Design of Stream-Road Crossings for Aquatic Organism ... · • Fine-grained beds are special...
Transcript of Design of Stream-Road Crossings for Aquatic Organism ... · • Fine-grained beds are special...
Design of Stream-Road Crossings for Aquatic Organism Passage in Vermont
6 – Stream Simulation 1
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Passage Design Process
Pre-Design
Design: Stream Simulation, No slope, Hydraulic, or other
FINAL DESIGN
Or other option
Project Objective
Project profile and alignment
Assessment, Suitability
Select design method
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Vermont Alternative Designs
To satisfy objectives of aquatic organism passage, alternative designs should meet these
performance standards:
– Maintain bed composition and structure• Bed and bedforms• Profile consistent with adjacent reaches• Embedded for life of the project
– Maintain velocities, turbulence and depths of adjacent reaches
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Culvert Design for Fish Passage
RemovalReplacementRetrofit
Adjust profile
Fishway
Roughness
Baffles NaturalBedRegradeRoughened
channelGradecontrols
New
Ecological solutions at Road Crossings- +
AOP
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Flood capacity
Floodplain Continuity
Permit valleyand Floodplain
Processes
HydraulicDesign Pass target species Stream Simulation
Pass sediment, debris, all aquatic organisms.
Ecological solutions at Road Crossings- +
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And this is was our conclusion – stream simulation
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Design method determined by project objectives
Project objectives• Habitat protection, restoration• River and stream continuity• Passage of fish• Passage of other aquatic organisms• Wildlife passage• Traffic, road, safety, other• Funding limits and requirements• Regulatory
Design methods
• Hydraulic
• Stream Simulation
• Low slope (active channel, No slope)
• Alternative designs
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Stream Simulation - Premise
• Low-slope: The design of an oversized culvert in a low risk site can be simplified and built with little risk
• Hydraulic: A structure with appropriate hydraulic conditions will allow target species to swim through it.
• Stream Simulation: A channel that simulates characteristics of the adjacent natural channel, will present no more of a challenge to movement of organisms than the natural channel.
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Stream Simulation Design
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What is stream simulation?
• Geomorphic design
• Simulate natural channel reference reach
– Bankfull cross section shape and dimensions
– Channel slope
– Channel structure
• Channel type
• Mobility – Process, not just structure 15
Stream Simulation Conceptual Details
• Equilibrium with stream gradient and alignment.• Contain stream bed to match to bankfull width and height or
more.• Sustain channel bed shape, bed forms, elevation.
• sediments are transported from and into structure.• culvert bed is mobile; key features are permanent
• Survive floods• Embedded to account for scour, grade adjustments, footings,
bed integrity.
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Stream Simulation Design Process
• Watershed, Road
• Site assessment
• Physical survey
• Continuity
Bed shape and material
Mobility / stability
AssessmentStream simulation feasibility
Structure width, elevation, details
Design profile control
Project alignment and profile
Verify reference reach
Assess >>17
Some things stream simulation does not do within the culvert
• Riparian function– Natural bankline – cohesive soil, root structure– Food production– Flood refuge– Passage of terrestrial species?
