Environment, Coasts, Oceans, & Infrastructure

​hi all:

I do several ASCE webinars and am thinking of adding another one but want to gauge the interest.

I have seen many mis-applications of HEC-RAS when performing bridge scour studies.  I have compiled 6 so far of the most common mistakes (I will use a total of 8) that I have encountered and would like to present then in a 90 minute webinar that ASCE could market and generate revenues.  I am open to suggestions for more problems that you may have seen and am willing to swap out my proposed problems if deemed that the suggested one are more important.

The topics are:

1. Scour depth for piers should be using hydraulics at the thalweg and applied to all piers within the area of anticipated lateral movement of the main channel.  If you assume that the main channel may move laterally, the worst case is if the thalweg moves to each of the piers - therefore the hydraulics at the thalweg (and resulting scour) should be applied to all piers and the scour depth should be applied to the thalweg elevation to determine the scour ELEVATION at each pier.  The way HEC-RAS displays pier scour is not appropriate.
2. Pier groups that are close together (within 5 pier diameters, per HEC-18) must be model as one pier using the group projected width and if skewed, take into consideration as a group and input to the skew variable in the scour menu.
3. If debris is modeled on the piers for hydraulic considerations, must also add to the pier width for pier scour.
4. Froehlich's pier/abutment scour already has safety factor (essentially 100%) in it so do not have to add a safety factor to the scour results.
5. Don't double count pier skew.  For elongated piers, enter width of pier (not projected width) and add the skew to the scour input.  Enter the projected width for the bridge pier width for the hydraulics.  If the situation is as per item 2 above, use the proper projected width of the pier group for the pier width in the hydraulics.
6. Double check if approach and exit cross sections that are automatically assigned for bridge modeling are at the proper location.  The proper ones to assign are cross sections 1 and 4 of the traditional cross sections used in HEC-RAS bridge modeling.  If there are cross sections between 1 and 2 and between 3 and 4, HEC-RAS assigns the closest downstream cross sections from 2 and closest upstream cross sections from 3.  This affects the contraction and abutment scour computations.
7. Suggestions?
8. Suggestions?

------------------------------
David Williams Ph.D., P.E., PH, D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

I thought of another one.  If a pier sits on a pile cap, the predicted pier scour should be examined to see if exposes the cap. If it does, the pier scour computation should be redone using the projected width and appropriate "nose" shape of the cap.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

A new scour analysis and HEC-18 publication is in editing stages and expected out soon (probably within a year). Just in case this helps inform your decision.

------------------------------
Joanna Curran A.M.ASCE
Dr.
SEATTLE WA
------------------------------

Original Message:
Sent: 11-28-2017 21:36
From: David Williams
Subject: Interest in ASCE webinar short course - Bridge scour analysis

I thought of another one.  If a pier sits on a pile cap, the predicted pier scour should be examined to see if exposes the cap. If it does, the pier scour computation should be redone using the projected width and appropriate "nose" shape of the cap.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

​Joanna:  Thanks for the information on the new upcoming publication.  I'll look out for it.   David

------------------------------
David Williams Ph.D., P.E., D.WRE, HG, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

Original Message:
Sent: 11-30-2017 02:06
From: Joanna Curran
Subject: Interest in ASCE webinar short course - Bridge scour analysis

A new scour analysis and HEC-18 publication is in editing stages and expected out soon (probably within a year). Just in case this helps inform your decision.

------------------------------
Joanna Curran A.M.ASCE
Dr.
SEATTLE WA
------------------------------


Original Message:
Sent: 11-28-2017 21:36
From: David Williams
Subject: Interest in ASCE webinar short course - Bridge scour analysis

I thought of another one.  If a pier sits on a pile cap, the predicted pier scour should be examined to see if exposes the cap. If it does, the pier scour computation should be redone using the projected width and appropriate "nose" shape of the cap.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO

Dr. Curran - Thank you for sharing. I believe the NCHRP Local Abutment Scour method will be tweaked with regards to additional guidance on when to use the clear or live bed scour condition. Do you know what NCHRP report will be incorporated into the new edition?

------------------------------
Jeffrey De Graff P.E., L.S.I.T., M.ASCE
Engineer
Hoyle Tanner and Associates
Burlington VT
------------------------------

Original Message:
Sent: 11-30-2017 02:06
From: Joanna Curran
Subject: Interest in ASCE webinar short course - Bridge scour analysis

A new scour analysis and HEC-18 publication is in editing stages and expected out soon (probably within a year). Just in case this helps inform your decision.

