Permeability
Permeability
(OP)
I need to design a temporary parking lot using a permeable material on top of a crushed stone bed. I am using underdrains since the subgrade is clay, and there will be virtually no infiltration.
My question is, how do I calculate the velocity or volume of water passing through the stone, assuming the surface material is 100% permeable? I have to prove to the City that the runoff from the site will not increase if we use this design.
My question is, how do I calculate the velocity or volume of water passing through the stone, assuming the surface material is 100% permeable? I have to prove to the City that the runoff from the site will not increase if we use this design.





RE: Permeability
RE: Permeability
RE: Permeability
Ishvaaag, the City will require storm water detention unless we can prove that the installation will not increase runoff from the site. My client does not want detention. I'll run the numbers and let the chips fall where they may.
RE: Permeability
I have just recently made a MODFLOW model to solve this problem. If you use the actual permeability for 57 stone, you can't believe just how fast this takes place. That said, there is no "simple" Darcy solution in the form of Q=kia that'll get it done. There's some integril to worry over, that's one thing I'm sure about!
Good luck.
f-d
¡papá gordo ain't no madre flaca!
RE: Permeability
A method I used to approximate a small parking area at my office, using brick pavers as a surface over sand, over gravel over clayey soil was to provide enough 'immediate storage capacity' by filling the sand & gravel voids with the precipitation. I adjusted the sand & gravel thickness to account for the precipitation volume. After running out a numeric analysis, above method provided a somewhat conservative but reasonable approximation FOR A SINGLE STORM EVENT.
The only reasonable numeric analysis I am familiar with is SEEP/W or a similar program specifically designed for water movement in soil. The very permeable stone will complicate the analysis. I have used SEEP/W to size Storm Water Retention Ponds to achieve partial or complete drainage and to approximate drains behind MSE retaining structures while checking for global stability. Can be very complicated.
RE: Permeability
RE: Permeability