---
title: "Guidance on Conductivity Rates"
canonical: "https://help.innovyze.com/space/infodrainage2020v2/16417073/Guidance%20on%20Conductivity%20Rates"
format: markdown
---
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)** |
| --- | --- | --- |
| Clay | 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 |

> ℹ️ **Warning**
> ℹ️ 
> ℹ️ 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.

> ℹ️ **Clay content**
> ℹ️ 
> ℹ️ 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.  
> ℹ️ Please refer to pages 146-148 of the [SWMM Reference Manual Volume 1](https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P100NYRA.txt), for example.
> ℹ️ 
> ℹ️ 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.  
> ℹ️ It would not be appropriate to represent such a layer using the Storage layer.

### References:

Crushed Stone and Rubber - [https://vtrans.vermont.gov/sites/aot/files/highway/documents/materialsandresearch/completedprojects/AOT_PermeabilityofHighwayBaseandSub-baseMaterial.pdf](https://vtrans.vermont.gov/sites/aot/files/highway/documents/materialsandresearch/completedprojects/AOT_PermeabilityofHighwayBaseandSub-baseMaterial.pdf)