• Light• Lateral channel and floodplain processes
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Road Impounded Wetlands
• Stream simulation doesn’t apply because there is no continuity with reference reach. Other solutions might apply Yakima River
Oxbow
Reference reach
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Suitable for Stream Simulation
• Rock, sediment dominated• Equilibrium
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Stream Simulation Design Process
• Reference reach is simulated
• Template for dimensions, slope, bed, features
• Continuity with reference reach
Bed shape and material
Mobility / stability
AssessmentStream simulation feasibility
Structure width, elevation, details
Design profile control
Project alignment and profile
Verify reference reach
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Reference Reach
• Reference reach is simulated– Template for stream simulation dimensions, slope, bed
• Therefore geomorphic processes• Therefore AOP
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Selection of Reference Reach
• Represents project channel– Primarily selected by project gradient– Consider confinement of project– Length of project reach
• Nearby, adjacent, upstream?– Provides “input” to stream simulation– Must be “connected” to crossing
reach– Out of the influence of existing
crossing
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Stream Simulation Slope
• Substantial experience up to 6%• Some successful experience up to 15%• Recommend slope ratio not greater than 1.25
Abby CulvertSlope: 14%
Step-pool Bed Bob Barnard
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Stream Simulation Design Process
• Project objective
• Simulate reference channel
bed material
• Margins, banklines, forcing features
• Bed forms, shape
Bed shape and material
Mobility / stability
AssessmentStream simulation feasibility
Structure width, elevation, details
Design profile control
Project alignment and profile
Verify reference reach
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Bed Design Objectives
• Simulate natural bed– Bed shapes– Diversity– Roughness– Mobility– Forcing features– Control of permeability
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Bed Design by M&B* Channel Types
Based on channel type of reference reach– Dune-ripple; construct or recruit– Pool-riffle / Plane-bed; construct and
let form develop– Step-pool, forced channels; construct
steps– Cascades; construct
– Bedrock– Clay
Incr
easi
ng s
lope
Dec
reas
ing
mob
ility
* Montgomery and Buffington, 1997 27
Bed Material Design – Alluvial
• New installations: use undisturbed channel (consider contraction)
• Replacements: use reference reach gradation.• Pebble count of reference channel for
D100, D84 and D50
• Include dense gradation based on D50 for smaller material and impermeability.
• Fine-grained beds are special cases.
• Compensate for stability of initial disturbed condition.
• Account for large roughness and forcing features.
0
20
40
60
80
100
0.01 0.1 1 10Relative grain sizes
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Well-graded Bed Material
02468
101214161820
Gravel BoulderCobble
%Fi
ner
Sand
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0
10
20
30
40
50
60
70
80
90
100
0.1 1.0 10.0 100.0 1000.0
Grain sizes (mm)
Perc
ent f
iner
than
F-T n=0.45
F-T n=0.70
Stossel Tribreference reach
sand gravel cbl boulder
Small grains derived by Fuller-Thompson curve based on D50
Larger particles sized directly from reference channel
Verify 5% fines are included
Bed Material Design – Alluvial
Stossel Tribexample
Fuller-Thompson
P = percent finerd = diameter of particlen = Fuller-Thompson density; varies 0.45 to 0.70
Simplify to:D16 = 0.321/n x D50D5 = 0.101/n x D50
n
DdP ⎥
⎦
⎤⎢⎣
⎡=
100
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Bed Material ExampleW Fk Stossel Cr
D5
Fines
Fuller-Thompson(assume n=0.7)
Strm SimReference
D16
D50
D84
D100
3”
10”
30”
50% cobble and boulder34% gravel16% medium gravel and fines
Which is:
5-10%
3”= 0.321/n x D50
= 0.101/n x D50
0.59”
0.11”
3”10”30”
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Bed Material Example
• 1 scoop bank run dirt• 4 scoops 4” minus pit run• 4 scoops 8” minus cobbles (or quarry spalls)• 2 scoops 1.5’ minus rock• 1.5 to 2.5 foot rock added during installation
W Fk Stossel Cr – 6.4% slope
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BankfullWidthHeight
Shoulder (or bankline if continuous)
Channel margins
~ 51
10 ft initial low flow channel
RockBand
Stream Simulation BedChannel cross-section
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Rock Bands
Streambedmaterial
Space the lesser of: 5 times the width of channel or max. vertical difference between crests < 0.8 feet
Rock bands (D100 = 1 to 2
times bed D100)
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Flat bed without roughness or banklines.
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Darby Ck. rock bands just after construction
Barnard - WDFW
Darby Ck. rock band during first flood. Band has
altered; flow is centered.
