SWMM-USERS Digest - 17 May 2012 to 29 May 2012 (#2012-50)

[SWMM-USERS automatic digest system]

There are 12 messages totaling 1464 lines in this issue.

Topics of the day:

1. PSD and TSS (9)
2. Bio-retention cell surface slope (3)

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Date: Mon, 28 May 2012 23:59:58 -0400
From: Rishon Richard <rishon....@RYERSON.CA>
Subject: PSD and TSS

Hello,

Given the Particle Size Distribution for TSS in a subcatchment, what is the most efficient method of modelling the removal/treatment of TSS in a pond in SWMM 5?

Other threads have mentioned that the TSS PSD can be broken down by settling velocity characteristics. Does this mean that different buildup/washoff values need to be used for each TSS size group? Also, can someone please suggest a suitable treatment equation for TSS in a wet pond? I'm not sure if this thread was resolved: http://www.chiwater.com/BBS/forums/thread-view.asp?tid=2796&start=1

Thank you,

Rishon Richard
Graduate Student in Enviro. Applied Science and Management
Ryerson University, Toronto

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Date: Mon, 28 May 2012 22:19:31 -0600
From: Robert Dickinson <Robert.E....@INNOVYZE.COM>
Subject: Re: PSD and TSS

Hi Rishon,

Does this mean that different buildup/washoff values need to be used for each TSS size group? Yes, you will have to have a different washoff value (Event mean concentration or EMC) value for each particle size but you can do without the buildup values if you just interested in the particle size removal in the wet pond. Each particle size range is considered a pollutant.

A treatment expression for each particle size as a function of hydraulic residence time or depth might help you in your modeling. I am sure that you will get a lot of suggestions for removal equations from this posting.

Robert Dickinson
Innovyze Inc.
9340 Pontiac Drive                Tel:     813-712-0664
Tampa, Florida USA 33626       
robert.d...@innovyze.com
www.innovyze.com


-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Rishon Richard
Sent: Tuesday, May 29, 2012 12:00 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: [SWMM-USERS] PSD and TSS

Hello,

Given the Particle Size Distribution for TSS in a subcatchment, what is the most efficient method of modelling the removal/treatment of TSS in a pond in SWMM 5?

Other threads have mentioned that the TSS PSD can be broken down by settling velocity characteristics. Does this mean that different buildup/washoff values need to be used for each TSS size group? Also, can someone please suggest a suitable treatment equation for TSS in a wet pond? I'm not sure if this thread was resolved: http://www.chiwater.com/BBS/forums/thread-view.asp?tid=2796&start=1

Thank you,

Rishon Richard
Graduate Student in Enviro. Applied Science and Management Ryerson University, Toronto

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

Date: Tue, 29 May 2012 01:56:29 -0400
From: Rishon Richard <rishon....@RYERSON.CA>
Subject: Re: PSD and TSS

Thank you for the quick reply. Does this also apply to the exponential buildup/washoff functions? And if different values are required, where might I be able to find them or how might I go about calculating them?

----- Original Message -----
From: Robert Dickinson <Robert.E....@INNOVYZE.COM>
Date: Tuesday, May 29, 2012 12:19 am
Subject: Re: [SWMM-USERS] PSD and TSS
To: SWMM-...@LISTSERV.UOGUELPH.CA


> Hi Rishon,
>
> Does this mean that different buildup/washoff values need to be used
> for each TSS size group? Yes, you will have to have a different
> washoff value (Event mean concentration or EMC) value for each
> particle size but you can do without the buildup values if you just
> interested in the particle size removal in the wet pond. Each
> particle size range is considered a pollutant.
>
> A treatment expression for each particle size as a function of
> hydraulic residence time or depth might help you in your modeling. I
> am sure that you will get a lot of suggestions for removal equations
> from this posting.
>
> Robert Dickinson
> Innovyze Inc.
> 9340 Pontiac Drive                Tel:     813-712-0664
> Tampa, Florida USA 33626       
> robert.d...@innovyze.com
> www.innovyze.com
>
>
> -----Original Message-----
> From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
> Rishon Richard
> Sent: Tuesday, May 29, 2012 12:00 AM
> To: SWMM-...@LISTSERV.UOGUELPH.CA
> Subject: [SWMM-USERS] PSD and TSS
>
> Hello,
>
> Given the Particle Size Distribution for TSS in a subcatchment, what
> is the most efficient method of modelling the removal/treatment of TSS
> in a pond in SWMM 5?
>
> Other threads have mentioned that the TSS PSD can be broken down by
> settling velocity characteristics. Does this mean that different
> buildup/washoff values need to be used for each TSS size group? Also,
> can someone please suggest a suitable treatment equation for TSS in a
> wet pond? I'm not sure if this thread was resolved: http://www.chiwater.com/BBS/forums/thread-view.asp?tid=2796&start=1
>
> Thank you,
>
> Rishon Richard
> Graduate Student in Enviro. Applied Science and Management Ryerson
> University, Toronto
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
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>
> **********************************************************
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------------------------------

Date: Tue, 29 May 2012 15:17:52 +0300
From: Gerald Krebs <gerald...@AALTO.FI>
Subject: Bio-retention cell surface slope

I'm planning to model green roof scenarios for roofs between 2-20% slopes.
I'm planning to use the SWMM 5.0 LID Control option. The bio-retention cell
covers 100% of the subcatchment area which is the roof itself. Sample roofs
are 200m2. There were two questions coming up:



1) The LID Control Editor allows the definition of a surface slope. How
is it related to the actual roof slope? If I use the cell on a 10% sloped
roof, shall the cell surface slope be also 10%, or does it consider the
subcatchment slope. Varying the bio-retention slope didn't have any effect
neither on the water balance nor the peak flow and time. Shouldn't there be
an influence of the slope?

2) I tried bio-retention cells for several roofs (so far just using the
SWMM defaults) and the total runoff over some seven storms reduces to half.
However, there seem to be strange peaks in the LID runoff. The conventional
roof responds to every rain input (0.2mm) prompt, the green roof responds
only after a certain rain depth occurred. That I understand, but if the
green roof generates a peak, it's considerably higher than the conventional
roof induced peak. What is the reason for that?