------------------------------
Joanna Curran A.M.ASCE
Dr.
SEATTLE WA
------------------------------


Original Message:
Sent: 11-28-2017 21:36
From: David Williams
Subject: Interest in ASCE webinar short course - Bridge scour analysis

I thought of another one.  If a pier sits on a pile cap, the predicted pier scour should be examined to see if exposes the cap. If it does, the pier scour computation should be redone using the projected width and appropriate "nose" shape of the cap.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO

There is work on-going now from NCHRP RFP 24-47 on clear water and live bed contraction scour in cohesives and fines. An RFP is about to be issued concerning the development of scour equations for gravel bed rivers. Please watch for it if anyone is interested in pursuing the question.
In discussions with the people at federal highways, it sounded like updates to HEC-18 are being edited, so coming out within the year, and they will be planning on incorporating further updates from these projects. No firm date for the release though.

------------------------------
Dr. Joanna Curran A.M.ASCE
SEATTLE WA
------------------------------

Original Message:
Sent: 12-01-2017 06:14
From: Jeffrey De Graff
Subject: Interest in ASCE webinar short course - Bridge scour analysis

Dr. Curran - Thank you for sharing. I believe the NCHRP Local Abutment Scour method will be tweaked with regards to additional guidance on when to use the clear or live bed scour condition. Do you know what NCHRP report will be incorporated into the new edition?

------------------------------
Jeffrey De Graff P.E., L.S.I.T., M.ASCE
Engineer
Hoyle Tanner and Associates
Burlington VT
------------------------------


Original Message:
Sent: 11-30-2017 02:06
From: Joanna Curran
Subject: Interest in ASCE webinar short course - Bridge scour analysis

A new scour analysis and HEC-18 publication is in editing stages and expected out soon (probably within a year). Just in case this helps inform your decision.

------------------------------
Joanna Curran A.M.ASCE
Dr.
SEATTLE WA


Original Message:
Sent: 11-28-2017 21:36
From: David Williams
Subject: Interest in ASCE webinar short course - Bridge scour analysis

I thought of another one.  If a pier sits on a pile cap, the predicted pier scour should be examined to see if exposes the cap. If it does, the pier scour computation should be redone using the projected width and appropriate "nose" shape of the cap.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO

Thanks JoAnna for the info on the manual.  I'll look for it!

Regards
Drew

------------------------------
Drew Baird Ph.D., P.E., D.WRE, M.ASCE
Senior Hyd Eng
US Bureau of Reclamation (86-68540)
Denver CO
------------------------------

Original Message:
Sent: 11-30-2017 02:06
From: Joanna Curran
Subject: Interest in ASCE webinar short course - Bridge scour analysis

A new scour analysis and HEC-18 publication is in editing stages and expected out soon (probably within a year). Just in case this helps inform your decision.

------------------------------
Joanna Curran A.M.ASCE
Dr.
SEATTLE WA
------------------------------


Original Message:
Sent: 11-28-2017 21:36
From: David Williams
Subject: Interest in ASCE webinar short course - Bridge scour analysis

I thought of another one.  If a pier sits on a pile cap, the predicted pier scour should be examined to see if exposes the cap. If it does, the pier scour computation should be redone using the projected width and appropriate "nose" shape of the cap.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO

​Drew:

Since I am located so close to your office in Lakewood, I am willing to do an in-house presentation (when finished creating the material) on this for the BOR is you are interested.. As always to my friends at the BOR, this would be for free.

David

------------------------------
David Williams Ph.D., P.E., D.WRE, HG, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

Original Message:
Sent: 12-05-2017 16:46
From: Drew Baird
Subject: Interest in ASCE webinar short course - Bridge scour analysis

Thanks JoAnna for the info on the manual.  I'll look for it!

Regards
Drew

------------------------------
Drew Baird Ph.D., P.E., D.WRE, M.ASCE
Senior Hyd Eng
US Bureau of Reclamation (86-68540)
Denver CO
------------------------------


Original Message:
Sent: 11-30-2017 02:06
From: Joanna Curran
Subject: Interest in ASCE webinar short course - Bridge scour analysis

A new scour analysis and HEC-18 publication is in editing stages and expected out soon (probably within a year). Just in case this helps inform your decision.

------------------------------
Joanna Curran A.M.ASCE
Dr.
SEATTLE WA


Original Message:
Sent: 11-28-2017 21:36
From: David Williams
Subject: Interest in ASCE webinar short course - Bridge scour analysis

I thought of another one.  If a pier sits on a pile cap, the predicted pier scour should be examined to see if exposes the cap. If it does, the pier scour computation should be redone using the projected width and appropriate "nose" shape of the cap.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO

​I would have an interest in attending such a webinar when available.  Please keep me apprised.
Thanks,
Glenn Eby

------------------------------
Glenn Eby P.E., M.ASCE
Senior Project Manager
JHA Companies
Montrose PA
------------------------------

------Original Message------

​I would have an interest in attending such a webinar when available.  Please keep me apprised.
Thanks,
Glenn Eby

------------------------------
Glenn Eby P.E., M.ASCE
Senior Project Manager
JHA Companies
Montrose PA
------------------------------

​Sanmy:  I have done short courses in sediment transport but they were on-site seminars, not webinars.  David

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

Original Message:
Sent: 11-30-2017 07:54
From: Sanmy Campos
Subject: Interest in ASCE webinar short course - Bridge scour analysis

Good Morning

I'm very interest to take the webinar about the erosion estimation in bridge.

