Device routing for Multiple ponds in series 2

[notsocivil]

Hi all,
I am trying to model a basin that is divided into three separate basins by 2 concrete walls. Think of a rectangle divided into three equal areas. The walls will have small orifices so i can get my water quality and then have weirs on top for quantity. The last basin (#3) will have the outlet structure. I have my subcatchment going to basin 1 which is routed to basin two and basin two is routed to basin three.

Starting from basin 3, the outlet structure has a culvert discharging to an existing storm system. The culvert routing was selected as the primary and then my orifices in the outlet structure were selected as device 1. As I work my way back to the wall separating basin 3 and 2 with orifices and a weir, should I route the orifices in the wall as devices or primary to get an accurate model?

Thanks in advance.

 

[psmart]

If I understand correctly, the orifice and weir are independent devices discharging into the next pond. In this case, each device would use the (default) primary routing.

Other routing options are used only when one device is placed before another, such that it could restrict the flow. This seems to be the case with your double orifice before the culvert. For an example see

http://www.hydrocad.net/pond1.htm

 

[notsocivil]

Thanks for the info psmart.

I am modeling my system using the modified rational method and basically have a subcatchment discharging to pond 1, then pond 1 to pond 2 and pond 2 to pond 3 then to my outlet structure. I double click my subcatchment node and update the critical duration analysis then check my hydrograph for pond 3 and I get a discharge. But when I update the critical duration analysis for my pond 3 node I get a drastically different discharge. Which discharge is correct?

thanks....

 

[psmart]

They are all correct... You are seeing some of the complications of the rational method, and why it is not recommended for pond calculations.

The critical duration analysis determines the rainfall duration (and corresponding intensity) that causes the worst-case condition at the selected node. For a subcatchment, the critical duration will be equal to the Tc, in order to generate the highest peak flow. But for a pond, a longer duration is generally required to achieve the maximum water surface elevation and corresponding maximum discharge.

For further details, please click the help button on the report. Also see

http://www.hydrocad.net/rational.htm

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[notsocivil]

thanks again for the information. I would prefer to use the scs method but its a tight site and the county prefers rational.