Thanks,

Gerald


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Date: Tue, 29 May 2012 08:45:40 -0400
From: Lewis Rossman <Rossma...@EPAMAIL.EPA.GOV>
Subject: Re: Bio-retention cell surface slope

Gerald,

The LID slope for your green roof should be the slope of the roof
surface over which excess
rainfall runs off into the roof drains. However, the slope (and
roughness) will only be
taken into account if you provide a non-zero value for the Top Width of
Overland Flow
parameter in the LID Usage Editor (the form used to actually size the
green roof). Otherwise
any excess rainfall will simply runoff the roof instantaneously. This
width should be the
same as you used for your conventional roof.

I can't explain the higher peak flow for the green roof compared to the
conventional roof.
Perhaps it has something to do with the contribution from the underdrain
system. By the way,
we are currently redesigning the underdrain system for a green roof in
the LID module to
make it behave more like the drainage mats used for these systems rather
than the slotted
pipes used in non-roof bio-retention cells. I can't say when this update
will be ready.
--------------------------------------------------------------------------------------


Lewis Rossman
Environmental Scientist
Water Supply and Water Resources Division
U.S Environmental Protection Agency
email: rossma...@epa.gov

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Date: Tue, 29 May 2012 16:51:59 +0300
From: Gerald Krebs <gerald...@AALTO.FI>
Subject: Re: Bio-retention cell surface slope

Thanks for the advice Lewis,

I used four identical roofs (200m2) and I have a top flow width of 20m. They
only differ in the slope (2, 5, 15, and 20%). I connected for LID cells,
identical except the slope the same as in the associated roof. The
conventional roofs behave as expected (increasing peak and runoff volume
with increasing slope). However, if I connect the green roofs, all four
roofs behave exactly the same (I posted the status report sections below).

I used a underdrain coefficient of 0 (the default).

NO LID:

***************************
Subcatchment Runoff Summary
***************************


----------------------------------------------------------------------------
----------------------------
Total Total Total Total
Total Total Peak Runoff
Precip Runon Evap Infil
Runoff Runoff Runoff Coeff
Subcatchment mm mm mm mm
mm 10^6 ltr LPS

----------------------------------------------------------------------------
----------------------------
ROOF2 77.88 0.00 13.52 0.00
64.32 0.01 2.19 0.826
ROOF5 77.88 0.00 13.40 0.00
64.45 0.01 2.23 0.828
ROOF15 77.88 0.00 13.28 0.00
64.58 0.01 2.24 0.829
ROOF20 77.88 0.00 13.25 0.00
64.61 0.01 2.25 0.830
____________________________________________________________________________
_________

WITH LID:

***************************
Subcatchment Runoff Summary
***************************


----------------------------------------------------------------------------
----------------------------
Total Total Total Total
Total Total Peak Runoff
Precip Runon Evap Infil
Runoff Runoff Runoff Coeff
Subcatchment mm mm mm mm
mm 10^6 ltr LPS

----------------------------------------------------------------------------
----------------------------
ROOF2 77.88 0.00 31.02 4.62
37.27 0.01 2.22 0.478
ROOF5 77.88 0.00 31.02 4.62
37.27 0.01 2.22 0.478
ROOF15 77.88 0.00 31.02 4.62
37.27 0.01 2.22 0.478
ROOF20 77.88 0.00 31.02 4.62
37.27 0.01 2.22 0.478


***********************
LID Performance Summary
***********************


----------------------------------------------------------------------------
--------------------------------------
Total Evap Infil Surface
Drain Init. Final Pcnt.
Inflow Loss Loss Outflow
Outflow Storage Storage Error
Subcatchment LID Control mm mm mm mm
mm mm mm

----------------------------------------------------------------------------
--------------------------------------
ROOF2 GR_2 77.88 31.02 4.62 37.27
0.00 0.00 6.02 -1.35
ROOF5 GR_5 77.88 31.02 4.62 37.27
0.00 0.00 6.02 -1.35
ROOF15 GR_15 77.88 31.02 4.62 37.27
0.00 0.00 6.02 -1.35
ROOF20 GR_50 77.88 31.02 4.62 37.27
0.00 0.00 6.02 -1.35


Thanks,
Gerald


-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Lewis
Rossman
Sent: Tuesday, May 29, 2012 15:46
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] Bio-retention cell surface slope

Gerald,

The LID slope for your green roof should be the slope of the roof surface
over which excess rainfall runs off into the roof drains. However, the slope
(and
roughness) will only be
taken into account if you provide a non-zero value for the Top Width of
Overland Flow parameter in the LID Usage Editor (the form used to actually
size the green roof). Otherwise any excess rainfall will simply runoff the
roof instantaneously. This width should be the same as you used for your
conventional roof.

I can't explain the higher peak flow for the green roof compared to the
conventional roof.
Perhaps it has something to do with the contribution from the underdrain
system. By the way, we are currently redesigning the underdrain system for a
green roof in the LID module to make it behave more like the drainage mats
used for these systems rather than the slotted pipes used in non-roof
bio-retention cells. I can't say when this update will be ready.
----------------------------------------------------------------------------
----------


Lewis Rossman
Environmental Scientist
Water Supply and Water Resources Division U.S Environmental Protection
Agency
email: rossma...@epa.gov

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

Date: Tue, 29 May 2012 13:52:01 +0000
From: "Gregory, Mike (Canada)" <Mike.G...@AECOM.COM>
Subject: Re: PSD and TSS

I've been setting up my TSS models for pond design using Bob's suggestion (i.e., each TSS size fraction is represented as a separate pollutant). Treatment expressions are based on depth according to NURP size fractions & settling velocities (pg 33 of EPA-440-5-87-001). For example with the smallest 20% fraction (0.03 ft/hr average settling velocity according to NURP, and note that SWMM needs ft/s)...
If residual of say 25 mg/l, then: C = 25 + (TSS_1-25) * EXP(-0.00000833/DEPTH*DT)
If no residual then simply: C = TSS_1 * EXP(-0.00000833/DEPTH*DT)

I'm not smart enough to know the difference between exponential & other functions with SWMM water quality, but for TSS I just use the power function normalized by area with max buildup rates and washoff EMCs that vary by surface cover type (higher TSS for the urban/agriculture land uses, and lower TSS for the vegetated/natural areas). The power rate constant is a very sensitive parameter for TSS loading and I generally adjust this for each project so that I end up with unit loading rates from 500 kg/ha/yr (450 lb/ac/yr) to 2000 kg/ha/yr (1800 lb/ac/yr), depending on land use/imperviousness upstream of the pond, using an average year continuous simulation. I'd be ashamed to call this "calibration" - real monitoring results would be greatly welcomed (using sampling that distinguishes the surface washload PSD from the pond outlet PSD - these differ by an order of magnitude!).

