UK Superstore Overcomes Two Obstacles at Once with Silva Cells

Car park tree canopy is thriving thanks to DeepRoot Silva Cell system and its soil volume and stormwater management benefits

Overview

As project plans for the new Lidl Superstore in New Milton, UK, were put together in 2010, developers knew they wanted to incorporate a tree canopy in their car park as both a welcoming aesthetic for customers and to disrupt the area’s heat island effect by providing accessible shade. When onsite stormwater management also required attention, developers turned to the DeepRoot Silva Cell system as a simultaneous solution for many of their green infrastructure challenges.

Installation Summary

Number of Silva Cells: 339 frames

Trees: 5

Soil Volume (Total): 99.92m³

Soil Volume (Per Tree): 19.98m³

Watershed Area: 799.36m²

Watershed Storage: 19.98m³

Type of Project: Large trees and stormwater

Project Designer: LHC & HTS

Project Council: New Forest District Council

Installation Date of Silva Cells: October 2010

The Project

To ensure an enjoyable customer experience, project planners at the New Milton Lidl Superstore integrated an urban forest into their car park design from the beginning. Alleviating the heat island effect, often encountered in shade-less car parks, was a top priority — but developers were also subject to a mandate put in place by the New Forest District Council which required a minimum of 20 cubic metres of lightly compacted soil per tree. Another element of the project was how to manage onsite stormwater, including rainwater coming off the roof of the 800 cubic metre superstore.

Many developers would approach these obstacles individually, as separate issues that required separate solutions; however, the project design team at LHC recognized the opportunity, utilizing the DeepRoot Silva Cells to address multiple green infrastructure concerns simultaneously.

DeepRoot Silva Cell Success

The 339 Silva Cell frames installed in the Lidl Superstore car park provide adequate soil volume for healthy growth of the 5 London planetrees while also treating at-source stormwater. A total of nearly 100 cubic metres of soil are contained in the planting area, almost all of which is located underneath the car park. Each tree — which, at the time of planting, measured 7m tall and 30-35cm in trunk diameter — has access to an appropriate amount of soil volume, allowing each one the opportunity to grow large, healthy tree canopies.

Likewise, water from the facility rooftop routes through the soil, first entering a back inlet gully pot to help dissipate the energy before being piped to the cells. (This also serves as a backup system should the Silva Cell area become overwhelmed — if the water backs up to this gully, it sheds into the car park and enters the conventional sewer system.) During a normal rain event, the water passes through the cells into a holding tank. If a critical water level is reached inside this tank, it automatically pumps from the tank directly into the local sewers.

Lidl Superstore developers found that this dual-solution Silva Cell system enabled them to maximize the number of parking spaces while also incorporating trees. Front-end cost savings were also realized as the water-handling capability of the Silva Cells allowed planners to downsize water attenuation systems elsewhere on the site.

Environmentally, the design will have a significant impact on its community: shedding water into the Silva Cell system permits regeneration of the water course and slowing the stormwater drainage will have powerful effects downstream, helping to avoid flooding and non-point-source pollution, thereby improving the quality of adjacent water bodies. The increased size and health of the trees in the car park, similarly, act to improve air quality and reduce heat island effect.