SWMM-USERS Digest - 26 Jun 2008 to 27 Jun 2008 (#2008-116)
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Topics of the day:
1. RTK questions
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Date: Fri, 27 Jun 2008 10:24:04 -0700
From: Noah Walker <nwa...@DUDEK.COM>
Subject: Re: RTK questions
Bob notes that in continuous simulation, the antecedent moisture
conditions are recalculated based on previous rainfall events, current
weather and soil recovery. Tom makes an interesting note that the Unit
Hydrograph basis of the RTK method allows "extrapolation" (within
reason).
One of the useful features of the SWMM model is its ability to determine
the maximum capacity of the collection system under flooded conditions
(unless surcharge is set to very high values to simulate locked
manholes). Flow that cannot be conveyed in the system is "lost".
A few years ago standard practice took several low intensity, low volume
storm events from a limited flow measurement period and extrapolated
those to the Design Storm event of much higher intensity and volume.
This method overstated potential inflow and infiltration volumes and
rates by not considering the hydraulic limit of the collection system.
This hydraulic limit may occur at intensities or volumes that are much
lower than the design event.
The question is, do we build pipes/pumps/storage and treatment capacity
to capture the entire event or do we limit the amount of inflow and
infiltration by repair and rehabilitation?
Noah Walker
-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@listserv.uoguelph.ca] On Behalf Of
Robert E Dickinson
Sent: Thursday, June 26, 2008 7:09 PM
To: SWMM-...@listserv.uoguelph.ca
Subject: Re: [SWMM-USERS] RTK questions
Hi Mauricio,
Good question:
1. When simulating various months, how does the program deal with the
initial abstraction (maximum depth)when going from one month to the
next. Does it initilize the abstraction capacity as specified in the
parameters for that month, or does it carry a water balance from month
to month?
This would be better answered with a plot of the initial abstraction
over
time in SWMM 5 but the program cleverly adjusts the amount of ia as a
function of time and by month. So the initial abstraction is recovered
over time and changes as the simulated month changes during the
simulation. In code speak this is done in rdii.c in the following lines:
// --- recover a portion of the IA already used
UHData[j].iaUsed -= dt / 86400. * UnitHyd[j].ia[m][IA_REC];
// --- determine amount of unused IA
m = datetime_monthOfYear(aDate) - 1;
ia = UnitHyd[j].ia[m][IA_MAX] - UHData[j].iaUsed;
ia = MAX(ia, 0.0);
Best and Kind Regards,
Robert Edgar Dickinson
MWH Soft Inc.
Tom Walski <Tom.W...@BENTLEY.COM>
Sent by: SWMM-USERS <SWMM-...@listserv.uoguelph.ca>
06/26/2008 09:42 PM
Please respond to
SWMM-USERS <SWMM-...@listserv.uoguelph.ca>
To
SWMM-...@listserv.uoguelph.ca
cc
Subject
Re: [SWMM-USERS] RTK questions
#1 is the primary shortcomings of the RTK method. R, T and K are
calibrated parameters and in particular R and T can vary with antecedent
moisture conditions. There were a couple of good talks at the WEF
Collection system conference this year that touched on this subject.
I would not be concerned with #2 so much, as part of the beauty of unit
hydrograph methods is that they can be extrapolated (within reason) to
storms of different duration, especially once you get past the impacts
of the antecedent moisture conditions.
Tom Walski
-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@listserv.uoguelph.ca] On Behalf Of
Mauricio Herrera
Sent: Thursday, June 26, 2008 7:28 PM
To: SWMM-...@listserv.uoguelph.ca
Subject: [SWMM-USERS] RTK questions
Hi,
I have a couple of questions regarding RTK in SWMM5:
1. When simulating various months, how does the program deal with the
initial abstraction (maximum depth)when going from one month to the
next. Does it initilize the abstraction capacity as specified in the
parameters for that month, or does it carry a water balance from month
to month?
2. When projecting flows using design storms, how to deal with storm
durations that are different to the ones used in the calibration. Should
I modify my RTK parameters? if so, how to do it?
Thank you, any guidance is greatly appreciated
Regards,
Mauricio Herrera
CH2M HILL
Metrotower II, Suite 2100
4720 Kingsway
Burnaby, BC V5H 4N2
Tel: 604.684.3282
Fax: 604.684.3292
Direct: 604.439.2354
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End of SWMM-USERS Digest - 26 Jun 2008 to 27 Jun 2008 (#2008-116)
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