AT Bridge and Culvert Hydraulics Guide

Alberta Transportation, 2011 1

Overview •Hydraulic Modelling Approach •Open Channel Flow •Bridge Constriction •Culvert Hydraulics •Fish Passage – Culverts •Other Factors - Ice, Drift, Scour •Reference Documents

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Hydraulic Modelling Approach

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Hydraulic Modelling Approach •Recommended Modelling Approach •Section averaged (1D), based on typical channel section •Neglect overbank d/s flow component •Account for GVF, RVF where appropriate •Roughness, Slope – use HDG approach •Results – HW EL (freeboard), V (rock sizing)

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Hydraulic Modelling Approach •Accuracy •Don’t Confuse with Precision •Limited by geometry, hydraulics (n, K), other (drift, ice, sediment) •+/- 20% acceptable for Y, V (confidence in parameters) •Consider sensitivity of design •Round Y to 10% (min 0.1m) •Round V to 10% (min 0.1m/s, 0.01m/s for fish passage)

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Hydraulic Modelling Approach •Why not multi-section (HEC-RAS) or 2D? •Boundary conditions – only 1D estimate anyway •Mobile boundary – bedforms, scour, lateral erosion… •Complex factors – drift, ice, sediment transport •No ability to calibrate complex models •Detailed output interpretation – lose impact •No need for additional detail - accurate or not •Unnecessary level of effort, resources ($)

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Hydraulic Modelling Approach •Why neglect overbank d/s flow component? •Small percentage ( h); T – Top Width T

h

B 10

Boundary Conditions – Typ. Channel Typical • • • • • •

:

Evaluate at many sections over nearby channel Focus on relatively straight reaches Avoid areas influenced by past construction B, T – airphotos, survey, DEM h – survey, DEM, site measurements, scale from photos Many values published in HIS

*Images from Google Earth

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Open Channel Flow – Slope •Rise / Run along channel •Determine from DTM (HIS Tool) •“Rise” must be clear (larger than bed irregularities) •Typically requires longer “Run” than is practical to survey •Channel survey expensive, awkward •Structure may have influenced profile within survey

•Sites with slope break near crossing: •Confirm based on channel changes e.g. planform •HDG – focus on u/s channel (flow delivery) •Hydraulics – focus on d/s channel (backwater effect)

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Open Channel Flow – Slope Stream Profile for BF73713 Fish Creek Stream Profile For - FISH on CREEK 1600 Slope Of Line = 0.003 1500

1314

73713

1300

6885

73523

Elevation (m)

1400

1200

1100

1000 10000

15000

20000

25000

30000 Station (m)

13

35000

40000

45000

50000

Boundary Conditions – Roughness •B < 10m – Manning ‘n’ (per HDG, built into Channel Capacity Calculator tool) B

‘n’

S

‘n’ adj

0 – 3m

0.05

< 0.0005 (B > 8m)

- 0.005

4 – 6m

0.045

0.005 – 0.015

+ 0.005

7 – 9m

0.04

> 0.015

+ 0.010

•B >= 10m – Use AT Equation (see WWW page) 0.67 0.4

V = 14 R

S

•Values consistent with observations •Use results in consistent application across system

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Open Channel Flow – Type •No Downstream (D/S) Hydraulic Influence •Normal Flow (Sf = So) •Tool – “Channel Capacity Calculator”

•D/S Hydraulic Influence •Structure – e.g. weir, bridge, culvert, dam •Channel change – slope, width •Gradually Varied Flow (GVF) profile to crossing site •Tool – “Flow Profile”

•U/S Hydraulic Influence – rare (steep, short impact) •Tool – “Flow Profile”

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Boundary Conditions – Normal Flow

Blue – User Input Values Green – Recommend n Value from AT HDGs Red – Calculated Results 16

Boundary Conditions – Rating Curve (Channel Capacity Calculator) 3.5 Rating Curve

3.0

Bank Height Channel Capacity

2.5

Y (m)

2.0

1.5

1.0

0.5

0.0 0

10

20

30

40 Q (cms)

17

50

60

70

80

Open Channel Flow – GVF (Flow Profile – Backwater Curve from D/S Constriction) 105 Energy Gradeline Water Surface EL. Normal Depth

