sample way to design a detention pond ?

Hello Mahmoud,

I will answer your queries point-wise;

mahmoud mahmoud said:

i have an open channel with certain flow and i want to detent some of this flow and then drain the rest to the drainage net work

For the above scenario, do you wish to divert the flow "before" it enters the pond or "after" the pond (exit of the pond). If you have to divert only part flow to the detention pond you need to have a control structure at the inlet such as a weir to divert flow to the pond.

mahmoud mahmoud said:

what is the solver should i use ?

This depends on what conditions you wish to model. In SewerGEMS you can use the different solvers Implicit / Explicit / GVF-Rational and GVF-Convex based on your requirements. However, the use of these solvers changes for how you are modeling the pond outlet structures. The differences in how outlet flow is calculated depending on the solver used is illustrated in the article below;

Pond and pond outlet assumptions in StormCAD, SewerGEMS, CivilStorm and SewerCAD

mahmoud mahmoud said:

how to model the flow ( should i model the catchment area or should i use inflow input for the pond as hydrograph ...........?

If the source for your flow for the open channel is a catchment, then you can model the necessary storm event to simulate runoff generated which will be captured by the open channel. Alternatively you can also specify an inflow hydrograph if you already have the flow data from the catchment outlet.

mahmoud mahmoud said:

what should i use for  pond out let structure ?

You can use a weir, orifice or any other type of control structure. You should look at what you wish to achieve and your site conditions.

mahmoud mahmoud said:

down stream pond out let structure what should i use ( pipe or open channel ....) to deliver the remaining flow to the outfall>?

Again this depends on your project considerations. You can choose either, except that in case of excess flow there will be overflow in the channel whereas the conduit / pipe would be surcharged.

You can try the PondMaker tool in SewerGEMS to design your detention pond - Using PondMaker

Hope this helps.

thanks a lot sir,

"For the above scenario, do you wish to divert the flow "before" it enters the pond or "after" the pond (exit of the pond)."

after >>> i already now the area of the pond >>> h want to know what this area (volume) can take from my flow ? and determine the bypass flow after detention >>> so i can design the down stream structures 

Hello Mahmoud,

Typically, the pond would be sized so that inflow would not overtop the pond while flow is leaving the pond through the outlet structure. Are you planning on designing more than one composite outlet structure for the pond?

Regards,

Scott