culvert design for low and high gradient streams
TRANSCRIPT
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Culvert Design for
Low and High Gradient Streamsin the Midwest
Dale Higgins, Hydrologist
Chequamegon-Nicolet National Forest
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Overview
• Culvert Design Considerations– Hydraulic Terms
– Culvert Impacts
• Low vs High Gradient Design
• Low Gradient Culvert Design
• High Gradient Culvert Design
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Culvert Hydraulics Terms
• Invert, Headwater (HW), Tailwater (TW)
• Headwater/Depth Ratio (HW/D): HW / pipe depth
• Supercritical Flow: high velocity, shallow water
• Subcritical Flow: low velocity, deep water
Plunge pool
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Aquatic Organism PassageCulvert Impacts
Depth, Velocity and
Exhaustion Barriers
Jump Barriers
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Sediment SourcesCulvert Impacts
Road Surface Erosion
Scour
Embankment Erosion
Frequent Failures
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Upstream PondingCulvert Impacts on Channel Morphology
• Caused by culverts set too high or sediment
deposits from frequent failures
• Result in stagnant water and upstream
sediment deposition of muck, silt and sand
• Can increase water temperature
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Culvert Design Methods
Low Gradient: No Slope, Tailwater Control
High Gradient: Stream Simulation
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Low vs High Gradient
• Low Gradient = Tailwater Control
• Key Considerations
– Channel slope and bedform lengths
– Culvert length (fill ht, skew, side slope)
– Headcut potential (slope, channel type/material)
– Tailwater control
• Approximate Slope Breaks
– Low gradient < 0.3 percent
– High gradient > 1.0 percent
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Low GradientLow vs High Gradient
Water Surface Slope ~ 0.1%
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High GradientLow vs High Gradient
Water Surface Slope ~ 1.4%
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All Good Culvert Designs Require:
• Complete Field Survey
– Stream profile
– Stream x-sec (2 up, 2 down)
– Road profile (and x-sec)
– Plan view sketch and/or topographic survey with total station
• Hydrologic Analysis
– Design flood flow (100-yr with HW/D<1, check 500-yr)
– Frequent flood flow (1.5 or 2-yr to check model accuracy)
– Fish passage flows (1 and 99% duration, ave daily flows)
– By-Pass flows during construction (ave monthly, median)
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Culvert Size and Bankfull WidthLow Gradient Culvert Design
• Bankfull Width– Straight segment
– Narrow
– Unaffected by road crossing
• Bankfull Width - Riley Cr Example– Min = 7.0 feet
– Mean = 9.2 feet
– Range = 7.0-11.5 feet, n=6
• Select Culvert Width > BF Width
• Compare H&H Width to BF Width
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Low Gradient Culvert Design
• Field Survey
• Hydrologic Analysis
• Select Invert Elevation (and Skew)
• Hydraulic Analysis - Model Flows
• Finalize Design
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Culvert SkewLow Gradient Culvert Design
• Determine culvert skew
• Affects culvert length
• May affect stream profile
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Culvert ElevationLow Gradient Culvert Design
• Set flat (on low gradient streams)
• Check profile for channel morphology impacts
• Consider channel adjustment and restoration
• Consider plunge pool and tailwater longevity
• Ensure tailwater will provide good depth and low velocity in culvert
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Specify Invert ElevationLow Gradient Culvert Design
94
95
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-250 -200 -150 -100 -50 0 50 100 150 200 250 300
Distance (ft)
Ele
va
tio
n (
ft, lo
cal
da
tum
)
Stream Thalweg
Water Surface
Road Surface
Existing Culvert Invert
Existing Culvert Top
New Culvert
Riley Cr at FR 2161
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Specify Culvert ElevationLow Gradient Culvert Design
88
89
90
91
92
93
94
95
96
-150 -100 -50 0 50 100 150 200
Distance (ft)
Ele
vati
on
(ft
)
Stream
Water
Road
Culvert Invert
New Culvert Invert
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Low Gradient Culvert Design
• Field Survey
• Hydrologic Analysis
• Select Invert Elevation (and Skew)
• Hydraulic Analysis - Model Flows
• Finalize Design
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42”x29” CMP ProfileLow Gradient Culvert Design – Riley Cr at FR 2161 Example
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87”x63” CMP ProfileLow Gradient Culvert Design – Riley Cr at FR 2161 Example
Culvert 7.25 ft wide
BF Widths: Min=7.0 ft
Mean=9.2 ft
Max=11.5 ft
N=6
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72”x54” CMP, Culvert TableLow Gradient Culvert Design – Riley Cr at FR 2161 Example
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Low Gradient Culvert Design
• Field Survey
• Hydrologic Analysis
• Select Invert Elevation (and Skew)
• Hydraulic Analysis - Model Flows
• Finalize Design
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Finalize DesignLow Gradient Culvert Design
Road Construction• Surfacing, low point, ditches,
side slopes
• Erosion control: riprap, silt
fence, by-pass, re-vegetation
Culvert Elevation, Size, Type, Shape, Length and Skew• Flood and fish passage flows
• Channel morphology
• Channel restoration
• Fill height and side slopes
• Stream-road alignment
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24
Stream SimulationHigh Gradient Culvert Design
Premise: provide a channel
through the structure that will
present no more of a challenge
to organisms than the natural
channel.