104

Critical Depth Top of Bank Bed 103

102

101

100

99

98 200

180

160

140

120

100

18

80

60

40

20

0

Bridge Constriction

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Bridge Constriction •Bridge Size Optimization •Starting Point – match typical channel •Evaluate range of options – shorter and longer

•Constriction •Bridge provides less flow area than typ. channel •Shorter bridge but more protection works •Will result in higher V (poss. larger rock) •Will result in increased headloss (freeboard, u/s flooding)

•No constriction •Bridge matches or exceeds flow area of typ. Channel •No need for hydraulic modelling – use BC values •Don’t exceed natural channel – lateral stability issues 20

Bridge Constriction •Bridge Constriction Hydraulics – 3 sources of headloss •Flow expansion at d/s side (RVF) •Higher V through constricted section •Flow constriction at u/s side (RVF) 2

2

2 2 – V ) (V (V – V 1 1 ) + SfL + Kc 2 Headloss = Ke 2 2g 2g

;

Sf = n2 V2 or Sf = V5/2 R4/3

Ke = Expansion Loss Coefficient (default = 0.5) Kc = Contraction Loss Coefficient (default = 0.3) V2 = Mean Velocity through Constriction (m/s) V1 = Mean Velocity through Channel (m/s) Sf = Friction slope (energy gradient) through constriction L = Length of Constriction g = acceleration due to gravity (m/s2) n = Manning Roughness coefficient 21

733R5/3

Bridge Constriction - Calculations •Calculation process (subcritical flow): •Start with Boundary Condition D/S •RVF for flow expansion •GVF for constricted flow •RVF for flow constriction •GVF in U/S Channel

•Supercritical and/or combined profiles possible •Tool – “Flow Profile”

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Bridge Constriction - Input

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Bridge Constriction - Input 103.5

103.0

102.5

102.0

101.5

101.0

Channel

100.5

Bridge 100.0

99.5 -20

-15

-10

-5

0

24

5

10

15

20

Bridge Constriction - Output

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Bridge Constriction - Profile 105 Energy Gradeline Water Surface EL. Normal Depth

104

Critical Depth Top of Bank

104

Bed 103 103

102

102

101 101

100

100 200

180

160

140

120

100

26

80

60

40

20

0

Bridge Constriction - Sensitivity 1.6

1

Depth Increase

0.9

1.4

V Ratio 0.8

1.2

1 0.6

0.8

0.5

0.4 0.6

* This plot is specific to the current scenario

0.3

0.4

0.2 0.2

0.1

0

0 0.4

0.5

0.6

0.7

Bridge Bed Width Ratio

27

0.8

0.9

1

V Ratio

Depth Increase (m)

0.7

Culvert Hydraulics

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Culvert Hydraulics •Culvert Size Optimization •Starting Point – Rise = burial + Y + headloss •Evaluate range of sizes, shapes, barrels, profiles •“Culvert Sizing Considerations” (AT webpage) •Practical sizing – drift/ice, future lining (high fills, traffic vols)

•Hydraulics •Always RVF (inlet, outlet) due to different shape •Always GVF (burial provides tailwater) •More profile type possibilities – hydraulic jumps, full flow •Fish Passage evaluation - roughness •AT Tools – “Flow Profile” (main), “HydroCulv” (multiple culverts) 29

Culvert Hydraulics – Sizing Criteria •Upstream Flooding Impacts •Fish Passage •Drift •Icing •End Protection Works •Uplift Failure •Embankment Stability •Road Overtopping •Blockage •Future Rehabilitation •Others… site specific 30

Culvert Hydraulics - Tool Comparison HydroCulv

Flow Profile

First Year

~ 1991

2009

RVF

K * V2/2g

Profile

One Slope

Multiple

Channel

TW Only

Full Context

No. Barrels

Up to 5

1

Sensitivity

Yes – Q,D

Manual

**

**

K * (V2-V1)2/2g

Very conservative (punitive) for well sized culvert 31

Culvert Hydraulics – Flow Profile: Input

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Culvert Hydraulics – Flow Profile: Output Results Summary

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Culvert Hydraulics – Output Detailed Results

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Culvert Hydraulics – Flow Profile: Output 106.0 Invert + Culvert Energy Gradeline

105.0

Water Surface EL. Top of Bank Critical Depth

104.0

Normal Depth

103.0

102.0

101.0

100.0

99.0

98.0 200

180

160

140

120

100

35

80

60

40

20

0

Culvert Hydraulics – Flow Profile: Input

Sensitivity Analysis to Determine Culvert Sizing -Try round pipe, avoid “Full Flow”

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Culvert Hydraulics – Flow Profile: Output 105.0 Invert + Culvert Energy Gradeline Water Surface EL.

