exfiltration in hydrocad

[dumaszarktek]

How do I use my perc test data? I understand the "pond outlet device" and "discarded" Can I use ft3/ft2? for soil percolation rate?

I am designing a drywell system for a residence. I am an architect so not my main line.

Thanks
Dave

 

[psmart]

Yes, you can convert the perc rate to an equivalent velocity, but you also need to use you judgement to determine that the entire (larger) pond will behave according to that value over an extended period of time.

From the HydroCAD help system:

Using a percolation rate

A measured perc rate can be converted to an equivalent exfiltration velocity by the following equation. However, other factors must be considered to determine if this is a reasonable design value for a proposed exfiltration area. (For example, can a large pond be expected to perc at the same rate as a small test pit over a period of many hours?)

V = 60 / P where:

V=Exfiltration velocity [inches per hour]
P=Perc Rate [minutes per inch]
60=Units conversion factor

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[dumaszarktek]

thanks for your reply!

I had an 8" dia perc hole, the sides were lined with a metal sleeve, the final hour test was a 10" drop. Do i use 10"?

also is it possible to enter a clogging factor?

If i have a battery of Cultec 330 XLD chambers with an invert of -4', Do I want to size my pond such that the water rise maxes out at about -1'?

Thank you.

 

[psmart]

You will have to determine the exfiltration rate that is appropriate for your purposes. You could reduce the discharge multiplier if you want to allow for "clogging", or just use a lower exfilt rate.

Again, you will have to determine the appropriate peak WSE for your specific situation and design goals. There is no single answer. It all depends...

I'll leave it to the seasoned H&H engineers on the forum if they want to offer more detailed design guidance, but I'm going to limit my comments to specific modeling issues.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Twinkie]

With prefab chambers you can design storage above the chamber in the stone, you aren't limited to a specific elevation.

But as Peter said....it all depends on what you're trying to do.