Permeability – the rate at which a fluid flows through a porous substance under given conditions.
Porosity (void space) – the portion of a volume of material that is not solid.
Infiltration – movement of a fluid into the surface of a porous substance.
Infiltration and Permeability are used interchangeably in reference materials. For runoff coefficient, click here (pdf).
The Permeability (infiltration) of Grasspave2
Sand permeability = 8.27 inches/hour
Grass in Sand root zone= 9 to 25 inches per hour (various USGA mixes)
Base course poor draining = 2.63 inches/hour* (sandstone with 10% fines)
Base course common = 7.37 inches /hour* (limestone with 3% fines)
Base course mixed = 38.55 inches /hour***** (66% GP and 33% GW)
Subsoils need to infiltrate at least 0.5 in/hr to be considered permeable** and recommended soils would be loam, sandy loam, or loamy sand.
Our system would deliver 2.63 to 38.55 inches of water per hour to the subsoils.
The Permeability (infiltration) of Gravelpave2
Open graded aggregate, 1/4” = 2500 inches/hour***
0.1” to .2” inside open-celled grids = 40+ inches per hour****
Base course poor draining = 2.63 inches/hour* (sandstone with 10% fines)
Base course common = 7.37 inches /hour* (limestone with 3% fines)
Base course mixed = 38.55 inches /hour***** (66% GP and 33% GW)
Subsoils need to infiltrate at least 0.5 in/hr to be considered permeable** and recommended soils would be loam, sandy loam, or loamy sand.
Our system would deliver 2.63 to 38.55 inches of water per hour to the subsoils
The Porosity (void space) and Water Storage of Grasspave2
13 inch cross-section
One inch Grasspave2 with Sand = 20% void
12 inches base course = 20% void (16%-and-up depending on composition)
13 inches x approx. 20% void space =
2.6 cubic inches of Water Storage
The Porosity (void space) and Water Storage of Gravelpave2
13 inch cross-section
One inch of Gravelpave2 with Open Graded Aggregate at 3/16” – 3/8” = 35%
12 inches base course = 20% void (16-35% depending on composition)
(One inch x 35%) + (12 inches at 20%) =
2.75 cubic inches of Water Storage
Download a pdf of this information
GW = Well graded, clean gravels, gravel/sand mixtures
GP = Poorly graded, clean gravels, gravel/sand mixtures
All rates are approximate and actual installed rates will vary depending on local materials and other conditions.
If existing site soils infiltration rates are below .5 in/hr (silt loam, sandy clay loam, clay loam, silty clay loam, sandy clay, silty clay, or clay), additional drainage is recommended below Grasspave2 and Gravelpave2.
