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River Bank Erosion Case Study: The Trans Canada Highway Bridge at Beaver River, Glacier National Park

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Page 1: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

River Bank Erosion

Case Study: The Trans Canada Highway Bridge at Beaver River,

Glacier National Park

Page 2: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Introduction

• The Beaver River is incising the bank near the eastern abutment of the bridge of the Trans Canada Highway

• The implications of this potentially include a wash out of the TCH, which would be devastating to transportation, tourism and the BC economy

Page 3: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Background: River Bank Erosion

• What causes river bank erosion?

• 2 main mechanisms:• Bank scour• Mass failure

Page 4: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

What is bank scour?

• The direct removal of bank materials by the action of flowing water and the sediment it carries

• Flow rate is a major factor

Page 5: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

What is mass failure?

• A section of the bank slides or falls into the river (collapse or slumping)

• Common with undermining of the toe of the bank

Page 6: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Contributing factors to erosion:• Flooding• Land use and stream management• Clearing of river bank vegetation• River straightening• Rapid flow drop after flooding• Saturation of banks from non-river sources• Redirection and acceleration around

infrastructure or debris in the channel• Intense rainfall events• Bank soil characteristics (easily erodible, poor

drainage)

Page 7: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Affects of erosion at a bridge

Page 8: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Case Study:

River bank erosion of Beaver River at the Trans Canada Highway Bridge

Page 9: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

What we did• Why did we do this?• History of the area• Observations and Methodology

– Assessment– Flow measurements– Discharge measurements– Pebble count– Sediment collection and sieve analysis– Aerial photo review– Historical climate and discharge trends

• Results– Field results– Lab results

• Conclusions• Implications

Page 10: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Our purpose

• Why is the river eroding the bank?• How fast is the bank being eroded?• What are the implications of this bank

erosion?

Page 11: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Background history

• CPR first built railway through here in 1885• The Rogers Pass section of highway was

completed in 1962• Highway dips into the Rocky Mountain

Trench (east of Rogers Pass)• Trench created by a major fault, limestone

of the Rockies to the east and metamorphic rocks of the Selkirks to the west

Page 12: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

More background• TCH is a major transportation corridor• Through traffic in GNP increases by about

1-2% annually

TCH thru traffic 1960 to 2001 (Parks Canada)

Page 13: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

The Beaver River

• A tributary of the Columbia River• Main source is the Beaver Glacier in GNP• Mouth is at the Kinbasket Lake• Total drainage basin = 1,150 km2

• Max discharge in 1985 (429m3/s on May 20th)

• Major flood in July 1983

Page 14: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Drainage area of the Beaver

River

Page 15: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Bridge History

• Bridge length = 42 metres• Single abutment mid-span• Concrete• Age unknown, possibly

original (1962) but has more recent characteristics (adapted for snowplows)

• Some armouring on east side

Page 16: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Major Field Observations

Page 17: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Site Diagram

Page 18: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Major Field Observations

Page 19: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Assessment

Page 20: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Field Methods: Flow measurements

• “Pooh sticks”• Large error associated with

method• More accurate methods:

– Weir– Flow meter– Dye testing

Page 21: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Field Methods: Discharge estimates• Measurement of channel width

and depth to get a cross-section• Channel width - tying a rock to

the end of the measuring tape and throwing it across the channel

• Channel depth – wading in where possible, otherwise guessing

• Large error associated with these methods

• Need waders, measuring tape and ruler – take depth measurements at intervals to get an idea of bed morphology

Page 22: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Field Methods: Pebble count• Established transects along point bars upstream and near

the bridge• Sampled approx every 5 metres along transect, measuring

3 axes of 10 random pebbles• Should have conducted at more locations, and one

downstream

Page 23: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Field/Lab Methods: Sediment collection & sieving

• Collection of 3 samples at eroding bank– Near water level, in organic layer, above

organic layer• Subject samples to standard set of

sieves• Weigh each sub-sample• Should have used hydrometer for silts and clays

Page 24: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Lab Method: Aerial photos