Average annual TSS removal efficiency results for recent pond designs using this methodology (7 big urban ponds) range from 62% to 87% for the smallest 0-20% fraction (equiv 3 micron diameter particles and less), and from 95% to 100% for the middlest 40-60% fraction (7-17um). The biggest 80-100% fraction (>35um) almost always settles out in the pond quite quickly. Overall removal (all size fractions combined) has been 88% to 97% which exceeds our local presumptive design criteria for TSS in wet ponds. Of course, this diminishes greatly as the pond ages and loads up on settled particles. Reminder to use the dry bulk densities for each size fraction (accounting for organics/metals as necessary) when using model results to estimate accumulated pond sediment volumes for future dredge scheduling.


Regards,
mike g.

Michael A. Gregory, P.Eng., P.E.
AECOM - Kitchener, Canada

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Rishon Richard
Sent: Tuesday, May 29, 2012 1:56 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Thank you for the quick reply. Does this also apply to the exponential buildup/washoff functions? And if different values are required, where might I be able to find them or how might I go about calculating them?

----- Original Message -----
From: Robert Dickinson <Robert.E....@INNOVYZE.COM>
Date: Tuesday, May 29, 2012 12:19 am
Subject: Re: [SWMM-USERS] PSD and TSS
To: SWMM-...@LISTSERV.UOGUELPH.CA


> Hi Rishon,
>
> Does this mean that different buildup/washoff values need to be used
> for each TSS size group? Yes, you will have to have a different
> washoff value (Event mean concentration or EMC) value for each
> particle size but you can do without the buildup values if you just
> interested in the particle size removal in the wet pond. Each
> particle size range is considered a pollutant.
>
> A treatment expression for each particle size as a function of
> hydraulic residence time or depth might help you in your modeling. I
> am sure that you will get a lot of suggestions for removal equations
> from this posting.
>
> Robert Dickinson
> Innovyze Inc.
> 9340 Pontiac Drive                Tel:     813-712-0664 Tampa, Florida
> USA 33626 robert.d...@innovyze.com www.innovyze.com
>
>
> -----Original Message-----
> From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
> Rishon Richard
> Sent: Tuesday, May 29, 2012 12:00 AM
> To: SWMM-...@LISTSERV.UOGUELPH.CA
> Subject: [SWMM-USERS] PSD and TSS
>
> Hello,
>
> Given the Particle Size Distribution for TSS in a subcatchment, what
> is the most efficient method of modelling the removal/treatment of TSS
> in a pond in SWMM 5?
>
> Other threads have mentioned that the TSS PSD can be broken down by
> settling velocity characteristics. Does this mean that different
> buildup/washoff values need to be used for each TSS size group? Also,
> can someone please suggest a suitable treatment equation for TSS in a
> wet pond? I'm not sure if this thread was resolved:
> http://www.chiwater.com/BBS/forums/thread-view.asp?tid=2796&start=1
>
> Thank you,
>
> Rishon Richard
> Graduate Student in Enviro. Applied Science and Management Ryerson
> University, Toronto
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
> * In the body of the message type: signoff swmm-users *
> **********************************************************
>
> **********************************************************
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> * In the body of the message type: signoff swmm-users *
> **********************************************************

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

Date: Tue, 29 May 2012 10:42:19 -0400
From: Bill Lucas <wlu...@INTEGRATEDLAND.COM>
Subject: Re: PSD and TSS

Mike,

Thanks for the great exposition on pond algorithms. I learn a lot from this
thread.

I have a question though, even at the risk of revealing my total newbishness
to pollutant algorithms. As many of you know, I developed a method to route
flows through bioretention systems using Darcy Flow (which still doesn’t
exist in the LID modules). While the unsaturated responses are perhaps less
"correct" than what more complex algorithms will provide, they work well for
saturated flow which is where the routing rubber hits the road. I do this
in both CS (SWMM) and DS (HydroCAD) models (and try to stay away from BS!).

As part of this computation, I am developing several simple power functions
for N transformations based on retention time. HydroCAD computes plug flow
retention time explicitly, so easy to run the equation. OTOH, I am told
that SWMM does not compute plug flow retention time. However, it seems that
this factor must be computed internally in order to run Stoke's Law. If so,
is there a simple way to obtain this data?

Thanks in advance for your suggestions/comments.

Regards,

Bill Lucas.


-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
Gregory, Mike (Canada)
Sent: Tuesday, May 29, 2012 9:52 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

I've been setting up my TSS models for pond design using Bob's suggestion
(i.e., each TSS size fraction is represented as a separate pollutant).
Treatment expressions are based on depth according to NURP size fractions &
settling velocities (pg 33 of EPA-440-5-87-001). For example with the
smallest 20% fraction (0.03 ft/hr average settling velocity according to
NURP, and note that SWMM needs ft/s)...
If residual of say 25 mg/l, then: C = 25 + (TSS_1-25) *
EXP(-0.00000833/DEPTH*DT)
If no residual then simply: C = TSS_1 * EXP(-0.00000833/DEPTH*DT)

I'm not smart enough to know the difference between exponential & other
functions with SWMM water quality, but for TSS I just use the power function
normalized by area with max buildup rates and washoff EMCs that vary by
surface cover type (higher TSS for the urban/agriculture land uses, and
lower TSS for the vegetated/natural areas). The power rate constant is a
very sensitive parameter for TSS loading and I generally adjust this for
each project so that I end up with unit loading rates from 500 kg/ha/yr (450
lb/ac/yr) to 2000 kg/ha/yr (1800 lb/ac/yr), depending on land
use/imperviousness upstream of the pond, using an average year continuous
simulation. I'd be ashamed to call this "calibration" - real monitoring
results would be greatly welcomed (using sampling that distinguishes the
surface washload PSD from the pond outlet PSD - these differ by an order of
magnitude!).

Average annual TSS removal efficiency results for recent pond designs using
this methodology (7 big urban ponds) range from 62% to 87% for the smallest
0-20% fraction (equiv 3 micron diameter particles and less), and from 95% to
100% for the middlest 40-60% fraction (7-17um). The biggest 80-100%
fraction (>35um) almost always settles out in the pond quite quickly.
Overall removal (all size fractions combined) has been 88% to 97% which
exceeds our local presumptive design criteria for TSS in wet ponds. Of
course, this diminishes greatly as the pond ages and loads up on settled
particles. Reminder to use the dry bulk densities for each size fraction
(accounting for organics/metals as necessary) when using model results to
estimate accumulated pond sediment volumes for future dredge scheduling.


