Trench Soakaway

Hi Mohammad,

Yes, SewerGEMS and SewerCAD both have the ability to model infiltration trenches. They can be modeled using one of the new element additions called low impact development (LID) controls.  This is the LID icon:

And you can read more about the low impact development (LID) controls from this wiki technote:

http://communities.bentley.com/products/hydraulics___hydrology/w/hydraulics_and_hydrology__wiki/10324.low-impact-development-lid

Regards,

Mark

 

Hi Mark,

you have mentioned that could be used in SewerCAD..!! I am asking for Storm Water system which I believe that should be part of StormCAD which we have rain data; I do not think SewerCAD is able to deal with rain water. I target to design storm water system using Soakaway. how is the configuration/Model the storm water going from manhole/gully  to the trench soakaway  and the dissipation into the ground (we do not have outfall)? 

Regards,
MO.

Mohammad,

SewerCAD does have the capability to model rainfall data. StormCAD probably would not be the program you want to use in this case because it's a steady state peak flow modeling software which means that you would not be able to look at the infiltration trenches  draining results over time.  

If you want to model this system what you would have to do is layout a catchment and then associate the LID control to that because LID controls need to have a what we deem a "parent catchment", which is just a catchment that is associated with the LID control.

The blue box that is outlined above is where you will click on the ellipsis to open the low impact development controls manager where you will create your LID (infiltration trench) control. The LID control manager can also be accessed from the Components menu. The wiki that I linked to in my previous post should explain a little more about these.

This catchment needs to be setup to use the EPA SWMM runoff method. You also need to make sure that whatever loss method that you decide to use in the catchment matches with the loss method that you have set in your calculation options under the "SWMM Hydrology" section or vice versa.

In order to get the flow from your upstream manhole into your catchment you will need to add a hydrograph type inflow wet collection on your catchment. You can get this information by modeling up to the manhole point in your model and ending it at a free outfall. After doing this you would run your model and right click on that outfall then select data table. Finally, you would copy and paste the data table values into the inflow wet collection hydrograph. This will simulate the flow coming from that upstream manhole and pass it to the catchment and will be flow in addition to the runoff you are getting from your catchment.

The final part of your model will be a free outfall that you will connect to your catchment as the outflow element. I know that you stated the infiltration trench will not have any outflow, but in order for the model to run SewerCAD needs an outfall and the catchment needs to have a downstream element. This outfall will just be in place to satisfy the requirement of the software and should not receive any flow if your infiltration trench is set up correct.

Your final model would look something like this:

I hope that helps out.

Regards,

Mark

Mohammad,

SewerCAD does have the capability to model rainfall data. StormCAD probably would not be the program you want to use in this case because it's a steady state peak flow modeling software which means that you would not be able to look at the infiltration trenches  draining results over time.  

If you want to model this system what you would have to do is layout a catchment and then associate the LID control to that because LID controls need to have a what we deem a "parent catchment", which is just a catchment that is associated with the LID control.

The blue box that is outlined above is where you will click on the ellipsis to open the low impact development controls manager where you will create your LID (infiltration trench) control. The LID control manager can also be accessed from the Components menu. The wiki that I linked to in my previous post should explain a little more about these.

This catchment needs to be setup to use the EPA SWMM runoff method. You also need to make sure that whatever loss method that you decide to use in the catchment matches with the loss method that you have set in your calculation options under the "SWMM Hydrology" section or vice versa.

In order to get the flow from your upstream manhole into your catchment you will need to add a hydrograph type inflow wet collection on your catchment. You can get this information by modeling up to the manhole point in your model and ending it at a free outfall. After doing this you would run your model and right click on that outfall then select data table. Finally, you would copy and paste the data table values into the inflow wet collection hydrograph. This will simulate the flow coming from that upstream manhole and pass it to the catchment and will be flow in addition to the runoff you are getting from your catchment.

The final part of your model will be a free outfall that you will connect to your catchment as the outflow element. I know that you stated the infiltration trench will not have any outflow, but in order for the model to run SewerCAD needs an outfall and the catchment needs to have a downstream element. This outfall will just be in place to satisfy the requirement of the software and should not receive any flow if your infiltration trench is set up correct.

Your final model would look something like this:

I hope that helps out.

Regards,

Mark

Thank you Mark - just few clarification needed in your answer:
1- getting the information by modeling up to the manhole point ending it at a free outfall is to be done in StromCAD or in SwererCAD (we suppose to use Rational method for model piping and gullies).
2- you mentioned : "catchment needs to be setup to use the EPA SWMM runoff method"; can I stay with Rational Method or it must EPA SWMM? and for that configuration The parent catchment is the Soakaway area (because the trench is under parking and there is no surface flow into it; the flow from the direct connection)
3- you also mentioned: "should not receive any flow if your infiltration trench is set up correct" would you please let moe know how? the trench in the program talks about gravel layers while I have Poly Storm Cells of soakawaies.
4- providing sample model example will elaborate more and support us.

you are so apprecaied.
MO.

Mohammad,

1) It would have to be done in SewerCAD using an EPS run, so you could get hydrograph flow over time at the outfall and enter that as your inflow wet collection into the catchment.

2) You'll need to use the EPA SWMM runoff method for the catchments using the LID controls. You can use runoff methods on your other catchments if you like. If the parent catchment for your LID control would be your soakaway area then you can make sure that catchment is the exact size of your trench and set the option in the LID control for "Occupies Full Catchment?" to True.

3) When I made that statement I was keeping in mind what you stated previously where you said, "I target to design storm water system using Soakaway. how is the configuration/Model the storm water going from manhole/gully to the trench soakaway and the dissipation into the ground (we do not have outfall)? ". If you don't have an outfall I assumed that there is not flow leaving the infiltration trench because otherwise you'd have an outfall. Therefore, if the trench properties were setup with high porosity and a large enough capacity you shouldn't have any flow leaving. The input for those numbers would vary based on your design and are a different for every system, so I can't provide you with more information than that.

What's the name of the property that you are referring to when you're talking about the 'gravel layer'?

4) You can download a sample file here:

bentley.sharefile.com/.../s3b7cfb465b14ccf8

Regards,
Mark