Also, I wondering if you have some kind of course about sediment transportation.

Thanks

--

Ing. Sanmy N. Campos Palma, M.Sc.

Cel.829-479-7220

 

"Diseño, Construcción y Asesoría Técnica en  Sistemas de Abastecimiento de Agua Potable; Sistemas de Alcantarillado Sanitario y Drenaje Pluvial, Plantas de Tratamiento de Aguas Residuales Domésticas, Comerciales e Industriales, Estaciones de bombeo de agua potable y residual;  Caracterización de Afluentes y efluentes; Programas de Manejo y Control de Calidad de aguas; Instalaciones Sanitarias para Edificaciones; Sistemas de Protección Contra incendios; y Asesoría Técnica en Soluciones Ambientales"

Original Message------

​I would have an interest in attending such a webinar when available.  Please keep me apprised.
Thanks,
Glenn Eby

------------------------------
Glenn Eby P.E., M.ASCE
Senior Project Manager
JHA Companies
Montrose PA
------------------------------

If there is a webinar please consider addressing options for filling rip rap to aid in wildlife passage and how that can affect (help or hinder?) bridge scour. ​Some road authorities are making it standard practice to fill rip rap voids prevent barriers to animal movement under the bridge, especially for smaller animals like turtles.  I've heard of using fine aggregate or compost (only placed above the high water line) that can be seeded and covered with ECB to create vegetated side slopes. I did find a paper in the ASCE library that looks at the protective ability of rip rap buried and unburied but I'm not certain of it's applicability.

------------------------------
Carol Andrews P.E., M.ASCE
Environmental Project Manager
Duluth MN
------------------------------

Original Message:
Sent: 11-29-2017 09:19
From: Glenn Eby
Subject: Interest in ASCE webinar short course - Bridge scour analysis

​I would have an interest in attending such a webinar when available.  Please keep me apprised.
Thanks,
Glenn Eby

------------------------------
Glenn Eby P.E., M.ASCE
Senior Project Manager
JHA Companies
Montrose PA
------------------------------

​Carol:

I am not aware of studies or guidelines related to riprap and the issues you point out.  Of the top of my head, my colleagues that may know about it are Dr. F. Douglas Shields, Dr. Gary Freeman, and Dr. Steven Maynord.  Am sure there are others that could help.   David

------------------------------
David Williams Ph.D., P.E., D.WRE, HG, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

Original Message:
Sent: 11-30-2017 10:44
From: Carol Andrews
Subject: Interest in ASCE webinar short course - Bridge scour analysis

If there is a webinar please consider addressing options for filling rip rap to aid in wildlife passage and how that can affect (help or hinder?) bridge scour. ​Some road authorities are making it standard practice to fill rip rap voids prevent barriers to animal movement under the bridge, especially for smaller animals like turtles.  I've heard of using fine aggregate or compost (only placed above the high water line) that can be seeded and covered with ECB to create vegetated side slopes. I did find a paper in the ASCE library that looks at the protective ability of rip rap buried and unburied but I'm not certain of it's applicability.

------------------------------
Carol Andrews P.E., M.ASCE
Environmental Project Manager
Duluth MN
------------------------------


Original Message:
Sent: 11-29-2017 09:19
From: Glenn Eby
Subject: Interest in ASCE webinar short course - Bridge scour analysis

​I would have an interest in attending such a webinar when available.  Please keep me apprised.
Thanks,
Glenn Eby

------------------------------
Glenn Eby P.E., M.ASCE
Senior Project Manager
JHA Companies
Montrose PA

David:

Thanks for sharing your experience with sour analysis errors.  I would be interested in your webinar.

------------------------------
Cordie Qualle P.E., M.ASCE
Industry Faculty Fellow
CSU Fresno
Fresno CA
------------------------------

David, 

   Terrific idea. I've frequently encountered these same topics when reviewing scour calculations. I'd argue the topic of scour is diverse, important, and frequently encountered enough to justify three separate sessions, perhaps an hour each. I could see the following series:

• Scour Primer: Overview of scour processes, types of scour, and primer of general scour equations including contraction scour, pressure scour, "bedform scour", bend scour, and/or general river scour. Perhaps a detailed discussion of contraction scour and general river scour as time allows.
• Focus on Pier Scour: including the topics you mentioned and a primer on available scour equations for special conditions (piers on erodible bedrock, cohesive materials, etc.)
• Focus on Other Types of Commonly-Encountered Scour: abutment, open-bottomed culverts, and perhaps simplified long-term degradation.

   I have a host of ideas that I could share with you on each of these topics off-line, but the most important one, and surprisingly the one I encounter most frequently, is to heed the model warnings about super-critical flow. It's important to note while sub-critical flow may be conservative for floodplain mapping, it is NOT conservative for some scour conditions (or stabilization design for that matter). 

