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MaterialPorosity (%)Typical Conductivity (m/hr)


40 - 55<1<0.1
Sand35 - 505 - 50
Gravel / Crushed Stone10 - 3050 - 250500
Porous Concrete10 - 30200 50 - 300500
Rubber (Shredded)40 - 50300+
Crates/Lined tank90 - 100100 - 1000500+


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.


titleClay content

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.
Please refer to pages 146-148 of the SWMM Reference Manual Volume 1, for example.

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.
It would not be appropriate to represent such a layer using the Storage layer.


Gravel, Crushed Stone and Rubber -