Selecting the Right Flow Control for the Job
Controflow® products are specifically designed for all types of shallow SuDS elements with low flow rates, whether new-build or retrofit.
Level or Stepped Inverts?
If the discharge route for runoff is through a series of ‘green infrastructure’ features at or near the surface – like filter strips, filter drains, swales, basins, wetlands, ponds and bioretention raingardens – then flow controls will need to be shallow, accessible and restrict flows to low flow rates. A level invert arrangement is needed so that inlets into subsequent SuDS features are above final storage levels to maximise storage in open SuDS features and reduce risk to people using the SuDS landscape.
Where the discharge route is to the storm sewer or combined sewer – particularly in SuDS retrofit – and the sewer is significantly below the adjacent construction surface, then a stepped invert should be selected to provide cover and avoid unnecessary encasement of pipe outlets to the sewer system.
Guarded or Unguarded Orifices?
All openings in drainage systems are at risk from blockage irrespective of the size of the opening. However, Controflow orifice openings regularly go down to 10mm and in more than 20 years there has not been one report of blockage.
Permeable paving and filter drains themselves provide complete upstream protection to the flow control orifice and orifice guards are therefore unnecessary. In contrast, open ‘green infrastructure’ features rely on a combination of vegetation to trap debris that is heavier than water, including silt, and Controflow SuDS Baskets with stone fill help to prevent floating debris entering the flow control chamber. In addition, flow controls with an integral upstream orifice guard are recommended.
