There are 5 messages totalling 420 lines in this issue.
1. PCSWMM: Status Report (5)
-----Original Message-----
From: SWMM-USERS [mailto:SWMM-US
...@listserv.uoguelph.ca] On Behalf Of
Stephanie Piers de Raveschoot
Sent: Thursday, May 15, 2008 11:17
To: SWMM-US
...@listserv.uoguelph.ca
Subject: [SWMM-USERS] PCSWMM: Status Report
Hello,
I am having some trouble fully understanding some of the elements
from
the Status Report.
- what exactly is a "continuity error" ?
- what exactly is this unit: "ha-mm" ?
- what is the "Highest flow Instability Indexes", and how is it
measured?
Additionally, some of the results I obtain do not appear to me as quite
obvious. Indeed, for the same contributing subcatchment, and for a same
raingage, I get different answers from my junctions: one has water
ponding,
and the other not. Of course, the dimension of the conduits is a
determining
factor, but however the difference between the two seems quite large. Is
there any parameter I could have forgotten to check ?
In advance thank you for any help !
Stephanie
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------------------------------
Date: Thu, 15 May 2008 10:55:55 -0500
From: Thomas M Over <tmo...@USGS.GOV>
Subject: Re: PCSWMM: Status Report
I was just going to say a hectare-mm is a lot less (actually I guess about
a tenth) than an acre-foot!
Sorry if small jokes are not allowed.
Tom
"Rosenberg, Dan" <Dan.Rosenb...@M-E.AECOM.COM>
Sent by: SWMM-USERS <SWMM-US...@listserv.uoguelph.ca>
05/15/2008 10:41 AM
Please respond to
SWMM-USERS <SWMM-US...@listserv.uoguelph.ca>
To
SWMM-US...@listserv.uoguelph.ca
cc
Subject
Re: [SWMM-USERS] PCSWMM: Status Report
Stephanie,
The continuity error is the difference it the total inflow, outflow and
volume remaining in the model network taking into account the dry pipe
flow generated by the model. When the model iterates to solve for the
flow it sometimes "loses" or "gains" volume. Optimally, the continuity
error would be zero. A small amount of error is acceptable.
"ha-mm" is hectare-millimeters, the volume in millimeters of rainfall
over the area in hectares of your catchment.
The flow instability is, I believe, measured by the Courant number and
is a measure of the celerity in the pipes. This is essentially a measure
of the wave speed in proportion to the smallest time step. If the time
steps are too large your courant number will be large and there will be
more instability in the model and perhaps more possibility of error in
the results. That is my understanding; there may be more knowledgeable
readers out there to answer this one.
As for the specifics of your model it would be difficult to hazard a
guess without the model information.
Daniel M. Rosenberg, P.E.
Metcalf & Eddy of Ohio, Inc.
1375 E. 9th Street, Suite 2801
Cleveland OH, 44114
(216) 910-1929
www.aecom.com
-----Original Message-----
From: SWMM-USERS [mailto:SWMM-US...@listserv.uoguelph.ca] On Behalf Of
Stephanie Piers de Raveschoot
Sent: Thursday, May 15, 2008 11:17
To: SWMM-US...@listserv.uoguelph.ca
Subject: [SWMM-USERS] PCSWMM: Status Report
Hello,
I am having some trouble fully understanding some of the elements
from
the Status Report.
- what exactly is a "continuity error" ?
- what exactly is this unit: "ha-mm" ?
- what is the "Highest flow Instability Indexes", and how is it
measured?
Additionally, some of the results I obtain do not appear to me as quite
obvious. Indeed, for the same contributing subcatchment, and for a same
raingage, I get different answers from my junctions: one has water
ponding,
and the other not. Of course, the dimension of the conduits is a
determining
factor, but however the difference between the two seems quite large. Is
there any parameter I could have forgotten to check ?
In advance thank you for any help !
Stephanie
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------------------------------
Date: Thu, 15 May 2008 12:01:03 -0400
From: Robert E Dickinson <Robert.E.Dickin...@US.MWHGLOBAL.COM>
Subject: Re: PCSWMM: Status Report
Hi Stephanie,
The "Highest flow Instability Index" is an attempt to quantify the
instability of the simulated flow in a link. It measures how many flow
"turns" of 0.001 cfs or more occur duing a simulation. [CFS are the
internal units in SWMM 5]. For example, if the link flows were these for
three consecutive hydraulic time steps the number of flow turns would be
1:
time n-1 99
time n 99.1
time n+1 99
In other words it is a measurement of the number of small, medium or large
oscillations in the link flow. The number actually printed out in the
output table of SWMM 5 is:
100.0 * LinkStats[j].flowTurns / (2./3.*(StepCount-2))
where, StepCount is the total number of hydraulic time steps during the
simulation.
