Monitoring, Modeling, and Assessment of Scour Critical Bridges in

Robin A. Beebee

Hydrologist U.S. Geological Survey Alaska Science Center In Cooperation with the Alaska Department of Transportation and Public Facilities and the Corporation

This information is preliminary and is subject to revision. It is being provided to meet the need for timely best science. The information is provided on the condition that neither the U.S. Geological Survey nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.

Photos by author except where noted The Alaska Streambed Scour Program

Contributors Jeff Conaway (USGS) Karenth Dworksy (USGS) Schyler Knopp (USGS) Paul Schauer (USGS) Micah Claypoole (USGS) Mike Knapp (AKDOT&PF) Hiram Henry (AKDOT&PF)

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Assessment – Monitoring - Assessment

Partnership between the Alaska Department of Transportation and Public Facilities and the U. S. Geological Survey since 1964, with additional support from the Alaska Railroad.

Started as a way to better understand scour and sediment movement at gravel-bedded rivers in Alaska. The initial study (Norman, 1975) measured hydraulic variables and streambed elevations during floods at 11 bridges.

The U.S. Geological Survey began a large-scale phased assessment program throughout the state in 1994. In 2001, real-time monitoring of a subset of scour-critical bridges was initiated in part to fulfill a mitigation strategy for scour-critical bridges until counter-measures or replacement could occur.

Preliminary Information-Subject to Revision. Not for Citation or Distribution. Figure of scour measured at a pier from Norman, 1975 The Alaska Streambed Scour Program Assessment

• Over 400 bridges in 20- plus years • Phased approach to assessments • Phase 1-2 and Tidal were 1D models with increasing amounts of field-specific data. • Phase 3 includes 2D models and future phases will include sediment transport. Conaway, 2004; Heinrichs and others, 2007; Langely, 2006; Heinrichs and others, 2001; Conaway and Schauer, 2012; Beebee and Schauer, 2015; Beebee and others, 2017; Preliminary Information-Subject to Revision. Not for Citation or Distribution. Beebee and others, 2019 The Alaska Streambed Scour Program Monitoring

• 27 bridges have been instrumented with sonars at some point, 15 are currently monitored with sonars and 3 are stage-only with soundings.

• Monitoring fulfills part of the scour critical plan of action for these bridges • Bridges are added as repeat soundings and/or assessments indicate need • Monitoring discontinued when bridges are replaced/retrofitted/closed, or monitoring indicates little scour during major floods.

Conaway and Brabets, 2010; Dworsky and Conaway, 2018 Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Monitoring Methods

• 200kHz pier-mounted sonar, usually on upstream side of bridge, with 8-degree beam, fixed or retractable for ice. • Ultrasonic stage sensor mounted on rail or deck • CR1000 datalogger, Iridium satellite modem, power supply • Verified with annual or semi-annual soundings. • Most sites only monitored during ice-free season. • Some sites have only stage and soundings. Sheridan River scour monitoring site, 2013

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Kasilof River winch-raised sonar mount

Photo by Jeff Conaway, 2005

2014

Preliminary Information-Subject to Revision. Not for Citation or Distribution. 2014 The Alaska Streambed Scour Program Copper 1187 winch-raised sonar mount and footing

Both photos, Copper River at 1187, 2019

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Montana/Kashwitna sliding sonar mount

Kashwitna River raised 2016 Montana Creek lowered 2015 Preliminary Information-Subject to Revision. Not for Citation or Distribution. 2020 The Alaska Streambed Scour Program Nenana at Ferry sliding sonar mount

Nenana River, 2015

Nenana River, 2015

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Tanana fixed sonar mount for ice/debris

Tanana River at Nenana, 2014 Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Tanana armored mount in action

Tanana River, Jeff Conaway, 2008 Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Verifying sonar depths with soundings

Lead weights Copper River, Jeff Conaway, 2010

ADCP on tethered boat Montana Creek, 2015

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Verifying sonar depths – RC boat and ice drill

ADCP on remote controlled boat – 20-Mile River, 2020

Steam drill and ice rod, Nenana River, 2015 Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Near real-time data is streamed to website: https://www.usgs.gov/centers/asc/science/streambed-scour-bridges-alaska Soundings are also uploaded to the website

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Results of Monitoring 27 bridges since 2002

Scour observed Other without flooding, Flooding all three still observed monitored without scour, 2 4 5 partially 3 monitored, 2 monitored, 1 replaced 5 Neither flooding nor scour 10 Both flooding observed, 3 still monitored, and scour 4 retrofitted/replaced, 3 observed, 3 discontinued closed, 2 monitored