• Acquired aerial photographs from 1986, 1994 and 2004

• Attempted to measure movement of channel meanders, point bars and banks

• Unfortunately, most photos were at too small of a scale

Page 25: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Lab Method: Historical climate and discharge trends

• Examined maximum instantaneous discharge records for the WSC site “Beaver River at Mouth”

• Compared discharge events to precipitation levels over the same time period

• Goal: to determine the impact of non-precipitation sources on discharge

• Too many possible causes of discharge variation

Page 26: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Results: AssessmentStability Indicator Rating Weight

Weighted Value

Bank soil texture and coherence 6 0.6 3.6Average bank slope angle 11 0.6 6.6Vegetative bank protection 8 0.8 6.4Bank cutting 9 0.4 3.6Mass wasting or bank failure 9 0.8 7.2Bar development 6 0.6 3.6Debris jam potential 11 0.2 2.2Obstructions, flow deflectors and sediment traps 9 0.2 1.8Channel bed material consolidation and armouring 3 0.8 2.4Shear stress ratio 8 1 8High flow angle of approach to bridge 2 0.8 1.6Bridge distance from meander impact point 10 0.8 8Percentage of channel constriction 2 0.8 1.6Total - - 56.6Overall Rating (R ) - - Fair

Rapid Assessment of Channel Stability

Ratings Values Overall RExcellent (1-3) R < 32

Good (4-6) 32 <= R < 55Fair (7-9) 55 <= R < 78Poor (10-12) R >= 78

Page 27: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Results: Flow measurements

• Notice a decrease in flow rate from upstream of the bridge to downstream

• Possibly due to channel deepening or widening or subsurface flow

• Likely due to crude methodology

Flow Rate Estimations

1.95

1.301.14

0

0.5

1

1.5

2

2.5

Upstream of bridge Just before bridge Downstream of bridge

Location

Flow

Rat

e (m

/s)

Page 28: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Results: Discharge estimates • From estimated cross-section and estimated

velocity:– Discharge = 19.99 m3/s

• Compare with WSC hydrometric data for Sept 10 to 11th

• Ratio of average discharge over 2 days to the drainage area = 33.38 m3/s : 1150 km2

• and ratio of discharge over 2 days to OUR drainage area = x : 437 km2

• X = 12.68 m3/s• We were a little off…

Page 29: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Results: Sediment

sieve analysis

•1.7m from surface

•Highest amt of very fine sand

•1.2m from surface, in organic layer

•Mainly muds, some very fine sand

•0.8m from surface

•Highest amt muds, some very coarse sand

Sample C

8.74.6 4.6 4.8 4.7 4.6 4.5 4.7

8.212.0

38.6

0.05.0

10.015.020.025.030.035.040.045.0

2.000 1.700 1.400 1.000 0.710 0.595 0.500 0.355 0.125 0.075 <0.075

Sieve Size (mm)Pe

rcen

t (%

)Sample B

5.4 5.2 5.3 6.2 6.0 5.6 5.5 6.1

13.4 12.6

28.6

0.05.0

10.015.020.025.030.035.0

2.000 1.700 1.400 1.000 0.710 0.595 0.500 0.355 0.125 0.075 <0.075

Sieve Size (mm)

Perc

ent (

%)

Sample A

4.7 4.7 4.7 4.8 4.8 4.7 4.8 5.2

31.3

16.1 14.3

0.05.0

10.015.020.025.030.035.0

2.000 1.700 1.400 1.000 0.710 0.595 0.500 0.355 0.125 0.075 <0.075

Sieve Size (mm)

Perc

ent (

%)

Page 30: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Results: Pebble counts

• Show slight difference downstream

• Likely due to change in flow

• Need more locations for this data to truly be useful

Pebble Count for Upstream Bar

5

38

57

00

10

20

30

40

50

60

< 3 (medium pebble) > 3 < 6.4 (largepebble)

> 6.4 < 26 (cobble) > 26 (boulder)

Grain Size (cm)Nu

mbe

r of P

ebbl

es

Pebble Count for Bar Closest to Bridge

6

75

58

10

1020304050607080

< 3 (medium pebble) > 3 < 6.4 (largepebble)