   -James


------------------------------
James Woidt A.M.ASCE
Woidt Engineering & Consulting, PC
Water Resources Engineer
Scarborough, ME
------------------------------

Original Message:
Sent: 11-30-2017 10:45
From: Cordie Qualle
Subject: Interest in ASCE webinar short course - Bridge scour analysis

David:

Thanks for sharing your experience with sour analysis errors.  I would be interested in your webinar.

------------------------------
Cordie Qualle P.E., M.ASCE
Industry Faculty Fellow
CSU Fresno
Fresno CA
------------------------------

​James:

Thank you for your thoughts.  There are other webinars and seminars by ASCE that present the basics of bridge scour such as this one.

Bridge Scour Computations with HEC-RAS

Asce		remove preview
Bridge Scour Computations with HEC-RAS View this on Asce >

The above webinar just goes only through the mechanic of bridge scour using HEC-RAS with no guidance whereas I want to present intricacies in the application of the model.

I too discuss some of these scour topics in my webinars for Forester University (an online short course entity) when I teach about hydraulics, bank protection, scour control and stream restoration.  Right now, I think I will just try to get ASCE to accept my proposal to present on the topics proposed here and then maybe expand to add info that you suggest.

Please provide more of your thoughts.

David

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

Original Message:
Sent: 11-30-2017 16:14
From: James Woidt
Subject: Interest in ASCE webinar short course - Bridge scour analysis

David,

   Terrific idea. I've frequently encountered these same topics when reviewing scour calculations. I'd argue the topic of scour is diverse, important, and frequently encountered enough to justify three separate sessions, perhaps an hour each. I could see the following series:

• Scour Primer: Overview of scour processes, types of scour, and primer of general scour equations including contraction scour, pressure scour, "bedform scour", bend scour, and/or general river scour. Perhaps a detailed discussion of contraction scour and general river scour as time allows.
• Focus on Pier Scour: including the topics you mentioned and a primer on available scour equations for special conditions (piers on erodible bedrock, cohesive materials, etc.)
• Focus on Other Types of Commonly-Encountered Scour: abutment, open-bottomed culverts, and perhaps simplified long-term degradation.

   I have a host of ideas that I could share with you on each of these topics off-line, but the most important one, and surprisingly the one I encounter most frequently, is to heed the model warnings about super-critical flow. It's important to note while sub-critical flow may be conservative for floodplain mapping, it is NOT conservative for some scour conditions (or stabilization design for that matter).

   -James


------------------------------
James Woidt A.M.ASCE
Woidt Engineering & Consulting, PC
Water Resources Engineer
Scarborough, ME
------------------------------


Original Message:
Sent: 11-30-2017 10:45
From: Cordie Qualle
Subject: Interest in ASCE webinar short course - Bridge scour analysis

David:

Thanks for sharing your experience with sour analysis errors.  I would be interested in your webinar.

------------------------------
Cordie Qualle P.E., M.ASCE
Industry Faculty Fellow
CSU Fresno
Fresno CA

​Another problem is that people assume that the worst scour depths occur due to the largest flow conditions.  I always teach to do a full range of flows and do the scour computations for each condition.  For instance, using HEC-RAS at just bank flow depth may give higher shear stress than for a higher flow condition that has water in the overbanks that re-distributes the total flow and decreases the flow in the main channel.

Another problem could be that a lower flow comes to an elongated pier at a worse flow angle than the higher design flow, resulting in more pier scour than previously thought.  If you have a 2-D model, this change in angle could easily checked.

So now I have a total of 9 potential scenarios to present related to mis-application of HEC-RAS for bridge scour analysis.  Again, I am open to suggestions for more problems that you can present to me for possible inclusion or substitution to the proposed ones.  I give credit for contributions of material to my presentations.

I have taught 2-3 day seminars for ASCE on HEC-RAS (and for FHWA) and Bridge scour analysis but they were separate and not integrated like what I am proposing.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

David - 

   Thanks for the information on ASCE's bridge scour webinar. Based on your description, I concur that it covers some of the "primer" topics I recommended. My idea for the multiple webinar topics stemmed from my observation that of the topics discussed in this thread, all but one is related to pier scour which appears to justify a webinar just for pier scour. I think similar webinars/list of topics could be generated for the application of HEC-RAS hydraulic design tool to estimate abutment and contraction scour, although probably together as one webinar. However, each of these topics could be expanded by including, in addition to a detailed discussion of the application of HEC-RAS, discussion of some readily-accessible scour equations presented in HEC-18 and other documents that are not embedded in HEC-RAS. HEC-RAS is useful for a lot of situations (with the proper setup as you've pointed out!), but I think it's also useful to present to practitioners that there exist these other scour equations for specific situations that may be more appropriate for specific situations. To your point, this can probably be a primer but I also think it's important to convey that scour science doesn't start and stop with HEC-RAS. No one is suggesting this, but personally, I've found a few slides on the limitations of the webinar topic and a pointer towards where more information exists to be one of the most useful parts of any webinar. 