The way I use this table is too visually look at the links with the
highest index and see if they LOOK unstable to me. You cannot tell just
from the absolute value of the index if the flow is really unstable. A
link with many tiny oscillations will have the same index as a link with
many large osciallations.
Best and Kind Regards,
Robert Edgar Dickinson
MWH Soft Inc.
Stephanie Piers de Raveschoot <stephanie.pi...@EPFL.CH>
Sent by: SWMM-USERS <SWMM-US...@listserv.uoguelph.ca>
05/15/2008 11:16 AM
Please respond to
SWMM-USERS <SWMM-US...@listserv.uoguelph.ca>
To
SWMM-US...@listserv.uoguelph.ca
cc
Subject
[SWMM-USERS] PCSWMM: Status Report
Hello,
I am having some trouble fully understanding some of the elements from
the Status Report.
- what exactly is a "continuity error" ?
- what exactly is this unit: "ha-mm" ?
- what is the "Highest flow Instability Indexes", and how is it measured?
Additionally, some of the results I obtain do not appear to me as quite
obvious. Indeed, for the same contributing subcatchment, and for a same
raingage, I get different answers from my junctions: one has water
ponding,
and the other not. Of course, the dimension of the conduits is a
determining
factor, but however the difference between the two seems quite large. Is
there any parameter I could have forgotten to check ?
In advance thank you for any help !
Stephanie
**********************************************************
* To sign off, email to: lists...@listserv.uoguelph.ca *
* In the body of the message type: signoff swmm-users *
**********************************************************
**********************************************************
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------------------------------
Date: Thu, 15 May 2008 09:10:10 -0700
From: Erika Schneider <eschnei...@INTERWESTGRP.COM>
Subject: Re: PCSWMM: Status Report
I've been told that anything less than 0.5% is considered acceptable
when it comes to continuity error. I'm curious... do most concur with
this percentage?
Erika Schneider, P.E.
Interwest Consulting Group
1218 W. Ash Street, Suite C
Windsor, CO 80550
TEL: 970-674-3300 Ext. 101
FAX: 970-674-3303
eschnei...@interwestgrp.com
-----Original Message-----
From: SWMM-USERS [mailto:SWMM-US...@listserv.uoguelph.ca] On Behalf Of
Rosenberg, Dan
Sent: Thursday, May 15, 2008 9:41 AM
To: SWMM-US...@listserv.uoguelph.ca
Subject: Re: [SWMM-USERS] PCSWMM: Status Report
Stephanie,
The continuity error is the difference it the total inflow, outflow and
volume remaining in the model network taking into account the dry pipe
flow generated by the model. When the model iterates to solve for the
flow it sometimes "loses" or "gains" volume. Optimally, the continuity
error would be zero. A small amount of error is acceptable.
"ha-mm" is hectare-millimeters, the volume in millimeters of rainfall
over the area in hectares of your catchment.
The flow instability is, I believe, measured by the Courant number and
is a measure of the celerity in the pipes. This is essentially a measure
of the wave speed in proportion to the smallest time step. If the time
steps are too large your courant number will be large and there will be
more instability in the model and perhaps more possibility of error in
the results. That is my understanding; there may be more knowledgeable
readers out there to answer this one.
As for the specifics of your model it would be difficult to hazard a
guess without the model information.
Daniel M. Rosenberg, P.E.
Metcalf & Eddy of Ohio, Inc.
1375 E. 9th Street, Suite 2801
Cleveland OH, 44114
(216) 910-1929
www.aecom.com
-----Original Message-----
From: SWMM-USERS [mailto:SWMM-US...@listserv.uoguelph.ca] On Behalf Of
Stephanie Piers de Raveschoot
Sent: Thursday, May 15, 2008 11:17
To: SWMM-US...@listserv.uoguelph.ca
Subject: [SWMM-USERS] PCSWMM: Status Report
Hello,
I am having some trouble fully understanding some of the elements
from
the Status Report.
- what exactly is a "continuity error" ?
- what exactly is this unit: "ha-mm" ?
- what is the "Highest flow Instability Indexes", and how is it
measured?
Additionally, some of the results I obtain do not appear to me as quite
obvious. Indeed, for the same contributing subcatchment, and for a same
raingage, I get different answers from my junctions: one has water
ponding,
and the other not. Of course, the dimension of the conduits is a
determining
factor, but however the difference between the two seems quite large. Is
there any parameter I could have forgotten to check ?
In advance thank you for any help !
Stephanie
**********************************************************
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**********************************************************
**********************************************************
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------------------------------
End of SWMM-USERS Digest - 14 May 2008 to 15 May 2008 (#2008-89)
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