(i.e., pass water, organic
matter, sediment and aquatic
organisms)
How? Use a reference reach to
guide design of a simulated
channel through the structure
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Stream simulation
does not provide:
• Riparian functions
especially bank vegetation
• Light
• Lateral channel and
floodplain processes
• Passage of some aquatic,
semi-aquatic or terrestrial
organisms
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Stream Simulation Design Process
Determine bed shape
and material
Mobility / stability
Assess stream
simulation feasibility
Define structure width,
elevation, details
Design profile control
Examine profile and alignment
Find reference reach Unstable channel
Aggrading or alluvial fan
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Suitable for stream simulation – most
sites in the midwest
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Stream Simulation Design Process
Determine bed shape
and material
Evaluate mobility/stability
Assess stream simulation feasibility
Define structure width,
elevation, details
Design profile controls
Examine profile
and alignment
ID reference reach
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Longitudinal ProfilePhase 2: Pre-emption at FR 377
Preemption Cr at FR 377Chequamegon-Nicolet NF
85.00
86.00
87.00
88.00
89.00
90.00
91.00
92.00
93.00
94.00
95.00
96.00
97.00
98.00
99.00
100.00
101.00
102.00
-325 -300 -275 -250 -225 -200 -175 -150 -125 -100 -75 -50 -25 0 25 50 75 100 125 150 175 200 225 250 275 300
Distance (ft)
Ele
vati
on
(ft
) .
Stream ThalwegWater SurfaceRoadExisting Culvert InvertExisting Culvert TopX-Section Locations
Existing
Culvert
5.0' x 3.0'
1
2
3
4
5
6 7
8 9
10
11
12 13
14
Debris
Jam
(# 1)
Boulder Step
and Log (# 2)
Step at Base of
Cobble/Boulder
Cascade
(# 3)
Culvert
Plunge
Pool
Woody
Debris
(# 4)
Bend
Bend w/
Some
Wood
(# 5)
2.4%
2.3%
1.0%
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Design Slope and Vertical Adjustment PotentialPhase 3: Pre-emption at FR 377
Preemption Cr at FR 377Chequamegon-Nicolet NF
85.00
86.00
87.00
88.00
89.00
90.00
91.00
92.00
93.00
94.00
95.00
96.00
97.00
98.00
99.00
100.00
101.00
102.00
-325 -300 -275 -250 -225 -200 -175 -150 -125 -100 -75 -50 -25 0 25 50 75 100 125 150 175 200 225 250 275 300
Distance (ft)
Ele
vati
on
(ft
) .