   In response to your question, you have a very comprehensive list of frequently-encountered misapplications when using HEC-RAS to estimate scour. A few other thoughts that I can think of, focused on HEC-RAS itself: 

• Overview of the general limitations/applicability of the embedded pier scour equations.
• Understanding the limitations of your geotechnical data. As an example, I've seen D50s for the substrate determined from geotechnical borings. However, a 2" or 3" split spoon sampler isn't physically capable of measuring the coarser fraction of cobble-bed streams. The resulting D50 will be conservative, but the impact of this conservatism on the design and cost of protection measures and foundations should be considered (and perhaps justify the re-sampling of bed material via another method).
• On a similar line of thinking, verify that substrate data is consistent with the limitations of the equations - I've seen several submittals that input fine-sized D50s into the scour equations, whereas most of the equations were developed for non-cohesive materials. There are other equations for scour in fine materials.
• Consider the impact of varying geotechnical strata. A shallow, solid bedrock layer may restrict scour, whereas a layer of finer-grained materials that are exposed may increase scour (in comparison to the surface characteristics).
• Selection of the toe stations in the approach and abutment XS. HEC-RAS tends to not do a great job of projecting the abutment XS back to the approach XS, and this can really skew the Qe, Ae, etc., parameters.
• Selection of L' "length of live flow": HEC-18 has a good discussion on this, but it's subjective and can cause difficulties in some situations. The flow distribution output is helpful in selecting this and is useful to provide to reviewers to justify selection of L'. Proper setup of ineffective flow areas will make this much more straightforward, but that's a topic covered in other ASCE webinars.

   Hope this helps.

------------------------------
James Woidt A.M.ASCE
Water Resources Engineer
Scarborough ME
------------------------------

Original Message:
Sent: 11-30-2017 15:28
From: David Williams
Subject: Interest in ASCE webinar short course - Bridge scour analysis

​Another problem is that people assume that the worst scour depths occur due to the largest flow conditions.  I always teach to do a full range of flows and do the scour computations for each condition.  For instance, using HEC-RAS at just bank flow depth may give higher shear stress than for a higher flow condition that has water in the overbanks that re-distributes the total flow and decreases the flow in the main channel.

Another problem could be that a lower flow comes to an elongated pier at a worse flow angle than the higher design flow, resulting in more pier scour than previously thought.  If you have a 2-D model, this change in angle could easily checked.

So now I have a total of 9 potential scenarios to present related to mis-application of HEC-RAS for bridge scour analysis.  Again, I am open to suggestions for more problems that you can present to me for possible inclusion or substitution to the proposed ones.  I give credit for contributions of material to my presentations.

I have taught 2-3 day seminars for ASCE on HEC-RAS (and for FHWA) and Bridge scour analysis but they were separate and not integrated like what I am proposing.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

​James:

Thank you for your detailed input.  Per our suggestion, I will seriously consider putting some slides at the beginning stating that using HEC-RAS for bridge scour is not the end all.  Need to be aware of other scour equations (maybe show some that are not used in RAS) that may be more appropriate as well as the limitations of the ones that are in RAS. 

I had not thought of the possible error of the projection of the abutment toe to the adjacent cross section for abutment scour.  I need to give that some thought and come up with a way to present it.  Perhaps you can elaborate on it for me.

Your point about geotechnical information being representative is right on.  For instance, most geotechnical information for bridge scour studies were obtained with the bridge engineer in mind, not a water resources engineer.  One should make sure the sample(s) are representative of the river situation, not the info required to determine pier friction for burial!

David

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

Original Message:
Sent: 12-01-2017 09:50
From: James Woidt
Subject: Interest in ASCE webinar short course - Bridge scour analysis

David -

   Thanks for the information on ASCE's bridge scour webinar. Based on your description, I concur that it covers some of the "primer" topics I recommended. My idea for the multiple webinar topics stemmed from my observation that of the topics discussed in this thread, all but one is related to pier scour which appears to justify a webinar just for pier scour. I think similar webinars/list of topics could be generated for the application of HEC-RAS hydraulic design tool to estimate abutment and contraction scour, although probably together as one webinar. However, each of these topics could be expanded by including, in addition to a detailed discussion of the application of HEC-RAS, discussion of some readily-accessible scour equations presented in HEC-18 and other documents that are not embedded in HEC-RAS. HEC-RAS is useful for a lot of situations (with the proper setup as you've pointed out!), but I think it's also useful to present to practitioners that there exist these other scour equations for specific situations that may be more appropriate for specific situations. To your point, this can probably be a primer but I also think it's important to convey that scour science doesn't start and stop with HEC-RAS. No one is suggesting this, but personally, I've found a few slides on the limitations of the webinar topic and a pointer towards where more information exists to be one of the most useful parts of any webinar.

