Hi,
I have a model in which a pond goes to an outlet structure to go directly to our storm system. However, we want to discard the water quality volume from that same pond to go to arbitrary outfall so it does not affect downstream of our system. I know what the volume that I need to discard is.
Therefore, I was wondering if it would be as simple as having two outlet structures with pipe attached to each of them, one for the water quality volume and one for the rest of the flow? For the water quality volume the pipe after the outlet structure would end in an outfall.
How would I make sure that only the amount of XXX of volume is taken to that pipe?
Thanks
Paola,
In general you will want to model the system as close as possible to the real system. What in the real system limits the outflow based on volume? (how is that accomplished?)
You can indeed model multiple outlets leaving the same pond. See the "Pond" section of this article: Modeling a flow split (diversion) in SewerGEMS or CivilStorm
With the pond outlet structure component in SewerGEMS, you can control outflow based on the available outlet types: orifice, weir, riser, vortex valve, user defined rating table. If you want to assume a specific, constant outflow that yields a certain volume, you could use the user defined rating table pond outlet type, assign it to a second pond outlet node attached to the pond, then connect that to a free outfall via a conduit.
Or, if this specific volume you're looking to "discard" is actually infiltration (water soaking into the ground around the pond), you can use one of the available seepage methods.
Regards,
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.
Jesse, would probably looking through the question and answer that I found on this thread (in bold below) help me walk through how I take into account the seepage infiltration for that pond?
Seepage (infiltration) is a property of the pond element. You will see the attribute called "Pond Seepage Method" in the "Infiltration/Inflow & Seepage" section of the pond properties. You can choose between a few different methods depending on which numerical solver you are using.
Prior to today, more information could be found in the Help topic "pond flow loss". I have now documented information about seepage in our Wiki here: Available Pond Seepage (infiltration) and evaporation methods per solver
If none of these methods are suitable for your situation, you can indeed use the approach of modeling the infiltration/seepage with a user defined rating table (varying flow as a function of headwater elevation) on a separate pond outlet structure.
Okay i found the "Pond seepage method" in the section and it looks like we are using the explicit so my only option is either Green Ampt method or discarding in an infiltration outfall with user defined rating table. Are those the only two ways to account for infiltration flow not going into our system?
I am also looking into the water quality section and possibly doing a pollutant graph for the TSS. But right now i do not seem to have all the pollutants parameters.
I have tried to look online but still a little confused on what is the difference between explicit and implicit. And why do we use one over the other?
Paola Espinoza-Youn said:Are those the only two ways to account for infiltration flow not going into our system?
For a pond with the Explicit solver, yes. It should be fairly straightforward to set up the secondary pond outlet with user defined rating table, or adjust the Green-Ampt parameters until you get the desired infiltration rate.
Paola Espinoza-Youn said:I have tried to look online but still a little confused on what is the difference between explicit and implicit. And why do we use one over the other?
See: Differences between solvers: GVF-Convex vs. GVF-Rational vs. Implicit vs. Explicit (SWMM)
For a model with ponds where you need to route a hydrograph, the Explicit (SWMM) solver tends to be much more stable than the Implicit solver, and accounts for more dynamic effects compared to the more simplified GVF-Convex solver.
So the Gregg-Ampt Parameters are all soil properties, correct? That is what it seemed to be when I looked it up online. And then after I run the model, is that when I see what infiltration rate resulted from those soil Gregg-Ampt Parameters that I input.
Nevermind i see that I answered my own question regarding if they are soil properties. I did not see that it explains what the parameters are underneath when you click on it.
However, to get the desired infiltration rate. Is that something that I would see if I got the desired infiltration rate after I run the model or is that somewhere I can look someplace else before running it?
Thanks for helping!
Yes the Green-Ampt is the standard methodology which calculates the infiltration rate based on the Suction Head, Conductivity and Initial Deficit of the soil. If you click the name of the field you can see a description at the bottom of the Property Grid (plus they are documented in the Help). See: Where can I find the definition of a property?
I have added a few more details about these parameters to the new article, based on the EPA-SWMM manual.
Yes, if you graph the seepage result field, that will be the infiltration based on the parameters you set (flow lost to the system through soaking into the ground in the pond)