of the site. Restoration actions should be at a scale commensurate with environmental problems. Restoration actions should have clearly articulated expected outcomes for ecosystem functions. First, do no harm. Shields Engineering LLC
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Key questions for problem definition What are current problems with the ecosystem? Is there degradation of ◦ ◦ • ◦
Instream habitat (pools, cover, substrate conditions) Floodplain environment (immature forests, loss of wetlands) Water quality (excess fine sediment, Nutrients, high temperatures, pollution)
What are potential contributing factors? ◦ Has the flow been altered? (e.g., armored banks, levees, straightening, incision)? ◦ Is there point or non-point pollution? ◦ Has there been a loss of riparian vegetation? ◦ Has there been a reduction in the hyporheic exchange? Shields Engineering LLC
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Key questions for defining solutions
Has wood in the watershed ever been harvested? How large were riparian trees under old-growth conditions? How have riparian forest conditions changed over time? What was undisturbed historic floodplain? What is current floodplain?
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Pop quiz The municipal government of Ukiah, CA wants to add LW to a 1.5 mile reach of the Russian River adjacent to their town You are the consultant What questions do you ask?
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Hydrologic changes
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Geomorphic changes
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Water quality changes
Recent temperature record and habitat requirements from Manning
resistance tolerance
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More key questions for defining solutions
What are the width, depth, and gradient of the channel?
How do undisturbed historic channel characteristics compare to current conditions? ◦ Bed substrate ◦ Sinuosity ◦ Anabranching (presence of ephemeral and perennial side channels) ◦ Hydraulic geometry (unvegetated width and depth) ◦ Alluvial landforms
Has the channel experienced aggradation or incision?
What is the current instream wood loading in terms of pieces and volumes?
How have infrastructure decisions governed the management of wood? Shields Engineering LLC
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A nice tool
https://www.webapps.nwfsc.noaa.gov/apex/f?p=275:101:::NO:::
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Large wood addition is not for everybody
Should address an existing habitat deficiency ◦ Physical diversity ◦ Cover ◦ Velocity shelter ◦ Substrate sorting ◦ Pool development
◦ Undercut banks ◦ Sites for terrestrial plant colonization
LW density should be depressed relative to references Shields Engineering LLC
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Geomorphic/hydraulic criteria
Channel stability—Goldilocks ◦ ◦ ◦
Erosion processes ◦ ◦ ◦
Best when toe erosion is the primary bank erosion process Not recommended for sites dominated by piping, mass failure or avulsion Not recommended for banks > 85% sand (flanking hazard)
Photo courtesy Natural Channel Design
Sediment load ◦ ◦
Not too unstable Not too stable Slightly aggradational
Generally not suitable for high energy streams actively transporting cobbles. LW may be rapidly buried in high sediment load reaches
Bed material ◦
Anchoring will be difficult in hard beds such as cobble, boulders or bedrock Photo courtesy Interfluve
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Geomorphic/hydraulic criteria
Flow velocity. Reports vary. See TS 14J ◦ Rootwads 2.7 to 3.7 m/s ◦ “well anchored structures”—2.5 m/s ◦ ELJ in sandbed stream—1.2 m/s
More quantitative analysis described below
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Factor of Safety, LWDS 24, event of Nov 29, 2001 LTH1 Comparision of velocities, event of Nov 29, 2001 LTH1 4.5
2500 4.5
3.0 2.5 2.0 1.5 1.0 0.5 0.0 6:00
2000
4.0 3.5
1500 3.0 2.5
1000
2.0
500
1.5
10:48
13:12
1000
velocity within LWDS
velocity at channel centerline
600 400 200
0
0
0.5
6:00
-500 15:36
8:24
10:48
13:12
-200 15:36
TIME
TIME Flow depth
800
1.0
0.0
8:24
1200
VELOCITY, mm/s
FLOW DEPTH, M
3.5
1400
VELOCITY, MM/S
FACTOR OF SAFETY AND FLOW DEPTH, m
4.0
critical velocity for D50 Depth from 1A
Factor of safety--buoyant forces
Depth from 2C
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Velocity within LWDS
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Bed shear as a Function of Stem Density Lopez and Garcia, 1997 Dimensionless bed shear velocity
1.0
0.8 0.5 0.3
Moral: As stem density (LW porosity) declines due to LW breakup or loss of members, trapped sediments are subject to scour.
0.0 0.0001
0.01 1 Ha, dimensionless stem density
Large wood addition is not for everybody
Raw material (large wood) availability
Site access for heavy equipment (or $$$ for helicopter)
Conveyance should permit some LW
Navigation, recreation
Downstream infrastructure Shields Engineering LLC
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Your comments and questions?
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