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.

MDSuDS provides a complete SuDS design and analysis solution for developers, planners, designers, engineers and consultants. It leads users through a design process for SuDS structures from conceptual design, including water quality, to hydraulic flow analysis. What's more, reviewing and comparing results for pre- and post-development scenarios can be conducted seamlessly.

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

Options modelled:

Two basic options for the Silva Cell System are discussed for modelling in MicroDrainage MDSuDS, 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. Input the Exceedence Level. This will be the base level of the ponding layer plus either 0.3m at maximum so to not surcharge the Silva Cell system.
2. Input the Base Level of the ponding layer within the Silva Cell.
3. The Freeboard is the level at which a flood risk will be reported and should be between a value equal to or less than the ponding layer depth. If the Freeboard value is equal to the difference between the Exceedence Level and Base Level, flood risk will be reported for any water on the surface.
4. Estimate the base area for the Silva Cell system in the first instance. This might have to be adjusted after the simulation to either prevent flooding or reduce costs.
5. Enter the length of the system. This should ideally be the distance between the inlet and outlet if present.
6. For design purposes, enter the slope of the site. This might be amended for construction is slope is to great and to prevent scour on the planting soil.
7. The Side Slope will be ‘0’ as the sides are also vertical within the ponding layer.
8. Calculate the Base Perimeter based on the Base Area and Length dimensions.
9. The Top Perimeter will be equal to the Base Perimeter as sides are vertical.
10. Enter the filtration rate into the top layer of soil. Estimate filtration rates are:

11. Enter details of the underdrain if present. 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.

12. 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:

13. Enter additional details about the ponding area.
14. Enter additional details about the filter area (soil layer).

15. Enter Silva Cell treatment efficiencies for desired pollutants. Example removal figures are given below.

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 MDSuDS 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].