104.0

Top of Bank Critical Depth Normal Depth

103.0

102.0

101.0

100.0

99.0

98.0 200

180

160

140

120

100

37

80

60

40

20

0

Culvert Hydraulics – Flow Profile: Input

Sensitivity Analysis, Continued.. -Try elliptical pipe, avoid “Full Flow”

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Culvert Hydraulics – Flow Profile: Output 105.0 Invert + Culvert Energy Gradeline Water Surface EL.

104.0

Top of Bank Critical Depth Normal Depth

103.0

102.0

101.0

100.0

99.0

98.0 200

180

160

140

120

100

39

80

60

40

20

0

Culvert Hydraulics – Flow Profle: Input (Multi-sloped Culvert)

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Culvert Hydraulics – Flow Profile: Output (Multi-slope)

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Culvert Hydraulics – Flow Profile: Output (Multi-slope) 106.0 Invert + Culvert Energy Gradeline

105.0

Water Surface EL. Top of Bank Critical Depth

104.0

Normal Depth

103.0

102.0

101.0

100.0

99.0

98.0 200

150

42

100

50

0

Fish Passage - Culverts

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Fish Passage - Culverts •Principle •Make culvert NOT a velocity barrier to fish •Compare to typical natural channel hydraulics •Use V (section average) as indicator

•Design Flow Parameters •Evaluate at Q > normal, Q < flood •Evaluate over range - sensitivity •Calc Q in channel at typically Y = 0.5 to 1.0m (less than bank height)

•Hydraulics •Burial results in increased flow area, decreased velocity •GVF in barrel (lose burial TW with length – backwater effect) 44

Fish Passage - Culverts

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Fish Passage - Culverts

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Fish Passage - Culverts

Y

Vchannel

Q

Vinlet

Voutlet

0.50

0.8

2.3

0.67

0.49

0.75

1.0

4.5

0.97

0.76

1.00

1.2

7.4

1.26

1.04

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Fish Passage - Culverts 105.0 Invert + Culvert Energy Gradeline Water Surface EL.

104.0

Top of Bank Critical Depth Normal Depth

103.0

102.0

101.0

100.0

99.0

98.0 200

180

160

140

120

100

48

80

60

40

20

0

Fish Passage - Culverts •Velocity Reduction Options - Effective •Increase Pipe Roughness – long culverts, steep grades (normal flow) •Use Multiple Pipes – wide, shallow channels; consider drift blockage •Use Wider Shape (Box, Ellipse) – cost vs bridge

•Velocity Reduction Options – NOT Effective •Increase Pipe Diameter - mostly air space •Increase Burial – ineffective >1m, ponding, u/s barrier, excavation?

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Fish Passage - Culverts 104

Increase Roughness with Rocky Substrate 103

Elevation (m)

102

101

100

99

Substrate 98 -5

-4

-3

-2

-1

0

XS Station (m) 50

1

2

3

4

5

Fish Passage - Culverts •Increase Roughness •Effective – long, steep pipes (Burial TW lost, normal flow) •Install 0.2m – 0.3m thickness rock (e.g. class 1M, 1) •Install metal weirs at regular spacing to retain substrate •Substrate may also act as mitigation measure (DFO)

•Estimate ‘n’ •Based on roughness height of substrate (k ~ 3.5D84) •Equate Manning and Chezy equations •Assume roughness applies to entire ‘P’ (low flow) •Sensitive to flow depth (R), iterative calculations

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Fish Passage - Culverts R1 / 6 n= ⎛ 12 R ⎞ 2.5 g ln⎜ ⎟ ⎝ k ⎠ n = Manning roughness coefficient R = Hydraulic Radius (A/P) g = acceleration due to gravity (9.806m/s2) k = roughness height (m) D84 – bed particle size (m), 84% smaller Rock