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program

Twelve sites are no longer monitored because: • 1 countermeasures were installed • 5 replaced with new bridges • 3 closed when part of Copper River Highway was closed because of bridge failure • 4 because little to no scour was measured Copper River Highway at Bridge 339 in 2011

Preliminary Information-Subject to Revision. Not for Citation or Distribution. Photo by Jeff Conaway, 2011 The Alaska Streambed Scour Program Scour in Absence of Major Flooding Events Knik River, Chilkat River, Copper at 1187. Knik River Example.

Knik River bridge sonar in winter, Knik River bridge, 4:1 contraction ratio old bridge visible upstream

Matanuska-Susitna Borough Imagery, 2016 Preliminary Information-Subject to Revision. Not for Citation or Distribution. and Photo by Schyler Knopp, 2017 The Alaska Streambed Scour Program Scour in Absence of Major Flooding Events Bridge 539: Knik River Stage & Sonar 2013 62 Pier 56 Sonar Elevation Stage 50 Design high water elevation Stream Bed Elevation 44 6/21/2013 Sounding

38 7/2/2013 Sounding 8/1/2013 Sounding 32

10/29/2013 Sounding Built Built Elevation, feet in

- 26 As 20 Estimated 100-year scour 14

8 5/1/2013 5/26/2013 6/20/2013 7/15/2013 8/9/2013 9/3/2013 9/28/2013 10/23/2013 11/17/2013 Date

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Scour in Absence of Major Flooding Events Bridge 539: Knik River (2013-2015)

70

60

Bridge geometry 50 As-built cross section

10/29/2013 US 40 8/21/2014 US

6/25/2015 US 30

7/30/2015 US

BUILT ELEVATION, IN FEET -

AS 20 9/17/2015 US

10 0 100 200 300 400 500 DISTANCE FROM THE LEFT BANK ABUTMENT, IN FEET

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Scour in Absence of Major Flooding Events

New Knik River Bridge, 505 feet long 20 feet of scour at 29,000 cfs

Old Knik River Bridge, 2000 feet long 3.5 feet of scour at 235,000 cfs

Preliminary Information-Subject to Revision. Not for Citation or Distribution. See Norman, 1975 and Conaway, 2006 The Alaska Streambed Scour Program Scour in Absence of Major Flooding Events Maximum scour depth of 3.5 ft

Old Knik River Bridge at 235,000 cfs

Preliminary Information-Subject to Revision. Not for Citation or Distribution. Photo and figure from Norman,1975 The Alaska Streambed Scour Program Scour AND Flooding Events Sheridan River, 20-Mile River, and Eastern Copper Delta. Sheridan River example.

Approach to Sheridan River during flood Sheridan River during flood

Preliminary Information-Subject to Revision. Not for Citation or Distribution. Photos by Paul Schauer, 2014 The Alaska Streambed Scour Program Scour AND Flooding Events Bridge 230: Sheridan River Stage & Sonar 2014 50

Estimated 100-year flood Pier 45 Estimated design flood Sonar Elevation 40 Stage

35 Stream Bed

30 7/22/2014

Sounding BUILT ELEVATION, BUILT ELEVATION, FEET IN - 25 9/16/2014

AS Sounding

20 Estimated 100 year scour 15 5/26/2014 6/26/2014 7/27/2014 8/27/2014 9/27/2014 DATE

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Scour AND Flooding Events

55 Bridge 230: Sheridan River (2013 - 2014)

50

45

40

Bridge 35 As-built 9/11/2013 US 30 10/23/2013 US

7/22/2014 US built elevation, feet in

- 25

9/16/2014 DS As 9/16/2014 US 20 Estimated 100-year scour 15

10 0 20 40 60 80 100 120 140 160 180 200 DISTANCE FROM THE LEFT BANK ABUTMENT, IN FEET

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Changes to Sheridan Glacier likely increased flooding at Bridge 230

Bridge 230 Bridge 230

1950 aerial photo showing multiple glacial outwash channels 2020 Sentinel Image showing single channel

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Time-lapse imagery (Sheridan) Debris jams on piers exacerbate contraction at the bridge

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Sites with Flooding Events but Little to No Scour Tanana at Nenana, Nenana at Windy, Tok River, Red Cloud River, Lowe River. Tanana example.

