 # CivilStorm weir loss is not correct in my model

I am using CivilStrom (Implicit SewerGEMS Dynamic Wave solver) for my model. After checking the results I have realized that the weir losses calculated by the program does not match the manually calculated one although I am using in my manual calculation the same equation the program is using. Can you please advise what is the reason behind that difference?

As per the program the weir is placed on the down stream of CO-110 and has the following properties @ Time 0.95:

1- Weir elevation = 98.300 m

2- Weir length = 1.9 m

3- Weir Coefficient = 1.84

4- Flow at Time 0.95 ~ 940.121m3/hr

5- Hydraulic grade line (out) = 98.6249 m

Which means that as per the program the Water depth above the weir (Weir losses) = 98.6249-98.3=0.3249m

As per manual calculation using the same equation the program is using: 940.121/3600 = 1.84 x 1.9 x h^1.5

h^1.5 = 0.747 >> h = 0.175m

If we compare the program calculated losses of 0.3249m with the manually calculated loss of 0.175m we can see a big difference of around 80% extra loss !

I know that if we have one weir in the whole model it might not be a problem but imagine having a couple of weirs in the model, then we can have a serious issue.

Can you please explain from where this difference is coming?

I have attached the model for your reference0508.Using the - Implicit (SewerGEMS Dynamic Wave) - solver 1.zip

• Hello AMR,

We will go through this and get back to you.

Regards,

Sushma Choure

Bentley Technical Suppport

• • • Amr,

Stop control structures are more difficult for the numerical solver to calculate compared to start control structures (see note in this article). If you place your weir as a start control structure on the next downstream conduit CO-121, you will get the expected head across the weir. Or, if you keep it as a stop control structure on CO-110 and increase the LPI coefficient (in the calculation options) to a value of 12, you will also get the expected head across the weir.

Regards,

Jesse Dringoli
Technical Support Manager, OpenFlows Products
• • • • • 