Making the Most of SuDS with Controflow
Approving and adopting authorities are now calling for well-designed, multifunctional SuDS with flow controls on developments. Designed specifically for SuDS, Controflow flow control chambers, inlet/outlet and erosion-control baskets, provide low-cost, passive operation solutions.
Sustainable drainage systems (SuDS) to manage rainwater are now requirements for many developments, approved and often adopted by local authorities, with technology now well-established in the UK. SuDS are essential in the fight against flooding and pollution – particularly with overloaded sewers, urbanisation and climate change – but should also offer multifunctionality and other benefits including amenity and biodiversity.
Essential Flow Controls
Increasingly, approving and adopting authorities are calling for well-designed, multifunctional SuDS on or near the surface with flow controls. For example, The Welsh Standards say: ‘The SuDS approach mimics natural drainage, managing surface runoff at or close to the surface and as close to its source as practicable, controlling the flow (volume and rate of runoff) and providing a range of additional benefits’. This approach has been demonstrated to cost less than conventional piped drainage, requiring no dedicated land-take for storage.
The key to successful design is water storage strategically deployed around a site within SuDS elements, such as green/blue roofs, swales, basins, ponds and permeable paving, forming discrete sub-catchments. Essentially, each sub-catchment should have a small orifice flow control to manage greenfield runoff rates. With their low cost and shallow construction – no more than 1.2m deep – Controflow chambers can be used more widely and wherever needed, to optimise flows from each sub-catchment, as well as at the site perimeter, while realising a key aim of SuDS to keep water management on or near the surface.
Controflow SuDS baskets simplify inlets, outlets and erosion control for SuDS.
They can also maximise storage in permeable paving on sloping sites, with terraced compartments separated by simple check dams. And they can detain water to optimise ground infiltration, so reducing discharge volumes. Importantly, SuDS techniques using Controflow chambers avoid the additional land-take and costs of large, heavily engineered control and storage structures at the edge of developments.
All orifice flow controls should be protected to prevent debris from entering the chamber. To achieve this, Controflow SuDS Baskets for filling with stone act as attractive inlets or outlets that protect pipe openings and flow control orifices, or as erosion-control to enable gentle water flows down slopes. The baskets are manufactured in stainless steel mesh and supplied with all the components for quick assembly on site. Importantly for biodiversity, Controflow chambers, inlet and outlet baskets – together with short pipe connections – reduce the risk of wildlife mortality dramatically.