Discussion: View Thread

​​Good Morning and Happy Thanksgiving everyone!
In Maryland it is typical to place geotextile cloth along a channel before placing riprap.  I have been informed that this is to prevent the migration of fine sediment along the channel invert.
Does anyone know of any studies that have been undertaken to determine the rate of sediment transport in lined vs unlined channels?  Does the geotextile actually prevent material from being eroded away from a channel?
Thank you!

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Armand De Rosset A.M.ASCE

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my understanding is that the riprap actually sinks into the bed material as the soil erodes without the geotextrile.

------------------------------
James Gracie Aff.M.ASCE
PRESIDENT
Brightwater Inc
College Park MD
------------------------------

Original Message:
Sent: 11-22-2017 11:07
From: Armand De Rosset
Subject: Geotextile and Fines Migration

​​Good Morning and Happy Thanksgiving everyone!
In Maryland it is typical to place geotextile cloth along a channel before placing riprap.  I have been informed that this is to prevent the migration of fine sediment along the channel invert.
Does anyone know of any studies that have been undertaken to determine the rate of sediment transport in lined vs unlined channels?  Does the geotextile actually prevent material from being eroded away from a channel?
Thank you!

------------------------------
Armand De Rosset A.M.ASCE

------------------------------

I believe that the issue is not that simple regarding erosion of the sediment. Erosion or conversely, deposition of sediment within a flowing water course depends on numerous factors including the velocity of flow and the existing bedload and suspended load of sediment in the flowing water.

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J Donald Houser P.E., M.ASCE
Cons Engr
Long Beach CA
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Original Message:
Sent: 11-24-2017 23:01
From: James Gracie
Subject: Geotextile and Fines Migration

my understanding is that the riprap actually sinks into the bed material as the soil erodes without the geotextrile.

------------------------------
James Gracie Aff.M.ASCE
PRESIDENT
Brightwater Inc
College Park MD

Original Message:
Sent: 11-22-2017 11:07
From: Armand De Rosset
Subject: Geotextile and Fines Migration

​​Good Morning and Happy Thanksgiving everyone!
In Maryland it is typical to place geotextile cloth along a channel before placing riprap.  I have been informed that this is to prevent the migration of fine sediment along the channel invert.
Does anyone know of any studies that have been undertaken to determine the rate of sediment transport in lined vs unlined channels?  Does the geotextile actually prevent material from being eroded away from a channel?
Thank you!

------------------------------
Armand De Rosset A.M.ASCE

------------------------------

​James:

If there is no filter (geotextiles or granular) under the riprap and the underlying material is composed of non-cohesive material, then yes, the hydraulic turbulence would "suck" the material from under the riprap and the riprap would settle to fill the voids.  However, this is not desirable because it could possibly produce a very irregular surface that would create additional turbulence that would exceed the design conditions of the riprap.  Also, the settlement could cause local increases/decreases in bank slopes that would cause riprap failure due to exceeding the riprap angle of repose or due to geotechnical limitations of the bank slope.  The differential settling of the riprap would also cause separation of the riprap layer resulting in exposure of the underlying material.  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: 11-24-2017 23:01
From: James Gracie
Subject: Geotextile and Fines Migration

my understanding is that the riprap actually sinks into the bed material as the soil erodes without the geotextrile.

------------------------------
James Gracie Aff.M.ASCE
PRESIDENT
Brightwater Inc
College Park MD

Original Message:
Sent: 11-22-2017 11:07
From: Armand De Rosset
Subject: Geotextile and Fines Migration

​​Good Morning and Happy Thanksgiving everyone!
In Maryland it is typical to place geotextile cloth along a channel before placing riprap.  I have been informed that this is to prevent the migration of fine sediment along the channel invert.
Does anyone know of any studies that have been undertaken to determine the rate of sediment transport in lined vs unlined channels?  Does the geotextile actually prevent material from being eroded away from a channel?
Thank you!

