The conductivity rate is used for the calculation of both the horizontal and vertical transfer of the water in the sub-surface layers of a Stormwater Control.
The rate to be used would typically be specified by the manufacturer/supplier of the aggregate material being used in the system.
However a table of representative values for different materials found in scientific reports and manufacturer documentation is provided below.
These values are only indicative and should be used with caution.
|Material||Typical Porosity (%)||Typical Conductivity (m/hr)|
|40 - 55||< 0.1|
|Sand||35 - 50||5 - 50|
|Gravel / Crushed Stone||10 - 30||50 - 500|
|Porous Concrete||10 - 50||50 - 500|
|Rubber (Shredded)||40 - 50||> 300|
|Crates/Lined tank||90 - 100||> 500|
Conductivity and Porosity values of a Soil can vary widely between sites. You may need help from a Geotechnical Engineer for evaluating the appropriate values on your site.
Note that the Porosity of a Clay can be larger than that of a Sand, but the Drainable Porosity of the Clay is much lower than that of the Sand, because the Field Capacity of the Clay is much higher than that of a Sand.
Therefore a soil layer with a significant content of Clay can only be represented properly using the Soil layer (Filtration Layers tab), where the Field Capacity and Wilting Point values can be specified.