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Alluvial bed material mix
Profile View
Plan View
Step boulders simulate natural steps and spacing
Bank boulders
Culvert
Natural steps
Steps
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Step pool channel
“Set up” step pools and forcing features
Steps
Alluvial bed material mix
Step boulders simulate natural steps and spacing
Culvert
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Special bed design considerations
• Bedform diversity• Bed permeability• Channel cross-section• Banklines• Key features• Small-grain beds
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Margin, bank
Reference channel shape
Debris
Margins, Banklines
Bankline or bands
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Hydraulic, Bank diversity
Ore Creek, Oregon
From USFS, 2006
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Stability of Banks and Key Features
• key pieces are likely permanent– Stability analysis
• Particle entrainment equations• Or bank protection design
Blue CreekLolo Nat’l Forest
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Bed material example design and specW Fk Stossel Cr
5-10%Fines24” rock scattered at
15’ oc throughoutSpanning 6-12” debris
at 50’ spacingColluvium,
debris
0.1”sandD5
36” bankline rock at 25’ spacing or continuous
each bank
Bankline root structure protrudes 3’ at 25’
spacing
Banklines
DesignReference
D16
D50
D84
D95
0.6”
3”3”
10”10”
30”30”
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Bed Retention Sills
• Purpose: retain bed material• Bed retention sills are not baffles or
weirs• Recommended maximum height
equal to half of depth of bed• Debatable value
– Anchors bed; keeps bed from sliding out of culvert
– Anchors bed steps– May conflict with function of
stream simulation– Safety factor for steep slopes
Bed Sill
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Stream simulation in gravel, sand clay beds
Ranch Cr., TX 46
Bed material in channelswith small grain material
• Lower risk with high bed mobility • Less practical to design detailed bed material• When D84 < 20 mm
– Use natural bed material– Select borrow
• Does bed satisfy objective?– If mobile, allow natural filling
• Risk of timing, headcut?• Consider volume of culvert fill• Channel constriction could be
significant issue• Consider temporary sills to retain bed
Select Borrow
0 - 15150 um
30 – 704.75 mm
70 – 10025 mm
10075 mm
% by weightSieve size
Example spec
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Last thoughts on bed material
• Mobility is a key to design of bed• No good spec or source for fine-grained bed other than the
channel itself• Carefully select and supervise source, mixing, and placement• Mitigate the mess• Round vs angular rock?• Does it meet project objective?
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Stream Simulation Design Process
Bed shape and material
Mobility / stability
AssessmentStream simulation feasibility
Structure width, elevation, details
Design profile control
Project alignment and profile
Verify reference reach
• Profile range
• Sustainability
• Floodplain function, connectivity
• Safety factor
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Diameter, D or rise
Round Pipe
50% D maximum
Range of possible bed elevation from long profile analysis (VAP)
Bed profile elevation; average of mobile bedcross section
2’ or per scour analysis or foundation design
Bottomless Pipe
80% D; suggested maximum submergence
Culvert Rise, Elevation
Pool depth plus2.0 x D100 or min % of D
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Stream SimulationHow big is it?
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Culvert Size1. Based on Project Objectives:
• Passage of aquatic, non-aquatic species• Bed sustainability and stability • Hydraulic capacity of the culvert• Construction, repair, and maintenance needs • Protection of floodplain habitats
Barnard
Bankfull Width
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Culvert Size2. Based on Site Conditions:
• Expected future channel width, location• Risk of blockage by floating debris or beaver activity• Large bed material relative to culvert width• Channel skew with road crossing • Ice plugging in severe cold climate
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Stream SimulationFirst estimate of culvert width
First estimate: Culvert width to fit over
channel banks
Bankfull width
Banks
Stream simulation bed
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Stream Simulation culvert width
a. Confined
c. Unconfinedwith floodplain culverts
b. Unconfinedwith wider culvert
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Unconfined channel - consider these modifications• Hydraulic / Stability analysis when floodplain conveyance high• Increase culvert width• Improve inlet contraction• Add floodplain culverts (when either Q10 floodplain > 4 x BFW ?)• Add road dips• Increase bed material size
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Reference channelbankfull cross section
Floodprone width
Road Fill Road Dip
Floodplain culvert in flood swale
Culvert width including floodplain
2. Design the culvert to fit
1. Design the channel and floodplain
Design for sustainability
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Stream Simulation Design Process
Bed shape and material
Mobility / stability
AssessmentStream simulation feasibility
Structure width, elevation, details
Design profile control
Project alignment and profile
Verify reference reach
• Failure modes
• Sustainability of stream simulation (mobility)
• Stability of key pieces
• Culvert capacity(regardless of design method) 60
Mobility / Stability AnalysisThree purposes
1. Is channel shape and bed material stream simulation? –project objective– Project objectives still satisfied?– Driven by moderate flood - bankfull to 50-yr flood?
