## 2 Materials and Methods
### SuDS Interventions  
Following the recommendations in the Surface Water Management study [39], a soft market event was held by Durham County Council (DCC), Environment Agency (EA) and The Water Hub ahead of an invitation to tender (ITT) for a programme of work to build and monitor SuDS features [35]. The ITT called for respondents to adopt a collaborative and community-centred design approach, engaging with local residents, SMEs and the existing consultants and partnerships from previous studies (e.g. [35; 39]) to design and install: an innovative SuD Tree system on Poplar Street, an affordable rainwater harvesting system for rear yards and a smart monitoring system to quantify the performance of the scheme. A consortium of businesses were selected to deliver a range of interventions, designed to mimic a typical programme of SuDS as frequently implemented by practitioners. The interventions included two SuDS tree pits, four street trees and two rear-yard rainwater attenuation planners (Figure 3). These SuDS features were designed to complement existing rain gardens, porous paving, and feature paving that had been installed in Pine Street, following the South Moor Surface Water Management plan [39].  
The two SuDS tree pits were installed in Poplar Street. A 43 m\({}^{3}\) trench was excavated to construct the two tree pits. This trench was lined with a porous geotextile membrane and GRN20 plastic reinforcing mesh using a modular cell system (RootSpace, GreenBlue Urban, UK). This load-bearing soil support system was designed for maximum soil and rooting volume in the tree pits (Figure 4A).  
Figure 3: The location of three monitoring points (M), two rear yard planners (blue squares), four street trees (green circles) and two sustainable drainage systems (SuDS) tree pits (green circle with black edge) on Pine Street and Poplar Street (not to scale). The dashboard interface was installed in The Haven Community Centre (H).  
Fifty tonnes of Hydrosoil mix was installed, designed to withstand frequent short-term water logging. A SuDS filter drain was then installed and connected to the existing drainage chamber. Inlets were installed to allow surface water to pass through the tree pit (ArborFlow, GreenBlue Urban, UK). A double inlet irrigation and aeration system (RootRain Arborvent, GreenBlue Urban, UK) was installed to maintain long-term soil health (Figure 4B). Trees were planted and supported by a tree grille and frame (ARBPC1507A, GreenBlue Urban, UK), and protected from road traffic by bollards. Four street trees were installed in Poplar Street, either side of the SuDS tree pits, to further break up the hard standing.  
Two rainwater attenuation planners were installed in the rear-yards of Poplar Street to disconnect two downpipes and capture the roof run-off (Figure 5). These planners reduce and slow the flow into the drainage network, reducing the likelihood of the system becoming overloaded. Each planter consisted of a premium quality timber base with a double-wall construction and guaranteed watertight liner (Sudsplanter Ltd., Bradford on Avon, UK). The planter contained layered growing media and filter materials to provide water and nutrients for the plants; and filter and attenuate flow. After filtration and absorption by the plants, any remaining water is collected in a high-volume, high-strength reservoir at the base of the planter, enabling storage for re-use or slow release into the drainage network. Integral flow control ensures a precise discharge rate, whilst a high-level overflow controls water levels during extreme rainfall.  
Figure 4: Photographs of the installation of two tree pit sustainable drainage systems (SuDS) in County Durham, including: (**A**) modular “RootSpace” cell system and; (**B**) one of the tree pit’s aeration vents.  
Figure 5: Schematic of the rainwater planners installed in two rear-yards on Poplar Street. Each planter contained a filter medium and storage compartment to filter and attenuate roof run-off and reduce flow into the drainage network.