Regards,
mike g.

Michael A. Gregory, P.Eng., P.E.
AECOM - Kitchener, Canada

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
Rishon Richard
Sent: Tuesday, May 29, 2012 1:56 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Thank you for the quick reply. Does this also apply to the exponential
buildup/washoff functions? And if different values are required, where might
I be able to find them or how might I go about calculating them?

----- Original Message -----
From: Robert Dickinson <Robert.E....@INNOVYZE.COM>
Date: Tuesday, May 29, 2012 12:19 am
Subject: Re: [SWMM-USERS] PSD and TSS
To: SWMM-...@LISTSERV.UOGUELPH.CA


> Hi Rishon,
>
> Does this mean that different buildup/washoff values need to be used
> for each TSS size group? Yes, you will have to have a different
> washoff value (Event mean concentration or EMC) value for each
> particle size but you can do without the buildup values if you just
> interested in the particle size removal in the wet pond. Each
> particle size range is considered a pollutant.
>
> A treatment expression for each particle size as a function of
> hydraulic residence time or depth might help you in your modeling. I
> am sure that you will get a lot of suggestions for removal equations
> from this posting.
>
> Robert Dickinson
> Innovyze Inc.
> 9340 Pontiac Drive                Tel:     813-712-0664 Tampa, Florida
> USA 33626 robert.d...@innovyze.com www.innovyze.com
>
>
> -----Original Message-----
> From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
> Rishon Richard
> Sent: Tuesday, May 29, 2012 12:00 AM
> To: SWMM-...@LISTSERV.UOGUELPH.CA
> Subject: [SWMM-USERS] PSD and TSS
>
> Hello,
>
> Given the Particle Size Distribution for TSS in a subcatchment, what
> is the most efficient method of modelling the removal/treatment of TSS
> in a pond in SWMM 5?
>
> Other threads have mentioned that the TSS PSD can be broken down by
> settling velocity characteristics. Does this mean that different
> buildup/washoff values need to be used for each TSS size group? Also,
> can someone please suggest a suitable treatment equation for TSS in a
> wet pond? I'm not sure if this thread was resolved:
> http://www.chiwater.com/BBS/forums/thread-view.asp?tid=2796&start=1
>
> Thank you,
>
> Rishon Richard
> Graduate Student in Enviro. Applied Science and Management Ryerson
> University, Toronto
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
> * In the body of the message type: signoff swmm-users *
> **********************************************************
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
> * In the body of the message type: signoff swmm-users *
> **********************************************************

**********************************************************
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**********************************************************

**********************************************************
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**********************************************************

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

Date: Tue, 29 May 2012 15:01:43 +0000
From: "Gregory, Mike (Canada)" <Mike.G...@AECOM.COM>
Subject: Re: PSD and TSS

You might need to go back to SWMM4 for that, Bill. SWMM4 had two options for particulate settling: settling velocities like discussion below, and Stoke's combined with PSD input directly - see plug flow discussion in SWMM4 manual Appendix IV - Storage/Treatment Simulation).

Regards,
mike g.

Michael A. Gregory, P.Eng., P.E.
AECOM - Kitchener, Canada

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Bill Lucas
Sent: Tuesday, May 29, 2012 10:42 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Mike,

Thanks for the great exposition on pond algorithms. I learn a lot from this thread.

I have a question though, even at the risk of revealing my total newbishness to pollutant algorithms. As many of you know, I developed a method to route flows through bioretention systems using Darcy Flow (which still doesn't exist in the LID modules). While the unsaturated responses are perhaps less "correct" than what more complex algorithms will provide, they work well for saturated flow which is where the routing rubber hits the road. I do this in both CS (SWMM) and DS (HydroCAD) models (and try to stay away from BS!).

As part of this computation, I am developing several simple power functions for N transformations based on retention time. HydroCAD computes plug flow retention time explicitly, so easy to run the equation. OTOH, I am told that SWMM does not compute plug flow retention time. However, it seems that this factor must be computed internally in order to run Stoke's Law. If so, is there a simple way to obtain this data?

Thanks in advance for your suggestions/comments.

Regards,

Bill Lucas.


-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Gregory, Mike (Canada)
Sent: Tuesday, May 29, 2012 9:52 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

I've been setting up my TSS models for pond design using Bob's suggestion (i.e., each TSS size fraction is represented as a separate pollutant).
Treatment expressions are based on depth according to NURP size fractions & settling velocities (pg 33 of EPA-440-5-87-001). For example with the smallest 20% fraction (0.03 ft/hr average settling velocity according to NURP, and note that SWMM needs ft/s)...
If residual of say 25 mg/l, then: C = 25 + (TSS_1-25) *
EXP(-0.00000833/DEPTH*DT)
If no residual then simply: C = TSS_1 * EXP(-0.00000833/DEPTH*DT)

I'm not smart enough to know the difference between exponential & other functions with SWMM water quality, but for TSS I just use the power function normalized by area with max buildup rates and washoff EMCs that vary by surface cover type (higher TSS for the urban/agriculture land uses, and lower TSS for the vegetated/natural areas). The power rate constant is a very sensitive parameter for TSS loading and I generally adjust this for each project so that I end up with unit loading rates from 500 kg/ha/yr (450
lb/ac/yr) to 2000 kg/ha/yr (1800 lb/ac/yr), depending on land use/imperviousness upstream of the pond, using an average year continuous simulation. I'd be ashamed to call this "calibration" - real monitoring results would be greatly welcomed (using sampling that distinguishes the surface washload PSD from the pond outlet PSD - these differ by an order of magnitude!).

Average annual TSS removal efficiency results for recent pond designs using this methodology (7 big urban ponds) range from 62% to 87% for the smallest 0-20% fraction (equiv 3 micron diameter particles and less), and from 95% to 100% for the middlest 40-60% fraction (7-17um). The biggest 80-100% fraction (>35um) almost always settles out in the pond quite quickly.
Overall removal (all size fractions combined) has been 88% to 97% which exceeds our local presumptive design criteria for TSS in wet ponds. Of course, this diminishes greatly as the pond ages and loads up on settled particles. Reminder to use the dry bulk densities for each size fraction (accounting for organics/metals as necessary) when using model results to estimate accumulated pond sediment volumes for future dredge scheduling.


