The Rainpark was the largest of three SuDS interventions along the A504 Priory Road, Hornsey. As a public park, used often by the Primary School that fronts onto the park, the priority was to maintain, and enhance the useable space by developing a SuDS scheme here.
Anecdotal evidence of flooding at the adjacent roundabout was widely mentioned, and anticipated flows at this point intersection (at the base of significant inclines and adjacent greenspace) were high.
Water Quality was the principal driver for the Priory Road projects, in an attempt to highlight, and improve the water quality of the Moselle. The River Moselle runs culverted, almost directly below the park in the South West corner.
SuDS can create diverse, interesting landscapes. The landscape was to be fun and thought-provoking for children, as well as for adults. Defined by undulating play elements, biodiverse meadows, and clear signaling of the flow-route, the scheme was intended to be legible and colourful. Robust, trafficable elements were needed to collect significant volumes of runoff from the Priory Road, while maintenance of the features, together with more conventional maintenance tasks, was a consideration from the conception of the scheme.
Extensive anecdotes told of flooding at the roundabout adjacent to the park. As such, the kerb inlets needed to manage high flows, sheeting across the carriageway in times of high rainfall, in order to safely remove the water from the roadside. The scheme could therefore bring an additional local benefit by removing this ponding at a critical junction.
The project aimed to enhance the park for people of all ages, while paying particular attention to the needs of the children of the adjacent school. Green oak balance beams were designed to run from the upper shoulders, across the shallow basin, and back to dry ground. Rarely would there be any water in the basins - the chance of crossing over water is only fleeting.
The existing park layout, combined with the inlet areas available, lent itself to a clear SuDS strategy. The park was effectively divided into an East side (Catchment ‘A’) and a West side (Catchment ‘B’). Each side had it’s own road catchment area to manage, and these remain separate at all times.
In order to maintain as much dry, useable space as possible, the two basins that receive flows directly from the road (A1 and B1) were given ‘underdrains’. These are effectively French Drains, connecting to Flow Control Chambers (see video), and they ensure that any residual dampness is quickly removed. This was to ensure that little muddy footprints wouldn’t plague the school caretaker…
Several trees had been recently planted, including one memorial tree. Each tree was carefully considered, and a design approach was taken that created ‘islands’ from the root-protection areas beneath the crown. This is perhaps most evident in Basin A2, to the East, where several tree ‘islands’ are within the basin, and several others are creeping into the basin sides.
In order to maximize the useable space, the scheme proposes that the two rear basins (A2 and B2) would remain as mown grass, and be wide, shallow features. This way, the school could still use these areas as performance/stage areas during their summer concerts.
The same strategy applies each catchment: Kerb Inlets take water below the pavement and into vegetated pre-treatment areas. After this pre-treatment, the first storage features, closest to the road, are capable of holding volumes up to the 1:30 year event. As mentioned, these basins are underdrained: meaning that the water drains through a typical trench drain construction. A flow control chamber restricts release of water from the basin. These 1 in 30 basins can overflow at the surface, to storage basins capable of holding the 1 in 100 (+30%) for their catchment area.
In Catchment A, a 15 metre swale cleans the water coming into the park from the road surface. It is then admitted to Basin A1 – three small basins, joined by a flat base, to form one storage unit.
Overflow from Basin A1 is via a grassed channel, and through the tarmac path via a pavement bridge. The bridge opens out onto Basin A2 – a shallow SuDS landscape of tree ‘islands’ among mown grass.
In Catchment B, pre-treatment is delivered within a short swale, and the opening to the basin. This is a lower area at the inlet to the basin, separated from the ‘main’ basin floor by large boulders, to allow for settlement and separation of the road silts.
After this, storage for the 1 in 100 + 30% is provided below the canopies of more mature trees, closer to the school. Again, overflowing water has to cross the path via a pavement bridge, prior to reaching this final storage area. The storage medium was created here by the use of a 200mm high bund, surrounding slightly sloping ground, and therefore achieving storage behind the bund.
Location : Hornsey, North London
Return Period Attenuated : 1 in 30 and 1 in 100 + 30%
Techniques : Kerb inlets, infiltration basins, underdrained basins, biodiverse meadows, flow control chambers, and swales.
Discharge Destination : Surface Water Network
Client : Haringey Council/Thames21