D84(m)

k(m)

Class 1M

0.2

0.7

Class 1

0.35

1.2

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Other Factors (Ice, Drift, Scour)

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Ice •Potential Impacts on Structure •High Ice (Ice Jams) may govern Min. Btm. Flg. •Ice Loads on Piers (CAN/CSA-S6-S06, Section 3.12) •Strength (situation) •Elevation •Thickness •Icing (Aufeis) may affect culvert operation/design

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Ice – Ice Jams •High Ice (Ice Jams) •May govern on some large rivers •Difficult to calculate analytically •Consider in developing opening, span configuration •Rely on observations •Historic (on file, dwgs) •Site (ice scars on trees, abrasion on substructure) •Consider u/s and d/s sites, similar sites in the area •Look for Potential Ice Jam Triggers •Change in profile •Major tributary •Natural or man-made constriction 55

Ice – Design Pier Loads •Consider sensitivity of structure to design loading •Base design on observations •Review past designs on stream •Review historic records, site observations •Ice scars on trees •pier nose abrasion, broken piles •U/S winter ice cover •Timing of annual breakup

•If little data, consider ‘typical’ values (next page)

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Ice – Design Pier Loads •Typical values (based on common past practice):

Damage History

Small Stream (B < 50m)

Large Stream (B > 50m)

Minor

Sit. ‘a’ EL ~ 0.8 * Y t ~ 0.6m

Sit. ‘b’ EL ~ 0.6 * Y t ~ 0.8m

Major

Sit. ‘b’ EL ~ 0.6 * Y t ~ 0.8m

Sit. ‘c’ EL – observ. t ~ 1.0m

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Ice - Icing •Icing (Aufeis) •Opening partially blocked by solid ice •Water freezing in place (u/s spring, culvert - burial) •Capacity not there during spring runoff •Prediction – site observations, flood history, MCI

•Mitigation •Bridge •Raise gradeline (upsize) •2nd culvert (higher) •Maintenance (deicing line -$)

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Drift •Potential Impact on Structure •Opening partially blocked, reduced capacity •Culvert – overtopping, u/s flooding, uplift failure •Bridge – damage, pier scour, flow deflection against banks

•Prediction •Historic observations, MCI – flood conditions •Tree density adjacent to stream and tributaries •Low bank stability – provide large trees to stream •Beaver dams •Tree size – largest tree can start accumulation

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Drift - Mitigation •Culvert: •Consider Bridge •Larger Size (likely marginal impact) •Flared inlet (maintain flow with blockage) •Flow alignment piles

•Bridge •Increase minimum centre Span •Maintenance

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Scour •Lowering of streambed •Types: •Natural (passing of bed forms) •Constriction (across channel, increased V) •Bend (outside, secondary currents) •Pier (local, obstruction to flow)

•Impact: •Pier foundation design •RPW design – headslope protection, launching apron

•Difficult to calculate, use practical design (long piles)

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Scour – Estimation Difficulties •Changes in flow alignment (lateral mobility) •Passing bedforms •Variable foundation materials •Weathering of exposed rock •Formation of natural armour layers •Infilling during flood recession •Compounding different scour types •Time dependency •Theoretical equations vs practical observations

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Scour - Mitigation •Use Deep Piled Foundations (BPG No. 7) •River Protection Works (BPG No. 9) •Protect headslopes •Maintain flow alignment – guidebanks, spurs

•Practical design of launching apron length (~ 5*Dmx) •Pier Scour Inspection Program (BIM - existing structures) •Pier Scour Rehabilitation: •RPW – control flow alignment •Structural underpinning •Bed armouring – can exacerbate problem •Accelerated replacement 63

Reference Documents

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Reference Documents •Hydrotechnical Design Guidelines for Stream Crossings •Culvert Sizing Considerations •Guide to Bridge Planning Tools •BPG Tool Application Guide •AT “Flow Profile” Tool documentation •HIS Tool Overview •Evaluation of Open Channel Flow Equations •BPG 7 – Spread Footings •BPG 9 – Rock Protection for Stream Related Infrastructure •BPG 13 – Freeboard at Bridges http://www.transportation.alberta.ca/565.htm

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