Regards,
mike g.

Michael A. Gregory, P.Eng., P.E.
AECOM - Kitchener, Canada

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Rishon Richard
Sent: Tuesday, May 29, 2012 1:56 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Thank you for the quick reply. Does this also apply to the exponential buildup/washoff functions? And if different values are required, where might I be able to find them or how might I go about calculating them?

----- Original Message -----
From: Robert Dickinson <Robert.E....@INNOVYZE.COM>
Date: Tuesday, May 29, 2012 12:19 am
Subject: Re: [SWMM-USERS] PSD and TSS
To: SWMM-...@LISTSERV.UOGUELPH.CA


> Hi Rishon,
>
> Does this mean that different buildup/washoff values need to be used
> for each TSS size group? Yes, you will have to have a different
> washoff value (Event mean concentration or EMC) value for each
> particle size but you can do without the buildup values if you just
> interested in the particle size removal in the wet pond. Each
> particle size range is considered a pollutant.
>
> A treatment expression for each particle size as a function of
> hydraulic residence time or depth might help you in your modeling. I
> am sure that you will get a lot of suggestions for removal equations
> from this posting.
>
> Robert Dickinson
> Innovyze Inc.
> 9340 Pontiac Drive                Tel:     813-712-0664 Tampa, Florida
> USA 33626 robert.d...@innovyze.com www.innovyze.com
>
>
> -----Original Message-----
> From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
> Rishon Richard
> Sent: Tuesday, May 29, 2012 12:00 AM
> To: SWMM-...@LISTSERV.UOGUELPH.CA
> Subject: [SWMM-USERS] PSD and TSS
>
> Hello,
>
> Given the Particle Size Distribution for TSS in a subcatchment, what
> is the most efficient method of modelling the removal/treatment of TSS
> in a pond in SWMM 5?
>
> Other threads have mentioned that the TSS PSD can be broken down by
> settling velocity characteristics. Does this mean that different
> buildup/washoff values need to be used for each TSS size group? Also,
> can someone please suggest a suitable treatment equation for TSS in a
> wet pond? I'm not sure if this thread was resolved:
> http://www.chiwater.com/BBS/forums/thread-view.asp?tid=2796&start=1
>
> Thank you,
>
> Rishon Richard
> Graduate Student in Enviro. Applied Science and Management Ryerson
> University, Toronto
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
> * In the body of the message type: signoff swmm-users *
> **********************************************************
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
> * In the body of the message type: signoff swmm-users *
> **********************************************************

**********************************************************
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------------------------------

Date: Tue, 29 May 2012 11:58:24 -0400
From: Bill Lucas <wlu...@INTEGRATEDLAND.COM>
Subject: Re: PSD and TSS

Thanks again Mike,

I see that computations can be computed as f(HRT), so that should be where I
begin in SWMM5. That brings me to the next question. How is HRT computed in
SWMM5? Several different ways to skin that cat and I cannot find any
documentation on which method is used.

The SWMM5 Manual briefly discusses the SWMM4 Storage/Treatment Module
including plug flow on pp. 716-717. However, the retained stressors are
then removed by "residual flow" which is not what is really happening when N
is transformed. I remain perplexed.

It seems that I could use your exponential equation, fiddle with the
coefficients, plug in a "depth", and get a similar response that wouldn’t
have this issue. I gather DT is same as HRT.

Thanks again for all your help,

Bill L.

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
Gregory, Mike (Canada)
Sent: Tuesday, May 29, 2012 11:02 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

You might need to go back to SWMM4 for that, Bill. SWMM4 had two options
for particulate settling: settling velocities like discussion below, and
Stoke's combined with PSD input directly - see plug flow discussion in SWMM4
manual Appendix IV - Storage/Treatment Simulation).

Regards,
mike g.

Michael A. Gregory, P.Eng., P.E.
AECOM - Kitchener, Canada

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Bill
Lucas
Sent: Tuesday, May 29, 2012 10:42 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Mike,

Thanks for the great exposition on pond algorithms. I learn a lot from this
thread.

I have a question though, even at the risk of revealing my total newbishness
to pollutant algorithms. As many of you know, I developed a method to route
flows through bioretention systems using Darcy Flow (which still doesn't
exist in the LID modules). While the unsaturated responses are perhaps less
"correct" than what more complex algorithms will provide, they work well for
saturated flow which is where the routing rubber hits the road. I do this
in both CS (SWMM) and DS (HydroCAD) models (and try to stay away from BS!).

As part of this computation, I am developing several simple power functions
for N transformations based on retention time. HydroCAD computes plug flow
retention time explicitly, so easy to run the equation. OTOH, I am told
that SWMM does not compute plug flow retention time. However, it seems that
this factor must be computed internally in order to run Stoke's Law. If so,
is there a simple way to obtain this data?

Thanks in advance for your suggestions/comments.

Regards,

Bill Lucas.


-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
Gregory, Mike (Canada)
Sent: Tuesday, May 29, 2012 9:52 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

I've been setting up my TSS models for pond design using Bob's suggestion
(i.e., each TSS size fraction is represented as a separate pollutant).
Treatment expressions are based on depth according to NURP size fractions &
settling velocities (pg 33 of EPA-440-5-87-001). For example with the
smallest 20% fraction (0.03 ft/hr average settling velocity according to
NURP, and note that SWMM needs ft/s)...
If residual of say 25 mg/l, then: C = 25 + (TSS_1-25) *
EXP(-0.00000833/DEPTH*DT)
If no residual then simply: C = TSS_1 * EXP(-0.00000833/DEPTH*DT)

I'm not smart enough to know the difference between exponential & other
functions with SWMM water quality, but for TSS I just use the power function
normalized by area with max buildup rates and washoff EMCs that vary by
surface cover type (higher TSS for the urban/agriculture land uses, and
lower TSS for the vegetated/natural areas). The power rate constant is a
very sensitive parameter for TSS loading and I generally adjust this for
each project so that I end up with unit loading rates from 500 kg/ha/yr (450
lb/ac/yr) to 2000 kg/ha/yr (1800 lb/ac/yr), depending on land
use/imperviousness upstream of the pond, using an average year continuous
simulation. I'd be ashamed to call this "calibration" - real monitoring
results would be greatly welcomed (using sampling that distinguishes the
surface washload PSD from the pond outlet PSD - these differ by an order of
magnitude!).