Tanana River Bridge 202

Estimated Pier Scour: Phase 1 study: 43.5-45.5 ft Phase 2 2D model: 37.8-40.3 ft (Langley, 2006) Minimal contraction scour

Bridge 202 just after construction, from Alaska Digital Archives, 1967

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Tanana River Bridge 202

Sonar never worked well, despite our best efforts.

365 360 355 350 345 340 335 330 325 Pier 320 Sonar Elevation 315

Stage BUILT ELEVATION, IN FEET - 310 Streambed Elevation AS 305 300 Soundings 295 Off-season work on the Bridge 202 sonar, 2015 May-18 Jun-18 Jun-18 Jul-18 Aug-18 Aug-18 Sep-18 Oct-18

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Sites with Flooding Events with Little to No Scour Soundings showed a few feet of pier scour at most, and almost always during low flow

365

355 BN 202 Geometry As-Built Sounding 345 6/26/2015 US 335 8/20/2015 US 10/8/2015 US 325 Measured 100-year pier scour (1967) 2011 LiDAR Overbanks 315

BUILT BUILT ELEVATION, IN FEET 5/9/2016 US -

AS 305 7/26/2016 US Estimated 100-year pier scour elevation 10/11/2016 US 295 0 200 400 600 800 1,000 1,200 DISTANCE FROM THE LEFT BANK EXPANSION JOINT, IN FEET

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Sites with Flooding Events with Little to No Scour Measurements during major flooding in 1967 and 2008 showed general fill and a maximum local scour of 6 feet at the pier

Tanana River, Jeff Conaway, 2008 Photo from Alaska Digital Archives, 1967

Preliminary Information-Subject to Revision. Not for Citation or Distribution. See Norman, 1975 The Alaska Streambed Scour Program Still waiting for something to happen… Kasilof, Tanana at Big Delta, Tazlina are still monitored of the bridges with neither big floods nor much scour. Other bridges were replaced, retrofitted, or removed from the scour critical list.

Sonar on the Tanana at Big Delta bridge, 2019 Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Kasilof River Bridge 670 After 17 years of monitoring, neither flooding at the design level nor scour has been observed. Flooding is attenuated by a very large natural lake upstream of the bridge.

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Kasilof River Stage and Sonar

44 Estimated 100-year flood 42 Pier 40 Sonar Elevation 38 Stage 36

Bed Elevation built datum (ft) datum built

- Highest recorded stage 34 8/27/2013 Sounding 32

30 Elevation in as in Elevation

28

26 Estimated scour 6/10/2013 7/8/2013 8/5/2013 9/2/2013 9/30/2013 10/28/2013 Date

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Kasilof River Bridge 670 Soundings

56

51

As-built cross section 46 Bridge geometry 8/19/2014 US 8/19/2015 US 41 Sonar 8/11/2016 US 8/25/2017 US 36 9/7/2018 US

9/6/2019 US

BUILT ELEVATION, IN FEET

- AS 31 Lowest recorded sounding (9/2004)

26 Estimated scour 0 50 100 150 200 250 DISTANCE FROM THE LEFT BANK ABUTMENT, IN FEET

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Kasilof River SRH2D Model

SRH2D model mesh Kasilof right bank 2017

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Kasilof River SRH2D Model Channel mapped into V coarse and finer sections based on visible cobbles during low flow. Used two gradations, the rest was classified as “unerodable”.

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Kasilof River Calibrated the model to normal summer high flow surveyed in 2018, then ran the 100-year and 500-year floods using the Meyer-Peter-Mueller transport formula in SRH2D. Maximum scour at the 500 year flood is 0.8 feet at the bridge.

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Kasilof River Bridge Sediment Transport Results

45.0

43.0

41.0

sounding 39.0 SRH2D 100 Year Bed 37.0 SRH2D 100 Year WS SRH2D 500 Year Bed 35.0 SRH2D 500 Year WS 33.0 as-built bridge CalibratedBedElev 31.0 Actual Calibrated WS 29.0 estimated 100-year scour from 27.0 1D model and scour formula

25.0 20 70 120 170 220 270

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Conclusions (so far) 1. Scour assessments are a first step for all bridges but can be inaccurate. FHWA equations don’t take every factor into account, and conditions change, especially in Alaska’s glacial rivers.

2. For critical bridges, scour monitoring works. The streambed scour program assisted in determining:

• Seasonal contraction scour problems at Knik River – big scour does not require big floods.

