Case Study: The Trans Canada Highway Bridge at Beaver River, Glacier National Park 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 Background: 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 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 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) Affects of erosion at a bridge Case Study:
River bank erosion of Beaver River at the Trans Canada Highway Bridge 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 Our purpose
• Why is the river eroding the bank? • How fast is the bank being eroded? • What are the implications of this bank erosion? 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 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) 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 Drainage area of the Beaver River 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 Major Field Observations Site Diagram Major Field Observations Assessment Field Methods: Flow measurements
• “Pooh sticks” • Large error associated with method • More accurate methods: –Weir – Flow meter – Dye testing 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 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 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 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 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 Results: Assessment
Rapid Assessment of Channel Stability Weighted Stability Indicator Rating Weight Value Bank soil texture and coherence 60.63.6 Average bank slope angle 11 0.6 6.6 Vegetative bank Ratings Values Overall R protection 80.86.4 Excellent (1-3) R < 32 Bank cutting 90.43.6 Good (4-6) 32 <= R < 55 Mass wasting or bank Fair (7-9) 55 <= R < 78 failure 90.87.2 Bar development 60.63.6 Poor (10-12) R >= 78 Debris jam potential 11 0.2 2.2 Obstructions, flow deflectors and sediment traps 90.21.8 Channel bed material consolidation and armouring 30.82.4 She a r stre ss ra tio 81 8 High flow angle of approach to bridge 20.81.6 Bridge distance from meander impact point 10 0.8 8 Percentage of channel constriction 20.81.6 Total --56.6 Overall Rating (R ) --Fair Results: Flow measurements
Flow Rate Estimations
2.5
2 1.95
1.5 1.30 1.14 1
Flow Rate (m/s) Flow Rate 0.5
0 Upstream of bridge Just before bridge Downstream of bridge Location
• 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 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… Sample C
Results: 45.0 •0.8m from 38.6 40.0 35.0 surface 30.0 Sediment 25.0 20.0 •Highest amt 15.0 12.0
Percent (%) Percent 8.7 8.2 10.0 4.6 4.6 4.8 4.7 4.6 4.5 4.7 muds, some sieve 5.0 0.0 2.000 1.700 1.400 1.000 0.710 0.595 0.500 0.355 0.125 0.075 < very coarse 0.075 sand analysis Sieve Size (mm) Sample B •1.2m from 35.0 28.6 30.0 surface, in 25.0 organic layer 20.0 13.4 15.0 12.6
Percent (%) Percent 10.0 5.4 5.2 5.3 6.2 6.0 5.6 5.5 6.1 •Mainly muds, 5.0 0.0 some very fine 2.000 1.700 1.400 1.000 0.710 0.595 0.500 0.355 0.125 0.075 < sand 0.075 Sieve Size (mm)
Sample A •1.7m from 35.0 31.3 30.0 surface 25.0 20.0 16.1 14.3 •Highest amt 15.0 of very fine Percent (%) Percent 10.0 4.7 4.7 4.7 4.8 4.8 4.7 4.8 5.2 5.0 sand 0.0 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) Results: Pebble counts
Pebble Count for Upstream Bar
57 60 50 38 40 • Show slight 30 20 difference 10 5
Number of Pebbles of Number 0 0 downstream < 3 (medium pebble) > 3 < 6.4 (large > 6.4 < 26 (cobble) > 26 (boulder) pebble) • Likely due to Grain Size (cm) change in flow Pebble Count for Bar Closest to Bridge
• Need more 80 75 70 58 60 locations for this 50 40 data to truly be 30 20 6 10 Number of Pebbles of Number 1 useful 0 < 3 (medium pebble) > 3 < 6.4 (large > 6.4 < 26 (cobble) > 26 (boulder) pebble) Grain Size (cm) Results: Aerial photo analysis
1994 1986
2004
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 Results: Historical climate/drainage data
Beaver River (at mouth) - Flow and Precipitation 450 700 • Represents
400 600 glacial input to 350 discharge 500
300 WSC Discharge • Evidence of
/s) Rate 3 400 250 Average relationship other factors
Annual 200 300 Precipitation* influencing Golden Discharge Rate (m Total Precipitation (mm)
150 discharge other 200 than 100
100 precipitation 50
0 0 1988 1991 1994 1997 2000 2004 Year
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 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) 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=__KiKSL2f QG-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%3D 1%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