Infiltration Trench

[Sathre]

Does anyone have a good way to model a sloped infiltration trench? I have a 5 ft wide trench, 3 feet deep with, 300ft long at about 1.5% slope. Do you just set up the model with multiple custom stage storage? Do you need to have some sort of outlet from each storage to the next?

 

[psmart]

How are you planning to model the trench? If you're using a pond, you could use custom storage, but an easy "trick" is to use the pipe storage option with a 5x3 box.

However, your slope of 1.5% over 300 feet means that the trench drops 4.5 feet over it's length. Since the drop is greater than the nominal 3 foot depth, you really only have 3 feet of available depth (at the low end) tapering to zero depth after 200 feet. The remaining 100 feet will never hold any water - assuming a level water surface.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[msquared48]

Is the extended length intended to be a reserve?

Mike McCann, PE, SE (WA)

 

[Sathre]

No, the extended length is to catch runoff. I am running the trench across the rear yards of 7 lots in a new development. I had modeled the trench as a pipe with void storage over the 3 ft depth (20%) and then an additional pipe storage above that of 1ft with 100% voids for live storage. So a small infiltration trench / ditch.