> 6.4 < 26 (cobble) > 26 (boulder)

Grain Size (cm)

Num

ber o

f Peb

bles

Page 31: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Results: Aerial photo analysis

1986

1994

2004

Page 32: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure
Page 33: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Results: Aerial photo analysis

• Evidence of bar migration and change in river morphology

• A gross estimate of rate of erosion based on aerial photos

• We couldn’t calculate one

Page 34: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Results: Historical climate/drainage data

• Represents glacial input to discharge

• Evidence of other factors influencing discharge other than precipitation

Beaver River (at mouth) - Flow and Precipitation

0

50

100

150

200

250

300

350

400

450

1988 1991 1994 1997 2000 2004Year

Disc

harg

e Ra

te (m

3 /s)

0

100

200

300

400

500

600

700

Tota

l Pre

cipi

tatio

n (m

m)

WSCDischargeRate

Averagerelationship

AnnualPrecipitation*Golden

Page 35: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure
Page 36: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Conclusions

• Why is the river eroding the bank?– Due to river meander – aggravated by high

flow events in summer months, less-cohesive bank material, debris obstructions, poor riprap construction

• How fast is the bank eroding?– Changes noted in the aerial photos but nothing

directly related to the current erosion

Page 37: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

Conclusions

• What are the implications?– Undermining of bridge construction– Wash out of TCH– Closure of TCH would have huge impact on

• tourism (especially in summer months during high flow periods)

• economy (main route from BC to the east)

Page 38: River Bank Erosion - University of  · PDF fileBackground: River Bank Erosion • What causes river bank erosion? • 2 main mechanisms: • Bank scour • Mass failure

References• Fahnestock, R.K., Morphology and Hydrology of a Glacial Stream – White River, Mount Rainer

Washington (1963), Geological Survey Professional Paper 422-A • Lagasse, P.F., Schall, J.D., Richardson, E.V., Stream Stability at Highway Structures Third Edition,

(2001), National Highway Institute, US Department of Transportation, Publication No. FHWA NHI 01-002

• Woods, J.G., Glacier Country, (2004), Friends of Mount Revelstoke and Glacier, BC, ISBN 0-921-806-16-7

• http://www.wsc.ec.gc.ca/hydat/H2O/index_e.cfm?cname=WEBfrmPeakReport_e.cfm• http://www12.statcan.ca/english/census06/data/trends/Table_1.cfm?T=CSD&PRCODE=59&GeoCo

de=39019&GEOLVL=CSD• http://www.th.gov.bc.ca/trafficData/tradas/inset3.asp• http://www.transcanadahighway.com/britishcolumbia/TCH-BC-E5.htm• http://atlas.nrcan.gc.ca/site/english/maps/archives/national_park/mcr_0219?maxwidth=800&maxheig

ht=800&mode=navigator&upperleftx=4160&upperlefty=464&lowerrightx=7360&lowerrighty=3664&mag=0.125

• Google Earth• http://images.google.com/imgres?imgurl=http://www.glossary.oilfield.slb.com/files/OGL98036.jpg&

imgrefurl=http://www.glossary.oilfield.slb.com/DisplayImage.cfm%3FID%3D202&usg=__KiKSL2fQG-t5i2scmDiz4iWGsxI=&h=400&w=393&sz=69&hl=en&start=1&um=1&tbnid=cGZW6haL7-ve7M:&tbnh=124&tbnw=122&prev=/images%3Fq%3Dudden%2Bwentworth%2Bscale%26um%3D1%26hl%3Den%26rls%3Dcom.microsoft:en-ca:IE-SearchBox%26rlz%3D1I7GGLR%26sa%3DN

• http://www.pc.gc.ca/docs/v-g/bc/glacier/pd-mp/sec8/page1_E.asp• www.arcc.osmre.gov/HydroToys.asp• http://www.usbr.gov/pmts/hydraulics_lab/workshops/flowmeasurementworkshop_files/swoff

er.jpg