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HGL & Surcharged Flow Rate for outfall pipe!

HGL & Surcharged Flow Rate for outfall pipe!

HGL & Surcharged Flow Rate for outfall pipe!

Hi there!
First of all thank you all for your valuable time and help. I'm almost new to this engineering field and I've learned a lot from this forum.
So, I'm sorry if my questions are long and silly!

We have a project in south Texas that is a 0.7 AC small land with a proposed hotel in it. I've attached our storm sewer design in photo #1. We asked to make pipes 6" from underground detention to the outfall, we did and next time they came with another comment asking:
"Calculate the hydraulic grade lines and give the actual flow rates for the 100-year event. What is the surcharged flow rate through the 6-inch outfall pipe from "8" to "Out"? (See attached #1)
My questions are:
1. In a conduit system with variable pipe sizes (not consecutive, ex. 8" --> 10" --> 36" ---> 6" --> outfall) how would be the HGL? I modeled this system in SSA (my very first time) and HGL was eventually dropping at the upstream nodes (see table in photo #2). We've been told that HGL will never drop at upstream in a conduit system, is it a rule?
2. If i'm right, the surcharging happens when the pipe capacity is smaller than what it should convey, right? Is it OK to have it in a system? In our design this pipe supposed to act as a restrictor, then what is the Surcharged flow rate? Is it the difference between peak flow and the capacity?
3. Any one can help how to model a similar system in StormCAD or SSA? I have difficulty when a small pipe connecting to a bigger size pipe but not a junction.
4. I'm attaching my drainage table (photo #2), is the actual rate the same as 100-yr partial flow rate? or what? I'm some how confused with "Design" , "Peak" and "Actual" flow rates definition. That could be because of my english, too!

Thank you so much in advance!

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