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Modeling Gutters in SewerGEMS: Flow, Depth, and Spread

I am modeling a storm sewer system in SewerGEMS using the dynamic wave solver. After reading all the documentation on modeling gutters, I still have some questions:

1. What happens when the flow in a gutter exceeds it's maximum capacity, or the depth is greater than the maximum of the defined cross section. In my opinion, there should either be a warning or an error message when this occurs, since the resulting depth or spread values are no longer meaningful (unless there are infinitely high vertical walls at the beginning and end of the cross section).

2. What is the best way to model a gutter system where the curb and/or crown of the street is inundated at certain flood frequencies? SewerGEMS does not calculate depth or spread for irregular gutter types. Why is that? My workaround has been to take the maximum flow in the gutter and using that to calculate the depth with FlowMaster.

3. Why is inlet overflow lost to the simulation? Should it not be added as flow to the downstream gutter if it exists?

Any modeling strategies or similar issues you have would be appreciated!

Parents
  • Hi rdueck,

    Regarding questions #1 and #2, I'm checking into a few things first so I can give you a complete and accurate answer.

    For #3, if the subsurface piping overflows out of the catchbasin, that overflow is accounted for in the downstream gutter. Check the Help topic called "Flooding":

    • If there is a surface gutter or channel connected to the manhole, the overflowing water will join the surface gutter or channel and will be accounted for and simulated as part of the flows in the gutter subsystem. These flows may drain back to the sewer subsystem somewhere downstream.


    If there is no attached gutter, the overflow would be lost. For a sag location, you could use the "Surface Storage" option mentioned in this help topic. 

    Thanks for your patience,


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

    Answer Verified By: Randy Dueck 

Reply
  • Hi rdueck,

    Regarding questions #1 and #2, I'm checking into a few things first so I can give you a complete and accurate answer.

    For #3, if the subsurface piping overflows out of the catchbasin, that overflow is accounted for in the downstream gutter. Check the Help topic called "Flooding":

    • If there is a surface gutter or channel connected to the manhole, the overflowing water will join the surface gutter or channel and will be accounted for and simulated as part of the flows in the gutter subsystem. These flows may drain back to the sewer subsystem somewhere downstream.


    If there is no attached gutter, the overflow would be lost. For a sag location, you could use the "Surface Storage" option mentioned in this help topic. 

    Thanks for your patience,


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

    Answer Verified By: Randy Dueck 

Children
  • Hello rdueck,

    Apologies for the delay in response.

    Regarding question #1, the "Maximum Gutter Depth" field is used differently depending on the gutter configuration (such as whether you choose to have the gutter link use the shape of the upstream catchbasin node) and active numerical solver (such as Explicit SWMM or Implicit). In some cases, it is used to calculate the rating table of the Channel used to represent the gutter link element. See the chapter in the help called "Gutter System Hydraulics" for more on that.

    Currently we do not produce a warning when the gutter depth (at the link or node) exceeds the maximum depth, but an information message like that is a good suggestion (for all solvers), which I have logged to our developers on your behalf (reference number 97735).

    Regarding question #2, the Irregular shape is supported for the gutter link element, but not for the catcbasin (gutter at the inlet location). It is not part of the HEC-22 standard that we use for inlet calculations and there are some other technical reasons behind why this isn't supported. So, you should be able to set the shape to something else at the catchbasin and still keep it set to Irregular in the gutter link element itself. Then, look at the gutter link to check for depth/spread at the next downstream inlet.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

    Answer Verified By: Randy Dueck 

  • Hey Jesse

    As a follow up (sorta), how does stormcad calculate the street/gutter capacity when we have a parabolic street section with a 5" crown but a 6" curb? In other words, when the crown is an inch below the top of curb, is that extra inch of cross section capacity not accounted for? Or can it be? How can we do it? A second question relates to inlet capacity of same cross section. If we have a catalog inlet that is defined in the library with a 4" local depression24" depression width and 90 degree throat angle, we would not need to put a depressed gutter, gutter width, gutter cross slope in the catch basin flex table. In other words, we would not need to over ride the parabolic cross section (the actual type we have and used in the gutter flex table) with a conventional gutter shape in the catch basin flex table. We do not have a continuous depressed gutter in cross section, only a local depression at each inlet.