SWMM-USERS Digest - 20 Apr 2012 to 23 Apr 2012 (#2012-41)

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Apr 24, 2012, 12:00:10 AM4/24/12

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There are 2 messages totaling 358 lines in this issue.

Topics of the day:

1. Rain barrel routing questions (2)

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Date: Mon, 23 Apr 2012 09:14:55 +0000
From: "Myers, Dwayne" <Mye...@CDMSMITH.COM>
Subject: Re: Rain barrel routing questions

I might be stating the obvious, but with any kind of stormwater management, the drainage area that is being controlled (in this case, the roofs draining to rain barrels) has to be separated from the drainage area that is not (everything else). Otherwise you have uncontrolled drainage area going to storage, which is non-conservative (i.e. wrong).

Dwayne Myers
CDM Smith

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of William Frost
Sent: Saturday, April 21, 2012 1:27 AM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] Rain barrel routing questions

I would concur with the consultant's conclusion. Given a 50 gal rain barrel at each downspout and ~600 SF of roof per downspout, rain barrels will be full after the first ~0.15" of rain, after which they'll be bypassed. They just lop off the lead part of the hydrograph, not the peak. The rainfall that causes flooding will occur after the barrel is full.

For a SWMM model, I'd increase the depression storage coefficient to match what is expected to be captured by the rain barrels. First calculate the volume captured by the rainbarrels, then take that volume and apply it over the whole catchment impervious area to get the depth of depression storage.

Bill Frost, PE, D.WRE
KCI Technologies, Inc.
Sparks, MD

-----Original Message-----
From: SWMM-USERS [mailto:SWMM-...@LISTSERV.UOGUELPH.CA] On Behalf Of Roger Leventhal
Sent: Friday, April 20, 2012 12:50 PM
To: SWMM-...@LISTSERV.UOGUELPH.CA
Subject: Re: [SWMM-USERS] Rain barrel routing questions

I had a follow-on question to the modeling of rain barrels for flood
reduction benefits.

I am reviewing a report where the City requested an evaluation of the use
of rain barrels at homes in an urbanized watershed as a strategy to help
reduce downstream flooding. The consultants calculated the total potential
rainbarrel storage volume and then increased the initial abstraction
parameter in their model (they used HEC-HMS but I believe SWMM has an
equivalent parameter). They concluded that rain barrels would have a very
small effect on downstream flooding and therefore wasnt worth considering.

This approach seems reasonable to me but I was curious if anyone had looked
into this idea before and came to a similar conclusion or could suggest a
better way to model rain barrels or cisterns. I am sure the consultant
didn't have budget to add a storage tank at each house so they were looking
at reasonable but larger scale ways to assess the effectiveness of
micro-storage.

Any thoughts welcome, Roger

On Mon, Apr 16, 2012 at 10:25 AM, Shannon Reynolds <reyno...@gmail.com>wrote:

> Thanks for the responses!
>
> Shannon
>
> On Mon, Apr 16, 2012 at 5:59 AM, Lewis Rossman <
> Rossma...@epamail.epa.gov> wrote:
>
> > No. The flows in each stream at the current time step are combined.
> > There is no delay in the overflow from a full rain barrel.
> >
> >
> --------------------------------------------------------------------------------------
> >
> > Lewis Rossman
> > Environmental Scientist
> > Water Supply and Water Resources Division
> > U.S Environmental Protection Agency
> > email: rossma...@epa.gov
> >
> >
> >
> > From: Shannon Reynolds <reyno...@GMAIL.COM>
> > To: SWMM-...@LISTSERV.UOGUELPH.CA
> > Date: 04/13/2012 04:13 PM
> > Subject: Re: [SWMM-USERS] Rain barrel routing questions
> > Sent by: SWMM-USERS <SWMM-...@LISTSERV.UOGUELPH.CA>
> >
> >
> >
> > Thank you for the reply. One more quick question, when you say the drain
> > line flow and the overflow are combined together before routing to the
> > subcatchment outlet (or pervious area), does that mean the overflow
> > routing
> > to the outlet (or pervious area) is delayed according to the delay time
> > specified for the rain barrel?
> >
> > Cheers,
> > Shannon
> >
> > On Fri, Apr 13, 2012 at 11:32 AM, Lewis Rossman <
> > Rossma...@epamail.epa.gov> wrote:
> >
> > > Both the rain barrel overflow and the its drain line flow are combined
> > > together before routing to the subcatchment's outlet. If the "send to
> > > pervious"option is used then, again, the combined overflow and
> > > underdrain flow from the unit are sent to the subcatchment's pervious
> > > area (not to the outlet).
> > >
> > > Allowing the underdrain to have a different outlet destination is on
> > the
> > > "to do" list for a future update.
> > >
> > > Lewis Rossman
> > > Environmental Scientist
> > > Water Supply and Water Resources Division
> > > U.S Environmental Protection Agency
> > > email: rossma...@epa.gov
> > > **********************************************************
> > > * 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 *
> > **********************************************************
> >
> >
> >
> --------------------------------------------------------------------------------------
> >
> >
> > Lewis Rossman
> > Environmental Scientist
> > Water Supply and Water Resources Division
> > U.S Environmental Protection Agency
> > email: rossma...@epa.gov
> >
> > **********************************************************
> > * 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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>

Roger Leventhal, P.E.
11 Camelot Court
Kensington, CA 94707
415-473-3249 ph

><((((º>`·. .· `·. .· `·... ><((((º> .
· `·. . , . .· `·.. ><((((º>`·. .· `·. .· `·... ><((((º>

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

Date: Mon, 23 Apr 2012 09:06:48 -0400
From: "Kacvinsky, Greg" <Greg.Ka...@OHM-ADVISORS.COM>
Subject: Re: Rain barrel routing questions

I believe the main issue with interpreting results from rain barrels (or similar stormwater BMPs) is the difference between event-based and continuous modeling. For an event-based model (i.e. 10-year storm of short duration), the rain barrels will show little to no impact. When you run a continuous (i.e. 12-month) rainfall data series, you will see a significant impact on total runoff volume over the period of analysis (if the modeled BMPs intercept a significant component of the modeled runoff).

Many cities (and other regulatory agencies) still think in terms of the event-based analysis, and have not yet evolved to the idea of a continuous model. Until our stormwater rules change to place more weight on long-term stormwater volume calculations, stormwater BMP analysis will be misunderstood.

Regards,
Greg

Gregory P. Kacvinsky, PE

Project Manager

OHM | Architects. Engineers. Planners.
34000 Plymouth Road
Livonia, MI 48150
p. 734.522.6711
f. 734.522.6427
d. 734.466.4476
m. 217.979.0422

Advancing Communities

www.ohm-advisors.com

This message, including attachments, is confidential and may be privileged. If you are not an intended recipient, please notify the sender then delete and destroy the original message and all copies. You should not copy, forward and/or disclose this message, in whole or in part, without permission of the sender.

I had a follow-on question to the modeling of rain barrels for flood
reduction benefits.

Any thoughts welcome, Roger

On Mon, Apr 16, 2012 at 10:25 AM, Shannon Reynolds <reyno...@gmail.com>wrote:

Roger Leventhal, P.E.
11 Camelot Court
Kensington, CA 94707
415-473-3249 ph

><((((º>`·. .· `·. .· `·... ><((((º> .
· `·. . , . .· `·.. ><((((º>`·. .· `·. .· `·... ><((((º>

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End of SWMM-USERS Digest - 20 Apr 2012 to 23 Apr 2012 (#2012-41)
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