Average annual TSS removal efficiency results for recent pond designs using
this methodology (7 big urban ponds) range from 62% to 87% for the smallest
0-20% fraction (equiv 3 micron diameter particles and less), and from 95% to
100% for the middlest 40-60% fraction (7-17um). The biggest 80-100%
fraction (>35um) almost always settles out in the pond quite quickly.
Overall removal (all size fractions combined) has been 88% to 97% which
exceeds our local presumptive design criteria for TSS in wet ponds. Of
course, this diminishes greatly as the pond ages and loads up on settled
particles. Reminder to use the dry bulk densities for each size fraction
(accounting for organics/metals as necessary) when using model results to
estimate accumulated pond sediment volumes for future dredge scheduling.


Regards,
mike g.

Michael A. Gregory, P.Eng., P.E.
AECOM - Kitchener, Canada

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
Rishon Richard
Sent: Tuesday, May 29, 2012 1:56 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Thank you for the quick reply. Does this also apply to the exponential
buildup/washoff functions? And if different values are required, where might
I be able to find them or how might I go about calculating them?

----- Original Message -----
From: Robert Dickinson <Robert.E....@INNOVYZE.COM>
Date: Tuesday, May 29, 2012 12:19 am
Subject: Re: [SWMM-USERS] PSD and TSS
To: SWMM-...@LISTSERV.UOGUELPH.CA


> Hi Rishon,
>
> Does this mean that different buildup/washoff values need to be used
> for each TSS size group? Yes, you will have to have a different
> washoff value (Event mean concentration or EMC) value for each
> particle size but you can do without the buildup values if you just
> interested in the particle size removal in the wet pond. Each
> particle size range is considered a pollutant.
>
> A treatment expression for each particle size as a function of
> hydraulic residence time or depth might help you in your modeling. I
> am sure that you will get a lot of suggestions for removal equations
> from this posting.
>
> Robert Dickinson
> Innovyze Inc.
> 9340 Pontiac Drive                Tel:     813-712-0664 Tampa, Florida
> USA 33626 robert.d...@innovyze.com www.innovyze.com
>
>
> -----Original Message-----
> From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
> Rishon Richard
> Sent: Tuesday, May 29, 2012 12:00 AM
> To: SWMM-...@LISTSERV.UOGUELPH.CA
> Subject: [SWMM-USERS] PSD and TSS
>
> Hello,
>
> Given the Particle Size Distribution for TSS in a subcatchment, what
> is the most efficient method of modelling the removal/treatment of TSS
> in a pond in SWMM 5?
>
> Other threads have mentioned that the TSS PSD can be broken down by
> settling velocity characteristics. Does this mean that different
> buildup/washoff values need to be used for each TSS size group? Also,
> can someone please suggest a suitable treatment equation for TSS in a
> wet pond? I'm not sure if this thread was resolved:
> http://www.chiwater.com/BBS/forums/thread-view.asp?tid=2796&start=1
>
> Thank you,
>
> Rishon Richard
> Graduate Student in Enviro. Applied Science and Management Ryerson
> University, Toronto
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
> * In the body of the message type: signoff swmm-users *
> **********************************************************
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
> * In the body of the message type: signoff swmm-users *
> **********************************************************

**********************************************************
* To sign off, email to: list...@listserv.uoguelph.ca *
* In the body of the message type: signoff swmm-users *
**********************************************************

**********************************************************
* To sign off, email to: list...@listserv.uoguelph.ca *
* In the body of the message type: signoff swmm-users *
**********************************************************

**********************************************************
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* In the body of the message type: signoff swmm-users *
**********************************************************

**********************************************************
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**********************************************************

**********************************************************
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**********************************************************

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

Date: Tue, 29 May 2012 10:05:33 -0600
From: Robert Dickinson <Robert.E....@INNOVYZE.COM>
Subject: Re: PSD and TSS

Hi Bill,

Thanks for the insightful questions from you and Mike Gregory - it is always good to harken back to SWMM 3 or SWMM 4 related questions for OTS.

Regarding HRT

The new hydraulic residence time equals the old hydraulic residence time plus the current time step times the increase in volume over the time step. There is a check to make sure that the residence time is zero when the storage is empty. The Inflow can also be negative so the HRT can decrease over time as well as increase.
HRT or the residence time is New Hydraulic Residence Time = (Old Hydraulic Residence Time + Time Step) * Volume / (Volume + Inflow * Time Step)

Robert Dickinson
Product Sector Leader for InfoSWMM
Innovyze Inc.
9340 Pontiac Drive                Tel:     813-712-0664
Tampa, Florida USA 33626       
robert.d...@innovyze.com
www.innovyze.com

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Bill Lucas
Sent: Tuesday, May 29, 2012 11:58 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Thanks again Mike,

I see that computations can be computed as f(HRT), so that should be where I begin in SWMM5. That brings me to the next question. How is HRT computed in SWMM5? Several different ways to skin that cat and I cannot find any documentation on which method is used.

The SWMM5 Manual briefly discusses the SWMM4 Storage/Treatment Module including plug flow on pp. 716-717. However, the retained stressors are then removed by "residual flow" which is not what is really happening when N is transformed. I remain perplexed.


It seems that I could use your exponential equation, fiddle with the coefficients, plug in a "depth", and get a similar response that wouldn't have this issue. I gather DT is same as HRT.

Thanks again for all your help,

Bill L.

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Gregory, Mike (Canada)
Sent: Tuesday, May 29, 2012 11:02 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

You might need to go back to SWMM4 for that, Bill. SWMM4 had two options for particulate settling: settling velocities like discussion below, and Stoke's combined with PSD input directly - see plug flow discussion in SWMM4 manual Appendix IV - Storage/Treatment Simulation).

Regards,
mike g.

Michael A. Gregory, P.Eng., P.E.
AECOM - Kitchener, Canada

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Bill Lucas
Sent: Tuesday, May 29, 2012 10:42 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Mike,

Thanks for the great exposition on pond algorithms. I learn a lot from this thread.

I have a question though, even at the risk of revealing my total newbishness to pollutant algorithms. As many of you know, I developed a method to route flows through bioretention systems using Darcy Flow (which still doesn't exist in the LID modules). While the unsaturated responses are perhaps less "correct" than what more complex algorithms will provide, they work well for saturated flow which is where the routing rubber hits the road. I do this in both CS (SWMM) and DS (HydroCAD) models (and try to stay away from BS!).

