drainage calculations for drywell

[bbakk]

Is there a standard way to calculate the drainage potential of a drywell given a vertical percolation rate (derived from the standard falling head test). In the past I have used just the bottom of the gravel band (gravel band usually 3' in diameter)
and also have used both the bottom of the gravel band (full area) and 1/2 of the side area of the drywell together (area times percolation rate for retention rate). Does anyone know if there is a standard method for the hydraulic analysis of drywells and or of a publication that describes the correct way to draw the flow net as applied to the drywell?

Thank you in advance,

bbakk.

 

[dicksewerrat]

I'd use the perc. rate for the virgin soils, not the gravel you install.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[bbakk]

Of course ... one should not use the perc rate for gravel (the gravel band serves as a medium between the drywell and virgin soils) ... a drywell typically is a perforated manhole with a gravel band surrounding it (2 to 3’ in diameter - most agencies require a solid bottom on the manhole so the only vertical perc is the bottom of the gravel band – outside of the manhole) ... it is my understanding that there is a difference between vertical and horizontal perc rate in soils (a big difference) ... so just calculating the surface area around the outside of the gravel band down along the drywell multiplied times the perc rate will yield an erroneous (high) infiltration value ... I am wondering if anyone knows of a standard modeling technique for drywells (and or a flow net analysis) ... sorry for being confusing.

Thank you,

bbak.

 

[CarlB]

I did some searching a few months back, found a few articles/papers/agency guidelines, but nothing that led me to a reliable design procedure. Maybe you will be more dilligent and come up with something. A few "hits" you could duplicate in a web search;

"Artificial recharge of groundwater: hydrogeology and engineering", by Herman Bouwer

"Studies on groundwater recharge through surface drains", by Satvinder Singh, MP Kaushal*, SD Khepar, Mukesh Siag and Ashok Yadav

 

[queque]

The local office of the Soil Conservation Service (NRCS) Agency should be able to provide that information . They are very concerned about using improper techniques for percolation testing of septic or dry wells. They have extensive experience in characterizing soil properties.