   In response to your question, you have a very comprehensive list of frequently-encountered misapplications when using HEC-RAS to estimate scour. A few other thoughts that I can think of, focused on HEC-RAS itself:

• Overview of the general limitations/applicability of the embedded pier scour equations.
• Understanding the limitations of your geotechnical data. As an example, I've seen D50s for the substrate determined from geotechnical borings. However, a 2" or 3" split spoon sampler isn't physically capable of measuring the coarser fraction of cobble-bed streams. The resulting D50 will be conservative, but the impact of this conservatism on the design and cost of protection measures and foundations should be considered (and perhaps justify the re-sampling of bed material via another method).
• On a similar line of thinking, verify that substrate data is consistent with the limitations of the equations - I've seen several submittals that input fine-sized D50s into the scour equations, whereas most of the equations were developed for non-cohesive materials. There are other equations for scour in fine materials.
• Consider the impact of varying geotechnical strata. A shallow, solid bedrock layer may restrict scour, whereas a layer of finer-grained materials that are exposed may increase scour (in comparison to the surface characteristics).
• Selection of the toe stations in the approach and abutment XS. HEC-RAS tends to not do a great job of projecting the abutment XS back to the approach XS, and this can really skew the Qe, Ae, etc., parameters.
• Selection of L' "length of live flow": HEC-18 has a good discussion on this, but it's subjective and can cause difficulties in some situations. The flow distribution output is helpful in selecting this and is useful to provide to reviewers to justify selection of L'. Proper setup of ineffective flow areas will make this much more straightforward, but that's a topic covered in other ASCE webinars.

   Hope this helps.

------------------------------
James Woidt A.M.ASCE
Water Resources Engineer
Scarborough ME
------------------------------


Original Message:
Sent: 11-30-2017 15:28
From: David Williams
Subject: Interest in ASCE webinar short course - Bridge scour analysis

​Another problem is that people assume that the worst scour depths occur due to the largest flow conditions.  I always teach to do a full range of flows and do the scour computations for each condition.  For instance, using HEC-RAS at just bank flow depth may give higher shear stress than for a higher flow condition that has water in the overbanks that re-distributes the total flow and decreases the flow in the main channel.

Another problem could be that a lower flow comes to an elongated pier at a worse flow angle than the higher design flow, resulting in more pier scour than previously thought.  If you have a 2-D model, this change in angle could easily checked.

So now I have a total of 9 potential scenarios to present related to mis-application of HEC-RAS for bridge scour analysis.  Again, I am open to suggestions for more problems that you can present to me for possible inclusion or substitution to the proposed ones.  I give credit for contributions of material to my presentations.

I have taught 2-3 day seminars for ASCE on HEC-RAS (and for FHWA) and Bridge scour analysis but they were separate and not integrated like what I am proposing.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO

​James:

If you want to discuss with me directly, please email me at david@....

David

------------------------------
David Williams Ph.D., P.E., D.WRE, HG, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

Original Message:
Sent: 12-01-2017 09:50
From: James Woidt
Subject: Interest in ASCE webinar short course - Bridge scour analysis

David -

   Thanks for the information on ASCE's bridge scour webinar. Based on your description, I concur that it covers some of the "primer" topics I recommended. My idea for the multiple webinar topics stemmed from my observation that of the topics discussed in this thread, all but one is related to pier scour which appears to justify a webinar just for pier scour. I think similar webinars/list of topics could be generated for the application of HEC-RAS hydraulic design tool to estimate abutment and contraction scour, although probably together as one webinar. However, each of these topics could be expanded by including, in addition to a detailed discussion of the application of HEC-RAS, discussion of some readily-accessible scour equations presented in HEC-18 and other documents that are not embedded in HEC-RAS. HEC-RAS is useful for a lot of situations (with the proper setup as you've pointed out!), but I think it's also useful to present to practitioners that there exist these other scour equations for specific situations that may be more appropriate for specific situations. To your point, this can probably be a primer but I also think it's important to convey that scour science doesn't start and stop with HEC-RAS. No one is suggesting this, but personally, I've found a few slides on the limitations of the webinar topic and a pointer towards where more information exists to be one of the most useful parts of any webinar.

   In response to your question, you have a very comprehensive list of frequently-encountered misapplications when using HEC-RAS to estimate scour. A few other thoughts that I can think of, focused on HEC-RAS itself:

• Overview of the general limitations/applicability of the embedded pier scour equations.
• Understanding the limitations of your geotechnical data. As an example, I've seen D50s for the substrate determined from geotechnical borings. However, a 2" or 3" split spoon sampler isn't physically capable of measuring the coarser fraction of cobble-bed streams. The resulting D50 will be conservative, but the impact of this conservatism on the design and cost of protection measures and foundations should be considered (and perhaps justify the re-sampling of bed material via another method).
• On a similar line of thinking, verify that substrate data is consistent with the limitations of the equations - I've seen several submittals that input fine-sized D50s into the scour equations, whereas most of the equations were developed for non-cohesive materials. There are other equations for scour in fine materials.
• Consider the impact of varying geotechnical strata. A shallow, solid bedrock layer may restrict scour, whereas a layer of finer-grained materials that are exposed may increase scour (in comparison to the surface characteristics).
• Selection of the toe stations in the approach and abutment XS. HEC-RAS tends to not do a great job of projecting the abutment XS back to the approach XS, and this can really skew the Qe, Ae, etc., parameters.
• Selection of L' "length of live flow": HEC-18 has a good discussion on this, but it's subjective and can cause difficulties in some situations. The flow distribution output is helpful in selecting this and is useful to provide to reviewers to justify selection of L'. Proper setup of ineffective flow areas will make this much more straightforward, but that's a topic covered in other ASCE webinars.

   Hope this helps.

------------------------------
James Woidt A.M.ASCE
Water Resources Engineer
Scarborough ME
------------------------------


Original Message:
Sent: 11-30-2017 15:28
From: David Williams
Subject: Interest in ASCE webinar short course - Bridge scour analysis

​Another problem is that people assume that the worst scour depths occur due to the largest flow conditions.  I always teach to do a full range of flows and do the scour computations for each condition.  For instance, using HEC-RAS at just bank flow depth may give higher shear stress than for a higher flow condition that has water in the overbanks that re-distributes the total flow and decreases the flow in the main channel.

Another problem could be that a lower flow comes to an elongated pier at a worse flow angle than the higher design flow, resulting in more pier scour than previously thought.  If you have a 2-D model, this change in angle could easily checked.

So now I have a total of 9 potential scenarios to present related to mis-application of HEC-RAS for bridge scour analysis.  Again, I am open to suggestions for more problems that you can present to me for possible inclusion or substitution to the proposed ones.  I give credit for contributions of material to my presentations.

I have taught 2-3 day seminars for ASCE on HEC-RAS (and for FHWA) and Bridge scour analysis but they were separate and not integrated like what I am proposing.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO

​James:

Thank you for your detailed input.  Per our suggestion, I will seriously consider putting some slides at the beginning stating that using HEC-RAS for bridge scour is not the end all.  Need to be aware of other scour equations (maybe show some that are not used in RAS) that may be more appropriate as well as the limitations of the ones that are in RAS.

I had not thought of the possible error of the projection of the abutment toe to the adjacent cross section for abutment scour.  I need to give that some thought and come up with a way to present it.  Perhaps you can elaborate on it for me.

Your point about geotechnical information being representative is right on.  For instance, most geotechnical information for bridge scour studies were obtained with the bridge engineer in mind, not a water resources engineer.  One should make sure the sample(s) are representative of the river situation, not the info required to determine pier friction for burial!

David

------------------------------
David Williams Ph.D., P.E., D.WRE, HG, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

Original Message:
Sent: 12-01-2017 09:50
From: James Woidt
Subject: Interest in ASCE webinar short course - Bridge scour analysis

David -

   Thanks for the information on ASCE's bridge scour webinar. Based on your description, I concur that it covers some of the "primer" topics I recommended. My idea for the multiple webinar topics stemmed from my observation that of the topics discussed in this thread, all but one is related to pier scour which appears to justify a webinar just for pier scour. I think similar webinars/list of topics could be generated for the application of HEC-RAS hydraulic design tool to estimate abutment and contraction scour, although probably together as one webinar. However, each of these topics could be expanded by including, in addition to a detailed discussion of the application of HEC-RAS, discussion of some readily-accessible scour equations presented in HEC-18 and other documents that are not embedded in HEC-RAS. HEC-RAS is useful for a lot of situations (with the proper setup as you've pointed out!), but I think it's also useful to present to practitioners that there exist these other scour equations for specific situations that may be more appropriate for specific situations. To your point, this can probably be a primer but I also think it's important to convey that scour science doesn't start and stop with HEC-RAS. No one is suggesting this, but personally, I've found a few slides on the limitations of the webinar topic and a pointer towards where more information exists to be one of the most useful parts of any webinar.

   In response to your question, you have a very comprehensive list of frequently-encountered misapplications when using HEC-RAS to estimate scour. A few other thoughts that I can think of, focused on HEC-RAS itself:

• Overview of the general limitations/applicability of the embedded pier scour equations.
• Understanding the limitations of your geotechnical data. As an example, I've seen D50s for the substrate determined from geotechnical borings. However, a 2" or 3" split spoon sampler isn't physically capable of measuring the coarser fraction of cobble-bed streams. The resulting D50 will be conservative, but the impact of this conservatism on the design and cost of protection measures and foundations should be considered (and perhaps justify the re-sampling of bed material via another method).
• On a similar line of thinking, verify that substrate data is consistent with the limitations of the equations - I've seen several submittals that input fine-sized D50s into the scour equations, whereas most of the equations were developed for non-cohesive materials. There are other equations for scour in fine materials.
• Consider the impact of varying geotechnical strata. A shallow, solid bedrock layer may restrict scour, whereas a layer of finer-grained materials that are exposed may increase scour (in comparison to the surface characteristics).
• Selection of the toe stations in the approach and abutment XS. HEC-RAS tends to not do a great job of projecting the abutment XS back to the approach XS, and this can really skew the Qe, Ae, etc., parameters.
• Selection of L' "length of live flow": HEC-18 has a good discussion on this, but it's subjective and can cause difficulties in some situations. The flow distribution output is helpful in selecting this and is useful to provide to reviewers to justify selection of L'. Proper setup of ineffective flow areas will make this much more straightforward, but that's a topic covered in other ASCE webinars.