As part of this computation, I am developing several simple power functions for N transformations based on retention time. HydroCAD computes plug flow retention time explicitly, so easy to run the equation. OTOH, I am told that SWMM does not compute plug flow retention time. However, it seems that this factor must be computed internally in order to run Stoke's Law. If so, is there a simple way to obtain this data?

Thanks in advance for your suggestions/comments.

Regards,

Bill Lucas.


-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Gregory, Mike (Canada)
Sent: Tuesday, May 29, 2012 9:52 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

I've been setting up my TSS models for pond design using Bob's suggestion (i.e., each TSS size fraction is represented as a separate pollutant).
Treatment expressions are based on depth according to NURP size fractions & settling velocities (pg 33 of EPA-440-5-87-001). For example with the smallest 20% fraction (0.03 ft/hr average settling velocity according to NURP, and note that SWMM needs ft/s)...
If residual of say 25 mg/l, then: C = 25 + (TSS_1-25) *
EXP(-0.00000833/DEPTH*DT)
If no residual then simply: C = TSS_1 * EXP(-0.00000833/DEPTH*DT)

I'm not smart enough to know the difference between exponential & other functions with SWMM water quality, but for TSS I just use the power function normalized by area with max buildup rates and washoff EMCs that vary by surface cover type (higher TSS for the urban/agriculture land uses, and lower TSS for the vegetated/natural areas). The power rate constant is a very sensitive parameter for TSS loading and I generally adjust this for each project so that I end up with unit loading rates from 500 kg/ha/yr (450
lb/ac/yr) to 2000 kg/ha/yr (1800 lb/ac/yr), depending on land use/imperviousness upstream of the pond, using an average year continuous simulation. I'd be ashamed to call this "calibration" - real monitoring results would be greatly welcomed (using sampling that distinguishes the surface washload PSD from the pond outlet PSD - these differ by an order of magnitude!).

Average annual TSS removal efficiency results for recent pond designs using this methodology (7 big urban ponds) range from 62% to 87% for the smallest 0-20% fraction (equiv 3 micron diameter particles and less), and from 95% to 100% for the middlest 40-60% fraction (7-17um). The biggest 80-100% fraction (>35um) almost always settles out in the pond quite quickly.
Overall removal (all size fractions combined) has been 88% to 97% which exceeds our local presumptive design criteria for TSS in wet ponds. Of course, this diminishes greatly as the pond ages and loads up on settled particles. Reminder to use the dry bulk densities for each size fraction (accounting for organics/metals as necessary) when using model results to estimate accumulated pond sediment volumes for future dredge scheduling.


Regards,
mike g.

Michael A. Gregory, P.Eng., P.E.
AECOM - Kitchener, Canada

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Rishon Richard
Sent: Tuesday, May 29, 2012 1:56 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Thank you for the quick reply. Does this also apply to the exponential buildup/washoff functions? And if different values are required, where might I be able to find them or how might I go about calculating them?

----- Original Message -----
From: Robert Dickinson <Robert.E....@INNOVYZE.COM>
Date: Tuesday, May 29, 2012 12:19 am
Subject: Re: [SWMM-USERS] PSD and TSS
To: SWMM-...@LISTSERV.UOGUELPH.CA


> Hi Rishon,
>
> Does this mean that different buildup/washoff values need to be used
> for each TSS size group? Yes, you will have to have a different
> washoff value (Event mean concentration or EMC) value for each
> particle size but you can do without the buildup values if you just
> interested in the particle size removal in the wet pond. Each
> particle size range is considered a pollutant.
>
> A treatment expression for each particle size as a function of
> hydraulic residence time or depth might help you in your modeling. I
> am sure that you will get a lot of suggestions for removal equations
> from this posting.
>
> Robert Dickinson
> Innovyze Inc.
> 9340 Pontiac Drive                Tel:     813-712-0664 Tampa, Florida
> USA 33626 robert.d...@innovyze.com www.innovyze.com
>
>
> -----Original Message-----
> From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
> Rishon Richard
> Sent: Tuesday, May 29, 2012 12:00 AM
> To: SWMM-...@LISTSERV.UOGUELPH.CA
> Subject: [SWMM-USERS] PSD and TSS
>
> Hello,
>
> Given the Particle Size Distribution for TSS in a subcatchment, what
> is the most efficient method of modelling the removal/treatment of TSS
> in a pond in SWMM 5?
>
> Other threads have mentioned that the TSS PSD can be broken down by
> settling velocity characteristics. Does this mean that different
> buildup/washoff values need to be used for each TSS size group? Also,
> can someone please suggest a suitable treatment equation for TSS in a
> wet pond? I'm not sure if this thread was resolved:
> http://www.chiwater.com/BBS/forums/thread-view.asp?tid=2796&start=1
>
> Thank you,
>
> Rishon Richard
> Graduate Student in Enviro. Applied Science and Management Ryerson
> University, Toronto
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
> * In the body of the message type: signoff swmm-users *
> **********************************************************
>
> **********************************************************
> * To sign off, email to: list...@listserv.uoguelph.ca *
> * In the body of the message type: signoff swmm-users *
> **********************************************************

**********************************************************
* To sign off, email to: list...@listserv.uoguelph.ca *
* In the body of the message type: signoff swmm-users *
**********************************************************

**********************************************************
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* In the body of the message type: signoff swmm-users *
**********************************************************

**********************************************************
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**********************************************************

**********************************************************
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**********************************************************

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**********************************************************

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

Date: Tue, 29 May 2012 16:06:18 +0000
From: "Gregory, Mike (Canada)" <Mike.G...@AECOM.COM>
Subject: Re: PSD and TSS

I agree - f(DEPTH) calculations in SWMM5 are best suited to TSS and associated particulate forms of pollutants.

Don't apply discussion below to dissolved constituents - f(HRT) calculations would be more appropriate.

Regards,
mike g.

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Bill Lucas
Sent: Tuesday, May 29, 2012 11:58 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Thanks again Mike,

I see that computations can be computed as f(HRT), so that should be where I begin in SWMM5. That brings me to the next question. How is HRT computed in SWMM5? Several different ways to skin that cat and I cannot find any documentation on which method is used.