Stream ThalwegWater SurfaceRoadExisting Culvert InvertExisting Culvert TopX-Section Locations
Existing
Culvert
5.0' x 3.0'
1
2
3
4
5
6 7
8 9
10
11
12 13
14
Debris
Jam
(# 1)
Boulder Step
and Log (# 2)
Step at Base of
Cobble/Boulder
Cascade
(# 3)
Culvert
Plunge
Pool
Woody
Debris
(# 4)
Bend
Bend w/
Some
Wood
(# 5)
Ave Slope = 2.25%
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Stream Simulation Design Process
Determine bed shape
and material
Mobility / stability
Assess
stream simulation feasibility
Define structure width,
elevation, details
Design profile control,
transitions
Examine profile and alignment
Find reference reach
![Page 32: Culvert Design for Low and High Gradient Streams](https://reader034.vdocuments.us/reader034/viewer/2022042702/6265ca6dce5b8662982d4518/html5/thumbnails/32.jpg)
Selection of reference reach
• Represents stream type through
crossing
– Gradient
– Width/depth
– Channel materials – pebbles
count and key pieces
– Bedforms
• Provides design parameters for
stream simulation
• Out of influence of existing crossing
• Try to avoid very complex channels
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Channel Cross-Sections 5-3Phase 2: Pre-emption at FR 377
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Stream Simulation Design Process
Determine bed
shape & material
Mobility / stability
Assess
stream simulation feasibility
Define structure width,
elevation, details
Design profile control,
transitions
Examine profile and alignment
Find reference reach
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Stream Bed Particle SizesDuck Creek at Hwy 139
Particle size distribution
from pebble count
Streambed mix from
particle size distribution
Perform pebble count
Measure 10 key (largest) pieces
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Stream Simulation Design Process
Determine bed shape &
material
Mobility / stability
Assess
stream simulation feasibility
Define structure width,
elevation, details
Design profile control,
transitions
Examine profile and alignment
Find reference reach
![Page 37: Culvert Design for Low and High Gradient Streams](https://reader034.vdocuments.us/reader034/viewer/2022042702/6265ca6dce5b8662982d4518/html5/thumbnails/37.jpg)
Structure type and width(width >BF to allow for bank rocks and floodplain)
Embedded Round
Pipe Arch
Box
Bottomless Arch
Bridge
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Structure SelectionPhase 3: Pre-emption at FR 377
• Options:– 12’x8’5” Ellipse
– 9’x12’ Concrete Box
– 12’3” Aluminum Box
• Invert Elevations:– Up = 91.2
– Center = 90.5
– Down = 89.8
• Bed Elevations:– Up = 94.2
– Center = 93.5
– Down = 92.8
• Fill Over Pipe = 3 ft
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Stream Simulation Design Process
Determine bed shape &
material
Sediment mobility/stability
Assess
stream simulation feasibility
Define structure width,
elevation, details
Design profile control,
transitions
Examine profile and alignment
Find reference reach
![Page 40: Culvert Design for Low and High Gradient Streams](https://reader034.vdocuments.us/reader034/viewer/2022042702/6265ca6dce5b8662982d4518/html5/thumbnails/40.jpg)
Hydraulic modeling (HEC-RAS) and modified
critical sheer stress equation
40
Primary Considerations:
• Key pieces must be stable: bank rocks, grade controls
• Simulation and reference bed mobilize at same flow
• If upstream replacement unlikely, need most of bed stable
Sediment Mobility and Stability
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Stream Simulation Design Process
Determine bed shape &
material
Mobility / stability
Assess
stream simulation feasibility
Define structure width,
elevation, details
Design profile control, transitions
Examine profile and alignment
Find reference reach
![Page 42: Culvert Design for Low and High Gradient Streams](https://reader034.vdocuments.us/reader034/viewer/2022042702/6265ca6dce5b8662982d4518/html5/thumbnails/42.jpg)
Profile control options
grade controls – rock bands
•Riffle or riffle/step structures
•Constructed with a band of primarily larger (D84-D100)
size unsorted rocks.
•They help form channel cross-section and profile shape.
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Preemption Cr at FR 377Chequamegon-Nicolet NF
85.00
86.00
87.00
88.00
89.00
90.00
91.00
92.00
93.00
94.00
95.00
96.00
97.00
98.00
99.00
100.00
101.00
102.00
-325 -300 -275 -250 -225 -200 -175 -150 -125 -100 -75 -50 -25 0 25 50 75 100 125 150 175 200 225 250 275 300
Distance (ft)
Ele
vati
on
(ft
) .
Stream ThalwegWater SurfaceRoadExisting Culvert InvertExisting Culvert TopX-Section Locations
Existing
Culvert
5.0' x 3.0'
1
2
3
4
5
6 7
8 9
10
11
12 13
14
Debris
Jam
(# 1)
Boulder Step
and Log (# 2)
Step at Base of
Cobble/Boulder
Cascade
(# 3)
Culvert
Plunge
Pool
Woody
Debris
(# 4)
Bend
Bend w/
Some
Wood
(# 5)
Ave Slope = 2.25%
Culvert
Streambed
Design Profile: Culvert and Bed ElevationsPhase 3: Pre-emption at FR 377
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Project ConstructionDuck Creek at Hwy 139
Walk behind front-end loader
Painted bed and bank lines
Streambed and bank rocks
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Low gradient:
Set it low and let it flow!
(No Slope -Tailwater Control)
High gradient:
Simulate the stream!
(Stream Simulation)
Culvert Design Methods