Utility Vault Sump

[TLHS]

I've seen utility vaults and similar structures in the past that have a drain hole in the bottom and a sump area underneath made from drain rock that acts to hold water and allow it to seep into the surrounding soil. This seems like a neat solution to water collecting in small structures like that and it seems like it should work as long as you're above the water table, but I've never seen anyone actually try to size them rationally.

Does anyone have experience with something like this, or a good idea of how to approach the problem. I'm always wary of using things if I can't back them up properly. I assume I should be able to determine a reasonable size using steps similar to:

1) Size the area such that the voids hold maximum daily/weekly/whatever fluid inflow
2) Ensure that seepage into surrounding soil is such that inflow rate over a certain amount of time is equal to or less than the outflow rate.

The problem is figuring out number 2. It seems like it should be a one dimensional flow type of problem, but if I'm above the water table and don't really have a depth of earth I'm specifically trying to drive the water through I don't really know how to establish the hydraulic gradient I'd need to work through the problem.

Any thoughts?

 

[beej67]

Depends on where you're at.

The SFWMD Basis of Review has some guidance for stormwater infiltration methods that's pretty well tested, since they've been using stuff like that for decades in South Florida. You may also be able to wrangle up some engineering methodology for BMPs such as rain gardens or infiltration trenches out of the Georgia Stormwater Management Manual or the NCDENR Dept of Water Quality BMP Manual.

Googling those might get you started.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[TLHS]

Thanks,

Once I knew the term infiltration trench it gave me things to search for. There is a significant amount of literature on the subject and I was able to find more than enough literature that I'll be able to come up with a reasonable design method for sizing and specifying things of this sort.