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
4.0 Key issues for design
Course overview Day I (Jan 26)—Foundational topics
• 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
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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• Introductions • Review of information resources (design handbooks and spreadsheets) for large wood • Is wood appropriate for your site?—criteria for screening (Planning)
• Types of wood structures • Findings of recent research on drag and lift coefficients
• “Road testing” selected design spreadsheets
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• What kind of wood to use (species, dimensions) • Where to get it, and how to get it to site • What kind of structure to create • What dimensions to use for structure and spacing between structures • Anchoring or not • Impact (effects) analysis • • • • •
Conveyance Sediment transport, deposition, scour Bridges and culverts Habitat Social ….recreation, cultural resources
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If LW is for you, you must decide….
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What is different from previous list?
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List of key issues from TS 14J
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Levels of effort for design
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What are the consequences of failure?
RISK
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• Recreation/public use • Flooding • Erosion and sedimentation • Ecological effects • Infrastructure
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Risk issues (Knutson & Fealko)
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Knutson and Fealko (2014)
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How many structures will be placed and where?
REACH LAYOUT
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• • • • •
Budget Habitat needs Geomorphic transformations Erosion controls Previous/historic/reference wood loading • Anticipated recruitment
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How much wood do we want to add?
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“use natural analogs”
Objectives were to demonstrate use of LW structures to….. • Reduce bank erosion and increase sediment storage • Increase habitat quality (morphological diversity
• All structures without cabling or imported ballast • 350 tonnes of wood • 20 ELJs • Average reach loading of Williams River, Australia 0.014 m3/m2 Brooks (2006), Brooks et al. (2004)
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1100 m reach
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Natural analogs for large wood structures
12 T.B. Abbe, D.R. Montgomery / Geomorphology 51 (2003) 81–107
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Larson's Reach Restoration, Nooksack River, Lummi Indian Nation Natural Resources Dept. (photo: Daniel B. Nylen)
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•
• •
24 Engineered Log Jams (ELJs) 2 km treatment reach of degraded ephemeral sandbed stream Coupled with ~ 20 years of ongoing native revegetation aimed to increase the geomorphic diversity and ecological characteristics
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•
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Stockyard Creek, NSW, Australia
from Hughes (2014)
Small….. • Single pieces • Smaller wood • Channel spanning structures • Toe logs • Create plunge pools
~10 m
Medium to large…. • Larger wood • Multiple piece formations • More anchoring • Deflectors, spur type, secondary channel closure, bank revetment and bar apex type structures
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LW layout differs from small to large channels….
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Density of roughness elements (i.e., ELJs) increases toward the margin of the valley. This type of layout breaks up the channel into smaller and smaller channels or anabranches with distance from the main channel
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“Valley scale� restoration to limit erosion along valley margins
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Little Topashaw Creek, MS Shields et al. (2004)
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http://www.ars.usda.gov/Research/docs.htm?docid=5526
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DESIGN OF INDIVIDUAL STRUCTURES
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How high? How wide? How long? How far apart?
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Rules of thumb for bank protecting spur-type structures • Crest angle • Crest length • Crest elevation • Spacing
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• The angle between a line normal to the approach flow vector and the weir crest should be about 15° upstream to promote deflection of overtopping flow away from eroding banks (Derrick 1997), OR • Angles between the bank and the weir crest of 25– 30° based on straight channel flume tests (Johnson et al. 2001).
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Crest angle
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• Crest length may be based on regression of channel bottom width against drainage area for regional data sets comprised of channels approaching “quasi-equilibrium” (Downs and Simon 2001) • Design crest length will be the difference between current and equilibrium width times the cosine of the crest angle. • Alternatively, crest length may be based on a target flow conveyance for the design cross section.
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Crest length
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• For incised channel with mass failure of banks, crest elevations must be high enough so that the sediment berms that form over the LWDS stabilize existing nearvertical banks. • Stable bank heights and angles may be based on • Geotechnical analyses (e.g., BSTEM) or • Empirical criteria based on regional data sets
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Crest elevation
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• • • • • •
Cable Chain Rebar Threaded rods Rope Wooden pins or pegs
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Fasten logs together?
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Structure spacing (for stability)
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• Spacing between LWS is difficult to prescribe before construction because the dimension of each LWS parallel to the flow direction is dependent upon the diameter and length of the LW members. • In general, though, LWS placed along a given segment of eroding bankline should be spaced 1.5–2.0 times the crest length apart (Petersen 1986). • Spacing should be great enough to provide segments of unprotected bankline between structures to reduce cost and to create physical habitat diversity
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Practical aspects of spacing
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HOLDING WOOD IN PLACE
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This is the hard part
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How will large wood be restrained? • Low risk, no downstream bridges, culverts, etc. • Works well when LW >>>channel width
• Ballast (need cobble and boulders). Will ballast leak? • Vertical pilings (need help from geotechs) • Embedment in banks or bed • Anchors
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• Natural…”parents”
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Report from biologically successful projects
• We evaluated habitat responses at 91 large wood restoration projects in western Oregon from pretreatment to 1 year and 6 years after treatment. • Large logs were arranged in jams without cabling or burial in the bottom or banks of the stream. Projects commonly treated 0.5–1 km of stream, but some extended up to 2.3 km. • …..the amount of large wood decreased in a majority of projects during the 6 years after treatment reflecting net export out of the sites and a lack of recruitment from upstream or local sources.
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Jones et al. (2014)
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Ballast options
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58 of the 72 LWS were anchored using four Duckbill Earth Anchors (138-DB1) each.
Earth anchors Each anchor was driven into the ground by pressing with a metal rod and a track hoe bucket and then load tested to 4.5 kN.
Anchor Installation
Top View of a Completed LWS (note the crossing cables)
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It’s not just a river of water, it’s also a river of sediment.
SEDIMENTATION AND EROSION
31 Doug Shields, Jr.
www.friendofrivers.com
Sedimentation analysis • Deposition/transport capacity
without LWDS with LWDS
• Scour • What to use for sediment discharge into reach? • Lack of calibration problematic
3500
3000
2500
2000
River Station, m
1500
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• Spreadsheet computations • 1-D analysis • 2-D simulations 1000
32 http://water.engr.psu.edu/liu/hydrosed2d.html
• Scour often a primary cause of failure • Scour pools important to habitat • Total scour = S general scour + contraction scour + local scour • Empirical equations for bridge abutments and piers • See guidance provided by Knutson and Fealko (2014), Shields (2007), Cramer (2012: Appendix E), Arneson et al. (2012) • Scour depths are sensitive to structure (LW formation) geometry
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Scour analysis
Pool amplitude (bottom of deepest pool to adjacent crest) is rough indicator of scour magnitude in gravel bed river (Brooks 2006).
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Lagasse et al. 2010窶年CHRP 653 窶｢ Guidelines for predicting the size, location, and geometry of debris accumulations at bridge piers 窶｢ Methods for quantifying scour at bridge piers resulting from debris accumulations 窶｢ Guidance for incorporating debris effects in one- and two-dimensional hydraulic modeling
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Risk analysis for downstream infrastructure
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• Ice??? • Impacts from bedload • Impacts from floating debris (but see Knutson and Fealko 2014) • Beavers??? • Dynamic effects
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“Orphan” issues
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• Make a master list of issues that are important for your project before beginning design process • Use this course plus guidance I have told you about to generate your list
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Design issues—closing thought
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