culvert design for low and high gradient streams

Culvert Design for

Low and High Gradient Streamsin the Midwest

Dale Higgins, Hydrologist

Chequamegon-Nicolet National Forest

Overview

• Culvert Design Considerations– Hydraulic Terms

– Culvert Impacts

• Low vs High Gradient Design

• Low Gradient Culvert Design

• High Gradient Culvert Design

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

Aquatic Organism PassageCulvert Impacts

Depth, Velocity and

Exhaustion Barriers

Jump Barriers

Sediment SourcesCulvert Impacts

Road Surface Erosion

Scour

Embankment Erosion

Frequent Failures

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

Culvert Design Methods

Low Gradient: No Slope, Tailwater Control

High Gradient: Stream Simulation

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

Low GradientLow vs High Gradient

Water Surface Slope ~ 0.1%

High GradientLow vs High Gradient

Water Surface Slope ~ 1.4%

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)

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

Low Gradient Culvert Design

• Field Survey


• Select Invert Elevation (and Skew)

• Hydraulic Analysis - Model Flows

• Finalize Design

Culvert SkewLow Gradient Culvert Design

• Determine culvert skew

• Affects culvert length

• May affect stream profile

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

Specify Invert ElevationLow Gradient Culvert Design

94

95

96

97

98

99

100

101

102

103

104

105

106

-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

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


• Field Survey




• Finalize Design

42”x29” CMP ProfileLow Gradient Culvert Design – Riley Cr at FR 2161 Example

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

72”x54” CMP, Culvert TableLow Gradient Culvert Design – Riley Cr at FR 2161 Example


• Field Survey




• Finalize Design

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

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

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

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

Suitable for stream simulation – most

sites in the midwest


Determine bed shape

and material

Evaluate mobility/stability

Assess stream simulation feasibility


elevation, details

Design profile controls

Examine profile

and alignment

ID reference reach

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%

Design Slope and Vertical Adjustment PotentialPhase 3: Pre-emption at FR 377


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

) .


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%


Determine bed shape

and material


Assess

stream simulation feasibility


elevation, details

Design profile control,

transitions


Find reference reach

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

Channel Cross-Sections 5-3Phase 2: Pre-emption at FR 377


Determine bed

shape & material


Assess



elevation, details


transitions



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


Determine bed shape &

material


Assess



elevation, details


transitions



Structure type and width(width >BF to allow for bank rocks and floodplain)

Embedded Round

Pipe Arch

Box

Bottomless Arch

Bridge

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



material

Sediment mobility/stability

Assess



elevation, details


transitions



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



material


Assess



elevation, details

Design profile control, transitions



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.


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

) .


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

Project ConstructionDuck Creek at Hwy 139

Walk behind front-end loader

Painted bed and bank lines

Streambed and bank rocks

Low gradient:

Set it low and let it flow!

(No Slope -Tailwater Control)

High gradient:

Simulate the stream!

(Stream Simulation)

Culvert Design Methods

culvert design for low and high gradient streams

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