What is Silva Cell?

The DeepRoot® Silva Cell® is a patented, modular, suspended pavement system that integrates water, soil and tree roots and delivers on-site stormwater management through bioretention. DeepRoot’s Silva Cell system can be designed for surface water management by constructing a bioretention system within the Silva Cell modules. A typical bioretention system consists of:

·       A ponding layer to store surface water runoff prior to treatment through the treatment media

·       Treatment media which filters the surface water and removes solids, organic and non-organic particles

·       Aggregate storage to convey the treated flow to the outlet or stored before infiltration to the surrounding soil

·       An overflow structure to prevent surface flooding during exceedance conditions

How can it be modelled?

Innovyze’s MicroDrainage is an ‘advanced drainage design software that optimises the performance and effectiveness of drainage systems, including SuDS – both greenfield and retrofit’. MicroDrainage allows for a number of SuDS features to be included within a design, including bioretention systems allowing the user to design for attenuation and infiltration.

For more information and support with MicroDrainage, please visit www.innovyze.com.

Options modelled:

Two basic options for the Silva Cell System are discussed for modelling in MicroDrainage, one is the Silva Cell 2X option and the second is the Silva Cell 3X option (shown below). Both systems have a similar make up of layers within the Silva Cell, but vary in the overall depth of the system.

Design steps:

1. Select if the Silva Cell is a ‘Flow through structure’. Tick box if the Silva Cell will have an underdrain, untick if the Silva Cell is at the end of the drainage run and being used as a soakaway.
2. If allowing infiltration from the Silva Cell, enter infiltration coefficients from infiltration report.
3. Enter the porosity for the Silva Cell for the ponding layer within the crate system. This value will be 0.92 in both cases for the Silva Cell 2X and 3X systems.
4. Enter details of the underdrain if required. The underdrain is recommended if there is the likelihood of the Silva Cell becoming saturated or submerged for long periods which can be detrimental to a tree’s health.
5. Enter the overall dimensions of the Silva Cell System. The depth of the system will be either 784mm or 1,092mm depending whether the 2X or 3X system, respectively, has been used. The area should be estimated in the first instance and might have to be adjusted after the simulation to either prevent flooding or reduce costs.

6. Enter infiltration information for the layers within the Silva Cell as indicated in the Silva Cell 2X and 3X sections. Depths for the layers are indicated above and suitable estimate filtration rates and porosities are shown below for the different soil types that might be installed:

Once the information is input, you can run simulations of the drainage design and optimise the size of the Silva Cell system.

Data from DeepRoot

DeepRoot have created a Stormwater Design Tool which can be used to estimate the size of your Silva Cell system before entering it into your Flow software. It can also be used after modelling to understand the number of Silva Cell modules required for the area of bioretention required.

Support

For additional support from DeepRoot, please refer to our resources section for more information on the Silva Cell or contact [email protected].