Mobility
Stability
2. Does bed stay in place?– Banklines, key pieces stable?– Can fail at high flows– Gradual chronic failure
3. Is culvert stable?– Extreme flows– Headwater, pressurized pipe– Debris is usually a greater risk than flow– Diversion
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Culvert Failure
Cedar FlatsThurston Co, WA12/2007
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Stimson Ck.Width ratio = 1.0Slope = 2.2% (5%)
Originalprofile
Culvert too narrow, bed material too small.
Note regradeBed Failure
Resultingprofile
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Xt. Salt CkWidth ratio = 1.1
Slope = 2.9%
Rock bed control at inlet…
led to culvert bed failure
Bed Failure
Originalprofile
64Minimize lengthAdd safety factor to stability analysis *
Long culvert
• Limit headwater depth *• Larger culvert, additional culverts *
Pressurized pipe
• Verify potential profilesDownstream channel instability
• Compact bed• Consolidate bed• Increase bed material size
Lack of initial bed structure
• Larger culvert, Additional culverts *• Increase bed material size *
Floodplain contraction
• Minimize slope increase• Increase bed material size *• Increase bed culvert width *
Steeper than reference reach
Stream simulation culverts
• Build sag in road• Design for plugging, failure
Stream diversion
• Limit headwater depth• Efficient upstream transition
Debris blockage, flows
All culvertsDesign/construction strategyRisk
Ris
ks a
nd D
esig
n/co
nstru
ctio
n st
rate
gies
* = bed mobility / stability analysis required
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Mobility / Stability Analysis - Process
• Mobility: compare design reach to reference reach– Design of D84 mobility the same in both channels
• D84 is important – roughness, form, mobility• One possible design assumption
– Calibrates analysis; therefore not sensitive to hydrology– Analyze for sensitivity
• Stability: analyze key pieces at high stability design flow
• Is it real? – Test sensitivity of parameters and compare alternatives.– Compare results to reference channel. – Is it a natural conclusion or are you forcing the channel? 66
Unit discharge – Bathurst (1987)
• Developed in: – steep channels; 0.23 < S < 9.0%, – Course bed material; 9 < D84 < 280 mm
• Lab and field data• relative submergence (water depth/D50) less than 10
or less than 4 (water depth/D84).
12.1
5.150
5.0
5015.0
SDgqcD =
b
icDci D
Dqq ⎟⎟
⎠
⎞⎜⎜⎝
⎛=
5050
⎟⎟⎠
⎞⎜⎜⎝
⎛=
84
165.1DDb
Critical unit discharge for D50
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Procedure using Bathurst
12.1
5.150
5.0
5015.0
SDgqcD =
b
icDci D
Dqq ⎟⎟
⎠
⎞⎜⎜⎝
⎛=
5050
⎟⎟⎠
⎞⎜⎜⎝
⎛=
84
165.1DDb
Assumptions: • Total flow is the same in stream simulation and reference channels.• D84 has equal mobility in both channels.
FP
b
cD QwDD
SDgQ +
⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛=
50
8412.1
5.150
5.0
8415.0
Procedure:• Arrange Bathurst equations for total flow and set equal.• Vary conditions of stream simulation channel so total flow is the same.• Confirm floodplain flow.• Recalculate conditions(There are other possible assumptions, procedures) 68
FP
b
c QwDD
SDg
Q +⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛=
50
8412.1
5.150
5.0
8415.0
FP
b
c QwDD
SDg
Q +⎥⎥⎦
⎤
⎢⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛=
50
8412.1
5.150
5.0
8415.0
equals
Reference channel Stream simulation channel
⎟⎟⎠
⎞⎜⎜⎝
⎛=
84
165.1DDb⎟⎟
⎠
⎞⎜⎜⎝
⎛=
84
165.1DDb
Qc84 is flow in the active channel
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Schafer Cr trib
ScAnalysis >>70
Key Pieces - Stability Analysis
• Key pieces are permanent (up to stability design flow)• What is stability design flow?• Stability models - analytical
– Bathurst– Corps bank riprap– Corps rock chute– Moment stability analysis
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D = median particle diameterq = discharge per unit widthS = energy slopeg = acceleration of gravity – 9.8 m/s
Sf = Safety FactorCv = Vertical velocity distribution coefficient
= 1.0 straight channel (R/W>26)= 1.0 inside of bend= 1.283-0.2log(R/W)
CT = Thickness coefficient> 1.0 when thickness > Dmax
Cs = Stability coefficient= 0.30 for angular rock= 0.375 for rounded rock?