The SWMM5 Manual briefly discusses the SWMM4 Storage/Treatment Module including plug flow on pp. 716-717. However, the retained stressors are then removed by "residual flow" which is not what is really happening when N is transformed. I remain perplexed.


It seems that I could use your exponential equation, fiddle with the coefficients, plug in a "depth", and get a similar response that wouldn't have this issue. I gather DT is same as HRT.

Thanks again for all your help,

Bill L.

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Gregory, Mike (Canada)
Sent: Tuesday, May 29, 2012 11:02 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

You might need to go back to SWMM4 for that, Bill. SWMM4 had two options for particulate settling: settling velocities like discussion below, and Stoke's combined with PSD input directly - see plug flow discussion in SWMM4 manual Appendix IV - Storage/Treatment Simulation).

Regards,
mike g.

Michael A. Gregory, P.Eng., P.E.
AECOM - Kitchener, Canada

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Bill Lucas
Sent: Tuesday, May 29, 2012 10:42 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Mike,

Thanks for the great exposition on pond algorithms. I learn a lot from this thread.

I have a question though, even at the risk of revealing my total newbishness to pollutant algorithms. As many of you know, I developed a method to route flows through bioretention systems using Darcy Flow (which still doesn't exist in the LID modules). While the unsaturated responses are perhaps less "correct" than what more complex algorithms will provide, they work well for saturated flow which is where the routing rubber hits the road. I do this in both CS (SWMM) and DS (HydroCAD) models (and try to stay away from BS!).

As part of this computation, I am developing several simple power functions for N transformations based on retention time. HydroCAD computes plug flow retention time explicitly, so easy to run the equation. OTOH, I am told that SWMM does not compute plug flow retention time. However, it seems that this factor must be computed internally in order to run Stoke's Law. If so, is there a simple way to obtain this data?

Thanks in advance for your suggestions/comments.

Regards,

Bill Lucas.


-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Gregory, Mike (Canada)
Sent: Tuesday, May 29, 2012 9:52 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

I've been setting up my TSS models for pond design using Bob's suggestion (i.e., each TSS size fraction is represented as a separate pollutant).
Treatment expressions are based on depth according to NURP size fractions & settling velocities (pg 33 of EPA-440-5-87-001). For example with the smallest 20% fraction (0.03 ft/hr average settling velocity according to NURP, and note that SWMM needs ft/s)...
If residual of say 25 mg/l, then: C = 25 + (TSS_1-25) *
EXP(-0.00000833/DEPTH*DT)
If no residual then simply: C = TSS_1 * EXP(-0.00000833/DEPTH*DT)

I'm not smart enough to know the difference between exponential & other functions with SWMM water quality, but for TSS I just use the power function normalized by area with max buildup rates and washoff EMCs that vary by surface cover type (higher TSS for the urban/agriculture land uses, and lower TSS for the vegetated/natural areas). The power rate constant is a very sensitive parameter for TSS loading and I generally adjust this for each project so that I end up with unit loading rates from 500 kg/ha/yr (450
lb/ac/yr) to 2000 kg/ha/yr (1800 lb/ac/yr), depending on land use/imperviousness upstream of the pond, using an average year continuous simulation. I'd be ashamed to call this "calibration" - real monitoring results would be greatly welcomed (using sampling that distinguishes the surface washload PSD from the pond outlet PSD - these differ by an order of magnitude!).

Average annual TSS removal efficiency results for recent pond designs using this methodology (7 big urban ponds) range from 62% to 87% for the smallest 0-20% fraction (equiv 3 micron diameter particles and less), and from 95% to 100% for the middlest 40-60% fraction (7-17um). The biggest 80-100% fraction (>35um) almost always settles out in the pond quite quickly.
Overall removal (all size fractions combined) has been 88% to 97% which exceeds our local presumptive design criteria for TSS in wet ponds. Of course, this diminishes greatly as the pond ages and loads up on settled particles. Reminder to use the dry bulk densities for each size fraction (accounting for organics/metals as necessary) when using model results to estimate accumulated pond sediment volumes for future dredge scheduling.


Regards,
mike g.

Michael A. Gregory, P.Eng., P.E.
AECOM - Kitchener, Canada

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Rishon Richard
Sent: Tuesday, May 29, 2012 1:56 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] PSD and TSS

Thank you for the quick reply. Does this also apply to the exponential buildup/washoff functions? And if different values are required, where might I be able to find them or how might I go about calculating them?

----- Original Message -----
From: Robert Dickinson <Robert.E....@INNOVYZE.COM>
Date: Tuesday, May 29, 2012 12:19 am
Subject: Re: [SWMM-USERS] PSD and TSS
To: SWMM-...@LISTSERV.UOGUELPH.CA


> Hi Rishon,
>
> Does this mean that different buildup/washoff values need to be used
> for each TSS size group? Yes, you will have to have a different
> washoff value (Event mean concentration or EMC) value for each
> particle size but you can do without the buildup values if you just
> interested in the particle size removal in the wet pond. Each
> particle size range is considered a pollutant.
>
> A treatment expression for each particle size as a function of
> hydraulic residence time or depth might help you in your modeling. I
> am sure that you will get a lot of suggestions for removal equations
> from this posting.
>
> Robert Dickinson
> Innovyze Inc.
> 9340 Pontiac Drive                Tel:     813-712-0664 Tampa, Florida
> USA 33626 robert.d...@innovyze.com www.innovyze.com
>
>
> -----Original Message-----
> From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of
> Rishon Richard
> Sent: Tuesday, May 29, 2012 12:00 AM
> To: SWMM-...@LISTSERV.UOGUELPH.CA
> Subject: [SWMM-USERS] PSD and TSS
>
> Hello,
>
> Given the Particle Size Distribution for TSS in a subcatchment, what
> is the most efficient method of modelling the removal/treatment of TSS
> in a pond in SWMM 5?
>
> Other threads have mentioned that the TSS PSD can be broken down by
> settling velocity characteristics. Does this mean that different
> buildup/washoff values need to be used for each TSS size group? Also,
> can someone please suggest a suitable treatment equation for TSS in a
> wet pond? I'm not sure if this thread was resolved:
> http://www.chiwater.com/BBS/forums/thread-view.asp?tid=2796&start=1
>
> Thank you,
>
> Rishon Richard
> Graduate Student in Enviro. Applied Science and Management Ryerson
> University, Toronto
>
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End of SWMM-USERS Digest - 17 May 2012 to 29 May 2012 (#2012-50)
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