------------------------------
Armand De Rosset A.M.ASCE

------------------------------

​The rate of sediment migration through geotextiles under riprap depends on the sediment gradation, riprap gradation, riprap angularity, size of openings of the geotextiles, height of the riprap drop during installation, the turbulence above the riprap, woven or non-woven geotextiles, wave actions or rivers, and many other conditions.  I have been in the riprap business a long time and do not recall studies of the rate of sediment migration under a variety of such conditions.  Most studies are related to the proper geotextile and its openings and the underlying material underneath them for limited combinations.  If the proper geotextiles are determines, the sediment migration rate should be negligible.  The most commonly used document for design is HEC-11.  https://www.fhwa.dot.gov/engineering/hydraulics/pubs/hec/hec11sI.pdf

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

Original Message:
Sent: 11-22-2017 11:07
From: Armand De Rosset
Subject: Geotextile and Fines Migration

​​Good Morning and Happy Thanksgiving everyone!
In Maryland it is typical to place geotextile cloth along a channel before placing riprap.  I have been informed that this is to prevent the migration of fine sediment along the channel invert.
Does anyone know of any studies that have been undertaken to determine the rate of sediment transport in lined vs unlined channels?  Does the geotextile actually prevent material from being eroded away from a channel?
Thank you!

------------------------------
Armand De Rosset A.M.ASCE

------------------------------

​The purpose of the geotextile is not specifically to prevent the sediment from erosion, though it is a part of the erosion protection system.  Rip rap requires interlocking of the rocks and open pore space to dissipate the energy of the flow.  If the rip rap becomes clogged with fines, it reduces its ability for energy dissipation.  If the rock is sinking into soft sediment, the rocks separate and lose the interlock making them more susceptible to being dislodged.  Of course, sediments are eroded when this happens.  An important consideration in geotextile filter design is the clogging of the geotextile, since pore pressures can become elevated beneath a clogged textile resulting in failure of the rip rap.  There is really no controversy on whether a filter is required beneath rip rap.  Check out the NHCRP report on rip rap design at :  http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_568.pdf This document contains an excellent discussion of rip rap design including the filter requirements.

------------------------------
Michael Byle P.E., D.GE, F.ASCE
Tetra Tech Inc.,
Langhorne PA
------------------------------

Original Message:
Sent: 11-22-2017 11:07
From: Armand De Rosset
Subject: Geotextile and Fines Migration

​​Good Morning and Happy Thanksgiving everyone!
In Maryland it is typical to place geotextile cloth along a channel before placing riprap.  I have been informed that this is to prevent the migration of fine sediment along the channel invert.
Does anyone know of any studies that have been undertaken to determine the rate of sediment transport in lined vs unlined channels?  Does the geotextile actually prevent material from being eroded away from a channel?
Thank you!

------------------------------
Armand De Rosset A.M.ASCE

------------------------------

I prefer a granular filter to geotextile. The issues I have seen with geotextile are that the rocks actually slide down the face of the fabric and eventually the fabric can get exposed creating poor aesthetics and a compromised system. I think the granular filter offers more flexibility to adjustment and is a more natural approach. Also could be better for water quality.

------------------------------
Brett Jordan P.E.,PhD, M.ASCE
Hydrogeo Designs LLC
Houston TX
------------------------------

Original Message:
Sent: 11-27-2017 07:25
From: Michael Byle
Subject: Geotextile and Fines Migration

​The purpose of the geotextile is not specifically to prevent the sediment from erosion, though it is a part of the erosion protection system.  Rip rap requires interlocking of the rocks and open pore space to dissipate the energy of the flow.  If the rip rap becomes clogged with fines, it reduces its ability for energy dissipation.  If the rock is sinking into soft sediment, the rocks separate and lose the interlock making them more susceptible to being dislodged.  Of course, sediments are eroded when this happens.  An important consideration in geotextile filter design is the clogging of the geotextile, since pore pressures can become elevated beneath a clogged textile resulting in failure of the rip rap.  There is really no controversy on whether a filter is required beneath rip rap.  Check out the NHCRP report on rip rap design at :  http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_568.pdf This document contains an excellent discussion of rip rap design including the filter requirements.