γs = unit wt of rockγW = unit wt of waterα = Bank slopeφ = Rock angle of repose - + -43º
13/1
432.03/231
15
8550 '
KgSqC
DD
D ⎟⎟⎠
⎞⎜⎜⎝
⎛=
⎥⎦
⎤⎢⎣
⎡−
−=φα
γγγ
αTanTanCosK
ss
s11
⎥⎦
⎤⎢⎣
⎡−
=ws
wsTvf CCCSC
γγγ785.0)(3.5'
Corps model for Steep slopesCorps EM 1110-2-1601
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Barnard
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Failure. Risk consideration
Life of project, Tr
40%
20%
10%
5.0%
1.0%
50 years20 years10 years
Probability of occurrence (failure?)
Calculated design flow for specific project durations
n
r
rn T
TP ⎥⎦
⎤⎢⎣
⎡ −−=
11
100 yr40 yr20 yr
225 yr90 yr45 yr
500 yr200 yr100 yr
1,000 yr400 yr200 yr
5,000 yr2,000 yr1,000 yr
n = yearsTr = return intervalP = probability
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The point is …
Design conservatively.
Design for failure.
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6-Mile CkWidth ratio = 0.9
Slope = 5%Downstream control lost
Bed failureAt approx 500-yr flood
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Diversion Culvert plugs and initiates stream diversion.
Flow diverted to other stream or scours new channel
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DebrisIn forested watersheds, debris is the most prevalent cause of culvert failure. Culvert alignment is a major contributor to debris-caused failures.
Solutions: Culvert width, alignment, and transition.
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Culvert Capacity
• Review range of project profiles.
• Analyze capacity with the high profile.
• Consider headroom and elbow room for debris.
• With debris, alignment critical.• Review risk of diversion.• What are consequences of
failure?
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80
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83
84
85
86
87
88
89
90
91
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0 100 200 300 400 500 600
Distance (ft)
Ele
vatio
n (ft
)
StreambedWater SurfaceOld Pipe
Existingpipe invert
Culvert elevations, capacity
Range of potentialProfiles (VAP)
83.0 low profile bed
85.0 high profile bed
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Elev 89.1
80% of rise
Elev 78.0
Alluvial pool depth+ 2 x D100
Final culvert designBox culvert 14.8’ wide x 12’ high
Culvert elevations
83.0 low profile bed
High Profile
Q100 = 92 cfs
86.9 at Q100 HP
85.0 high profile bed
Other height considerations:• debris headroom,• cover, • vertical alignment
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O’Grady Cr – 2002
Reference ChannelD84 = 52 mmBFW = 11 ft
Stream simulation solution • Culvert 14.8 ft w x 12.0 ft h• D84 = 50 mm• D100 = 130 mm (or by key pieces)
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Some last thoughts on stream simulation
• It isn’t this complicated. Use the tools that are appropriate.
• Check your conclusions with reality
84
Bob Gubernick
Standard const equip
PremixedKim Johansen, USFS
Stream Sim Construction
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Bed Material Placement
•Dingo Loader
•Manually
•Trail equip
•Special equip
Rock Chute
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Upper Stillwell Creek Case Study15-ft. Span Structural Plate Arch
2-ft. x 4-ft. x 82-ft. Concrete Footings
Adding stream simulation bed over a layer of 4’-minus well-graded select borrow.
Barb Ellis-Sugai, Geomorphologistand Rob Piehl, Civil Engineer
88 89
Design of Stream-Road Crossings for Aquatic Organism Passage in Vermont
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90 91
Pringle Ck.
Stream width 9.1 ft, slope 5%Culvert bed width 9.3 ft, slope 6%
Unit Power = 6.3 ft-lb/sec/ft3Barnard
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Bankfull width structure after 16 years
Johansen
Width ratio: 1.0, slope 4.5%