   Hope this helps.

------------------------------
James Woidt A.M.ASCE
Water Resources Engineer
Scarborough ME
------------------------------


Original Message:
Sent: 11-30-2017 15:28
From: David Williams
Subject: Interest in ASCE webinar short course - Bridge scour analysis

​Another problem is that people assume that the worst scour depths occur due to the largest flow conditions.  I always teach to do a full range of flows and do the scour computations for each condition.  For instance, using HEC-RAS at just bank flow depth may give higher shear stress than for a higher flow condition that has water in the overbanks that re-distributes the total flow and decreases the flow in the main channel.

Another problem could be that a lower flow comes to an elongated pier at a worse flow angle than the higher design flow, resulting in more pier scour than previously thought.  If you have a 2-D model, this change in angle could easily checked.

So now I have a total of 9 potential scenarios to present related to mis-application of HEC-RAS for bridge scour analysis.  Again, I am open to suggestions for more problems that you can present to me for possible inclusion or substitution to the proposed ones.  I give credit for contributions of material to my presentations.

I have taught 2-3 day seminars for ASCE on HEC-RAS (and for FHWA) and Bridge scour analysis but they were separate and not integrated like what I am proposing.

------------------------------
David Williams Ph.D., P.E., D.WRE, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO

Great thread!  I have some general recommendations that are probably not going to result in anything...but nonetheless...

1. ​There should be a series of several ~30 to 45 minute recorded sessions that a user could watch at their own time.  For professionals, having to attend a 1.5h webinar at a specific time can be onerous because of various hoops that we have to jump through.  Having pre-recorded (free) sessions would be great so that the user can watch them on their own time at lunch as their schedule permits without having to obtain permission or organize a luncheon for everyone at the company that might be interested in the topic.
2. In addition to a series of videos on scour analysis, there should be a series on scour countermeasures.
3. There should be a certification that is required to perform scour analysis.  Scour is the largest cause of bridge failure.  It is important that the calculations (and the programs used to perform the calculations) are performed properly.  There is enough uncertainty and risk involved with the variables used to calculate the depth of scour that we don't need to introduce any additional uncertainty and risk by not performing the calculations properly.  Some might argue that having a PE is the certification...but I think that this is a little bit specialized and state DOTs should require PEs to have special scour certification in order to submit a scour analysis.

------------------------------
Jennifer Morreale P.E., CFM, M.ASCE
Project Engineer
Hubbell Roth & Clark
Detroit MI
------------------------------

​Jennifer:

Thank you for your input.  For webinars, ASCE does not have any less than 1 hour long.  Also, for those that have time constraints, they can, for a fee, have access to the recorded webinar of which I believe they can watch and listen at their leisure.

David

------------------------------
David Williams Ph.D., P.E., D.WRE, HG, F.EWRI, F.ASCE
David T. Williams and Assoc.
Commerce City CO
------------------------------

Original Message:
Sent: 12-05-2017 07:39
From: Jennifer Morreale
Subject: Interest in ASCE webinar short course - Bridge scour analysis

Great thread!  I have some general recommendations that are probably not going to result in anything...but nonetheless...

1. ​There should be a series of several ~30 to 45 minute recorded sessions that a user could watch at their own time.  For professionals, having to attend a 1.5h webinar at a specific time can be onerous because of various hoops that we have to jump through.  Having pre-recorded (free) sessions would be great so that the user can watch them on their own time at lunch as their schedule permits without having to obtain permission or organize a luncheon for everyone at the company that might be interested in the topic.
2. In addition to a series of videos on scour analysis, there should be a series on scour countermeasures.
3. There should be a certification that is required to perform scour analysis.  Scour is the largest cause of bridge failure.  It is important that the calculations (and the programs used to perform the calculations) are performed properly.  There is enough uncertainty and risk involved with the variables used to calculate the depth of scour that we don't need to introduce any additional uncertainty and risk by not performing the calculations properly.  Some might argue that having a PE is the certification...but I think that this is a little bit specialized and state DOTs should require PEs to have special scour certification in order to submit a scour analysis.

------------------------------
Jennifer Morreale P.E., CFM, M.ASCE
Project Engineer
Hubbell Roth & Clark
Detroit MI
------------------------------