Spread Problem

Hello Hari,

In the system you have setup,

Fake Catch-basin > Gutter -1 > Next Catch-basin > Channel-27 >  Headwall > Pipe > Catch-basin

What elements in StormCAD did you use to model this setup?

Is it; CB-1 > GU-1 > CB-2 > CH-1 > H-1 > CO-1 > CB-3 ? or CB-1 > GU-1 > CB-2 > CH-1 > H-1 > CO-1 > O-1 ? 

Here, CB = Catch-basin Element, GU = Gutter Element, CH = Channel Element, H = Headwall Element, CO = Conduit Element, O = Outfall Element.

I tried modeling your case both ways. For the first it didn't analyze as there was no outfall present. For the second way, I was able to analyze. I am guessing that's the way you have setup, with outfall in the end.

As per your Case 1 you are getting "9.6 CFS bypassed flow in the gutter flex table". But there is only one gutter (GU-1) in the system and bypassed flow cannot be viewed in the "gutter". Bypassed flow is a property of the inlet (Catch-basin). I was able to see the bypassed flow in the Catch-basin. To simulate a case similar to yours in which you have 9.6 CFS as runoff from the catchment and 9.6 CFS as bypassed flow (i.e. no capture by Catch-basin), I kept the percent capture as 0.001 % (almost 0). Did you do a similar thing? By keeping this small value I did get a bypassed flow matching the runoff from my catchment.

Also, in your setup its natural that there won't be any flow in the Channel-27 since all of the flow from the catchment is bypassed. Since you don't have a gutter connecting from your Catch-basin to your headwall (which is also not possible because a gutter can connect to either a Catch-basin, cross-section or outfall) there is no way to carry the bypassed flow downstream. However, if you set the Catch-basin to "Full Capture" there will be flow in the Channel-27 equal to your catchment runoff. If you check the spread in the Catch-basin properties you will also find the spread calculated. The property to look for is "Spread / Top Width" in Catch-basin properties.

Even in the Gutter-1 properties if you search for the property "Spread / Top Width (Stop)" it will be the same spread calculated which concurs with what my colleague Jesse explained in an earlier response to your forum post. The spread is measured at the end of Gutter-1 as it enters the Catch-basin.

Also as suggested earlier by Jesse, the "fake" Catch-basin is hydraulically unnecessary in your setup as there is no flow entering into the system from that point.

Hope this helps.

The spread reported at a gutter represents the point where the spread is highest, which is the downstream catchbasin. Therefore if there is no downstream catchbasin, those results cannot be computed and they show as "N/A" in the gutter as you have observed. See: The spread/ top width (stop) in my gutter is N/A

Since the upstream catchbasin is "fake", it sounds like you have a gutter/ditch, that discharges into a channel. In that case, I would consider modeling "Gutter-1" as a channel and "fake catchbasin" as a cross section (configured with the irregular channel shape, to allow you to enter the gutter shape). This would enable you to see the spread by looking at the Flow-Width result field.

If you're using the Implicit numerical solver, channels are treated as non-prismatic. So, if the cross-sectional area of the "gutter" is constant, and there is an abrupt change to a different cross sectional shape in "channel-27", then you could model the "gutter-1" as a conduit instead, with the conduit type set to irregular to model the gutter shape.

However, in your screenshot of the model, I do not see any catchment connected to the "fake catchbasin". Wouldn't you have some flow entering along that gutter? (or is it entered in the Inflow Collection?).