In CADD file blue represents gutter with or without inlet box and red are pipes and inlet boxes.
The catchment element would connect to a catch-basin (inlet) or a manhole node. It would not connect to a gutter directly. The gutter element is responsible to carry the overflow from the catch-basin (inlet) downstream. You can look at the "Connectivity Rules" in StormCAD to find the hydraulically correct connections between elements.
As per the questions in the schematic provided, I will try to answer them serially;
1. If you assign the Area 1 to Inlet 2 then StormCAD's GVF-Rational Solver would calculate the spread for the downstream gutter. You have setup some "fake" catch-basin upstream along with a gutter upstream to Inlet 2. It is possible to calculate the spread at the gutter upstream of Inlet 2 by connecting the catchment Area 1 to the "fake" catch-basin. I am guessing your gutter starts from the "fake" catch-basin but your inlet doesn't. Normally the structure for any storm water network is the node-link-node setup which means any link (conduit, gutter etc.) must have an upstream and a downstream node.
For this you should know that the flow in a gutter will be determined by its upstream inlet.
2. For this query you should understand the drainage of the area. For the catchment Area 2 you should find out how that area is draining. By checking the topography you can find out where the majority of runoff is flowing. The catchment delineation tool in StormCAD is a great tool to determine the flow direction for an area using the "trace downstream" tool. You can find out more about it here.
You should first understand how the catchment is draining by looking at the topography of the region. Even if there are elements within the area (viz. gutters, catch-basins etc.) the topography or terrain will dictate how the runoff flows over the area.
Here is another article which can be helpful in this case;
Depth and spread calculations for grate inlet in sag
Hope this helps.
Bentley Technical Support
Now, I am confused because last time Jessi suggested me that spread is calculated at the upstream of the inlet before the portion of flow is captured.If so then whether I assign catchment area by creating fake catchbasin at the upstream or I directly assign the catchment area at the inlet it will calculate the spread at the upstream of that particular inlet because the catchment area I assign at the starting of gutter also route the flow at that same inlet.
But, here you are saying it is responsible for downstream spread calculation.And, yes it will also bypass the flow at downstream but for now I am just wondering if there is gutter and inlet with only one catchment area and if I assign that area to inlet first it will calculate spread before flow capture (as per Jessi) and only route through connected pipe and gutter right?
Please clear me on this topic.
Correct, for an on-grade inlet, the spread reported at the catchbasin represents the spread at the upstream side of the inlet, before some (or all) of the approach flow is captured by the inlet. The key is to look at the spread where it is highest, and that is what StormCAD reports.
Here are my answers to your questions in your photos:
I) If the "fake catchbasin" does not actually exist but rather the gutter simply abruptly starts, then you could start the network at "inlet 2". Meaning, do not include "fake catchbasin" or "gutter 1" in the model. The reason is because the spread and depth reported at "inlet 2" will show you the highest/worst case conditions in that gutter (gutter 1), since, as explained above, that spread and depth are measured from the end of "gutter 1" as it approaches "inlet 2".
However, in your illustration, you have a single "area 1" catchment draining to both "inlet 2" and "gutter 2". In reality, there will be a certain catchment area whose runoff approaches "inlet 2" (flows onto "gutter 1"), and a certain catchment area that approaches "inlet 3" (flows onto "gutter 2").
So, to answer your question of "If I assign Area 1 to inlet 2, how will I know spread of gutter 1?" - you would know the spread in "gutter 1" by looking at the spread in "inlet 2".
II) Re: "If I have only one area for gutter 2 & inlet-4, where I have to assign the catchment area?"
I am not quite sure I understand your question, and your illustration has two gutters marked as "gutter 2". The catchment area that drains onto a particular gutter should be assigned to the downstream inlet. For example on the left side of your drawing, the catchment area that drains onto "gutter 2 will approach inlet-3, so that catchment area should be assigned to inlet-3.
If you have a terrain model, you can use the catchment delineation feature available in the CONNECT Edition, to help delineate catchment areas associated with catchbasins. You can read and watch more about this here: Using Catchment Delineation
From your second illustration, regarding "How to assign flows to gutter 2 to solve for spread without creating fake inlet at start of gutter 2"
As mentioned above, flow is "assigned" to a gutter by directing the catchment outflow node field to the downstream inlet. That runoff will essentially enter that upstream gutter, approach the assigned inlet, and spread will be calculated based on that flow, and any bypass flow that also came down that particular gutter.
Re: "If assign area to inlet, how will he know spread of gutter 1"
Again, you will know the spread in the gutter by looking at the spread in the downstream catchbasin, because the spread at an inlet is measured at the gutter on the upstream side, where spread is highest.
So, to reduce spread and depth at an on-grade inlet, you would need to increase the capacity of the upstream inlet (so that less bypass flow approaches the inlet in question), or add more inlets along the gutter (so again, more upstream flow is captured, and/or the contributing area to the inlet in question is reduced because some of it enters an additional inlet.).
For inlets in-sag, since water pools up around the inlet, the depth and spread are measured from the inlet itself, and the capacity of that inlet will impact the depth and spread at that inlet. See:
Why is it that no matter how large the inlet on grade is the gutter spread always remains the same?
I would also recommend our Stormwater Conveyance Modeling and Design book, for more on stormwater modeling theory and practice.
Jesse DringoliTechnical Support Manager, OpenFlows ProductsBentley Communities Site AdministratorBentley Systems, Inc.
Answer Verified By: Sushma Choure