• Flooding and bridge capacity problems at Sheridan – debris is now removed regularly

• Scour equations overestimate scour at Tanana Bridge 202 and other sites without contraction. The scour critical nature of these Measuring the record flood in 1967 at Tanana River bridges can be re-evaluated. Bridge 202, U.S. Geological Survey

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Conclusions (so far) 3. The best monitoring catches the river in action, sonar data needs to be supplemented with observations and soundings.

4. Monitoring data can also be used to refine assessments and better understand how local factors influence scour. This can lead to more detailed and accurate hydraulic modeling.

5. Monitoring is cost-effective and quick to implement compared to engineering solutions. It is both a safety measure while waiting for an engineering solution and a way to collect more data to better understand the problem. The monitoring of Bridge 339 allowed DOT to decide on a daily basis whether to keep the bridge open, and to close the bridge before any failure occurred.

Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program Not without challenges We also monitor logs!

Kashwitna River 2014

Salcha River 2013 Tanana River 2014, Paul Schauer Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program

References available at: https://www.usgs.gov/centers/asc/science/streambed- scour-bridges-alaska

Norman, V.W., 1975, Scour at selected bridge sites in Alaska: U.S. Geological Survey Water-Resources Investigations Report 32–75, 160 p Heinrichs, T.A., Kennedy, B.W., Langley, D.E., and Burrows, R.L., 2001, Methodology and estimates of scour at selected bridge sites in Alaska: U.S. Geological Survey Water Resources Investigations Report 00–4151, 44 p. Conaway, J.S., 2004, Summary and comparison of multiphase streambed scour analysis at selected bridge sites in Alaska: U.S. Geological Survey Scientific Investigations Report 2004–5066, 34 p.,https://doi. org/10.3133/sir20045066. Langley, Dustin E., 2006, Calculation of scour depth at the Parks Highway bridge on the Tanana River at Nenana, Alaska, using one-and two-dimensional hydraulic models; U.S. Geological Survey Scientific Investigations Report 2006-5023 Heinrichs, T.A., Langley, D.E., Burrows, R.L., and Conaway, J.S., 2007, Hydraulic survey and scour assessment of Bridge 524, Tanana River at Big Delta, Alaska: U.S. Geological Survey Scientific Investigations Report 2006-5282, 66 p

Conaway, J.S., and Brabets, T.P., 2011, Streamflow and streambed scour in 2010 at bridge 339, Copper River, Alaska, in Dumoulin, J.A., and Dusel-Bacon, C., eds., Studies by the U.S. Geological Survey in Alaska, 2010: U.S. Geological Survey Professional Paper 1784-C, 24 p., available at https://pubs.usgs.gov/pp/1784/c/.

Removing a sonar from Bridge 339 on the Copper River, 2016 Preliminary Information-Subject to Revision. Not for Citation or Distribution. The Alaska Streambed Scour Program References available at: https://www.usgs.gov/centers/asc/science/streambed- scour-bridges-alaska

Conaway, J.S., and Schauer, P.V., 2012, Evaluation of streambed scour at bridges over tidal waterways in Alaska: U.S. Geological Survey Scientific Investigations Report 2012–5245, 38 p., accessed June, 2018, at https://doi. org/10.3133/sir20125245.

Beebee, R.A., and Schauer, P.V., 2015, Streambed scour evaluations and conditions at selected bridge sites in Alaska, 2012: Scientific Investigations Report 2015-5154, 45 p., https://doi.org/10.3133/sir20155154.

Beebee, R.A., Dworsky, K.L., and Knopp, S.J., 2017, Streambed scour evaluations and conditions at selected bridge sites in Alaska, 2013-2015: U.S. Geological Survey Scientific Investigations Report 2017-5149, https://pubs.er.usgs.gov/publication/sir20175149.

Beebee, R.A., Dworsky, K.L., and Knopp, S.J., 2019, Streambed scour evaluations and conditions at selected bridge Sites in Alaska, 2016–17: U.S. Geological Survey Scientific Investigations Report 2019-5110, 32 p., https://doi. org/10.3133/sir20195110.

Dworsky, K.L., and Conaway, J.S., 2019, Measurement of long-term channel change through repeated crosssection surveys at bridge crossings in Alaska: U.S. Geological Survey Open-File Report 2019-1028, 118 p., https://doi.org/10.3133/ofr20191028. Bridge 339 on the Copper River, 2019

Preliminary Information-Subject to Revision. Not for Citation or Distribution.