------------------------------
Michael Byle P.E., D.GE, F.ASCE
Tetra Tech Inc.,
Langhorne PA

Original Message:
Sent: 11-22-2017 11:07
From: Armand De Rosset
Subject: Geotextile and Fines Migration

​​Good Morning and Happy Thanksgiving everyone!
In Maryland it is typical to place geotextile cloth along a channel before placing riprap.  I have been informed that this is to prevent the migration of fine sediment along the channel invert.
Does anyone know of any studies that have been undertaken to determine the rate of sediment transport in lined vs unlined channels?  Does the geotextile actually prevent material from being eroded away from a channel?
Thank you!

------------------------------
Armand De Rosset A.M.ASCE

------------------------------

​Dr. Jordan:  I too rather use granular filters rather than geotextiles.  Dropping and rolling of the riprap can cause tears in the fabric that would compromise the design.  Also, granular composition will last much longer than fabric which can become brittle and lose strength over time.

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

Original Message:
Sent: 11-28-2017 08:29
From: Brett Jordan
Subject: Geotextile and Fines Migration

I prefer a granular filter to geotextile. The issues I have seen with geotextile are that the rocks actually slide down the face of the fabric and eventually the fabric can get exposed creating poor aesthetics and a compromised system. I think the granular filter offers more flexibility to adjustment and is a more natural approach. Also could be better for water quality.

------------------------------
Brett Jordan P.E.,PhD, M.ASCE
Hydrogeo Designs LLC
Houston TX

Original Message:
Sent: 11-27-2017 07:25
From: Michael Byle
Subject: Geotextile and Fines Migration

​The purpose of the geotextile is not specifically to prevent the sediment from erosion, though it is a part of the erosion protection system.  Rip rap requires interlocking of the rocks and open pore space to dissipate the energy of the flow.  If the rip rap becomes clogged with fines, it reduces its ability for energy dissipation.  If the rock is sinking into soft sediment, the rocks separate and lose the interlock making them more susceptible to being dislodged.  Of course, sediments are eroded when this happens.  An important consideration in geotextile filter design is the clogging of the geotextile, since pore pressures can become elevated beneath a clogged textile resulting in failure of the rip rap.  There is really no controversy on whether a filter is required beneath rip rap.  Check out the NHCRP report on rip rap design at :  http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_568.pdf This document contains an excellent discussion of rip rap design including the filter requirements.

------------------------------
Michael Byle P.E., D.GE, F.ASCE
Tetra Tech Inc.,
Langhorne PA

Original Message:
Sent: 11-22-2017 11:07
From: Armand De Rosset
Subject: Geotextile and Fines Migration

​​Good Morning and Happy Thanksgiving everyone!
In Maryland it is typical to place geotextile cloth along a channel before placing riprap.  I have been informed that this is to prevent the migration of fine sediment along the channel invert.
Does anyone know of any studies that have been undertaken to determine the rate of sediment transport in lined vs unlined channels?  Does the geotextile actually prevent material from being eroded away from a channel?
Thank you!

------------------------------
Armand De Rosset A.M.ASCE

------------------------------

http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_568.pdf

------------------------------
Rebecca Stack A.M.ASCE
Principal
Washington DC
------------------------------

Original Message:
Sent: 11-28-2017 14:54
From: David Williams
Subject: Geotextile and Fines Migration

​Dr. Jordan:  I too rather use granular filters rather than geotextiles.  Dropping and rolling of the riprap can cause tears in the fabric that would compromise the design.  Also, granular composition will last much longer than fabric which can become brittle and lose strength over time.

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

Original Message:
Sent: 11-28-2017 08:29
From: Brett Jordan
Subject: Geotextile and Fines Migration

I prefer a granular filter to geotextile. The issues I have seen with geotextile are that the rocks actually slide down the face of the fabric and eventually the fabric can get exposed creating poor aesthetics and a compromised system. I think the granular filter offers more flexibility to adjustment and is a more natural approach. Also could be better for water quality.

