Trent Rivers Trust commissioned the project in order to create a flagship space that could demonstrate the benefits of SuDS to the local community. As a demonstration site, it was important to provide a wide variety of possible SuDS features: domestic features near the caretaker's house could show what was possible on a small scale, while larger scale amenity benefits could be seen in the lower, more expansive parts of site.
The design was also intended to relieve pressure on the creaking Victorian sewer systems. It could do this by providing natural means for water to infiltrate, as well as holding back larger flows before the sewer, reducing flood risk and water quality issues in the nearby River Derwent.
It was also agreed that a variety of habitats could be provided, beyond simple mown grass, and as such the ecological health of the site could be improved.
Finally, as a a listed building, the Strutts Centre would require a landscape design to complement existing materials and architecture.
The historic buildings of the Strutts Centre required a sensitive approach. The blue engineering brick channels alongside the caretaker’s house are a repetition of the brick used elsewhere, while stainless steel outlet spouts lend a subtle modern addition.
The volunteers and trustees of the Strutts Belper centre played a central role in the formation of this design, and an enthusiasm for gardening has been reflected in the project’s use of perennial planting. A mix of blue and white annuals denotes the principal flow route that run-off will take on site: a use of colour that mimics the water flows. Along with the perennial planting, an annual ‘nurse crop’ was sown in order to protect the soil and add early colour.
The site slopes gently towards the River Derwent – the floodplain of which is visible from site – and it was decided that this visual link could be emphasised by selecting appropriate plant communities, and by echoing the forms of the nearby river in the design of channels. It was suggested that elements of river morphology could be used artistically: river-worn boulders could be used in channels, not only to prevent erosion, but also to depict the deposition of a typical river bend.
Habitat-friendly planting was used in order to complement the plant communities of the nearby floodplain: native wildflower mixes provide height and interest in hard-to-mow areas, while adding valuable habitat for invertebrates that was previously lacking.
The site was divided into two key catchment areas:
The Caretakers’ House
The compact arrangement of downpipes and paths around the property are reworked to turn the run-off from the roof into the primary input to the raingarden. This feature is a linear raingarden: a long, mostly level channel with a series of low weirs that hold back flows, ensuring that smaller rainfall events are taken into the ground. In heavy and prolonged rainfall events, beyond the 1 in 10 year likelihood, the raingarden can overflow gently downslope towards the lower main basin.
The Main SuDS Basin
This basin stores rainwater that comes from a roof area of 165m2 and a tarmac area of 465m2 is a large elliptical basin with the capacity to store up to 17m3: a volume which will store up to the 1in10 year rainfall event. The controlled release of 17m3 of rainwater through a limiter will make a significant difference to the locally overburdened Victorian sewers.
This primary basin is fed by a meandering ‘collector’ channel: a serpentine channel that picks up the various inputs detailed below, and provides a first round of cleaning for the more polluted run-off from the car park.
Water from the roof falls inside the existing cast iron downpipes, but instead of dropping straight to the sewer, it is taken in two underground pipes (the fall back towards the building on the tarmac above did not permit surface flow), through a low wall, and into the primary basin via two stainless steel spouts that adjoin the collector channel.
Water from the tarmac parking and driveway (as well as potential overflow from the linear raingarden above) is collected in a large capacity channel drain, which releases into the collector channel.
A long straight swale is designed to run along the face of the Strutts building: this will pick up run-off from the large area of tarmac between the building and grass. This swale is designed to pass through the low wall in a stainless steel ‘letterbox’ structure, before dropping into the basin.
Location : Belper, Derbyshire
Return Period Attenuated : 1 in 10
Techniques : Channel Drains, Channels, Swales, Basins, Raingardens.
Discharge Destination : Sewer
Discharge Flow Rate : Greenfield Runoff Rate
Client : The Trent Rivers Trust