------------------------------
Brett Jordan P.E.,PhD, M.ASCE
Hydrogeo Designs LLC
Houston TX

Original Message:
Sent: 11-27-2017 07:25
From: Michael Byle
Subject: Geotextile and Fines Migration

​The purpose of the geotextile is not specifically to prevent the sediment from erosion, though it is a part of the erosion protection system.  Rip rap requires interlocking of the rocks and open pore space to dissipate the energy of the flow.  If the rip rap becomes clogged with fines, it reduces its ability for energy dissipation.  If the rock is sinking into soft sediment, the rocks separate and lose the interlock making them more susceptible to being dislodged.  Of course, sediments are eroded when this happens.  An important consideration in geotextile filter design is the clogging of the geotextile, since pore pressures can become elevated beneath a clogged textile resulting in failure of the rip rap.  There is really no controversy on whether a filter is required beneath rip rap.  Check out the NHCRP report on rip rap design at :  http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_568.pdf This document contains an excellent discussion of rip rap design including the filter requirements.

------------------------------
Michael Byle P.E., D.GE, F.ASCE
Tetra Tech Inc.,
Langhorne PA

Original Message:
Sent: 11-22-2017 11:07
From: Armand De Rosset
Subject: Geotextile and Fines Migration

​​Good Morning and Happy Thanksgiving everyone!
In Maryland it is typical to place geotextile cloth along a channel before placing riprap.  I have been informed that this is to prevent the migration of fine sediment along the channel invert.
Does anyone know of any studies that have been undertaken to determine the rate of sediment transport in lined vs unlined channels?  Does the geotextile actually prevent material from being eroded away from a channel?
Thank you!

------------------------------
Armand De Rosset A.M.ASCE

------------------------------

Armand,

There is a technical book called Designing With Geosynthetics 4th Edition by Robert M. Koerner. Chapter two within this book is titled Designing with Geotextiles and it is a good reference for this type of question. Section 2.2.3 Filtration specifically and then the subheading Soil Retention on page 85 will lead you best to a solution. Though there are many factors that will effect the rate of sediment transport in lined channels (as stated in previous replies); some natural (i.e. river flow rate) and some unnatural. For the unnatural factors many of them are a result of the initial geotextile chosen and the void space associated with that specific filter fabric. If the void spaces in the geotextile are too large soil piping can be caused which will accelerate the process of the soil structure beneath the riprap collapsing. To prevent this, it is the coarser soil fraction that must be intentionally retained and that is the targeted soil size in the design process. The coarser-sized particles eventually block the finer-sized particles and build up a stable upstream soil structure. 

To answer your question, Yes absolutely the geotextile will prevent material from being eroded away. Also for design purposes, it is recommended that 4-6 inches of about three-quarter inch stone be placed on top of the geotextile prior to the installation of the riprap. This will provide a solid base for the riprap, further prevent erosion, protect the geotextile from damage, and provide stability.

I am not aware of any studies between lined vs unlined channels and the rate of sediment transport. 

Best,
Darrell

------------------------------
Darrell Kennedy EIT, A.M.ASCE
Environmental Engineer-in-Training, Remediation, Environment
AECOM
Boston MA
------------------------------

Original Message:
Sent: 11-22-2017 11:07
From: Armand De Rosset
Subject: Geotextile and Fines Migration

​​Good Morning and Happy Thanksgiving everyone!
In Maryland it is typical to place geotextile cloth along a channel before placing riprap.  I have been informed that this is to prevent the migration of fine sediment along the channel invert.
Does anyone know of any studies that have been undertaken to determine the rate of sediment transport in lined vs unlined channels?  Does the geotextile actually prevent material from being eroded away from a channel?
Thank you!

------------------------------
Armand De Rosset A.M.ASCE

------------------------------