Swales - Technical Information

Dry or enhanced swales

Where there is insufficient space available, the swale system depth is typically limited due to the proposed location (i.e. adjacent to a vehicle trafficked area), or a deep inlets needs to be integrated into the swales.

Where the swales surface channel has a permeable base, an under drained (also known as ‘dry’ or ‘enhanced’) swale may be installed, with a layer of filter material installed below it. The filter material would typically include a conduit to encourage water flow to the downstream discharge point, into which, deep inlet pipes may also be incorporated. Where a below ground conduit receives direct inflows (i.e. via pipe connection), careful design of the overlying medium or control features would still allow the surface channel to provide attenuation storage during high rainfall events.

The depth of the permeable base construction may be increased to achieve a corresponding increase in the total storage capacity of the system; without a corresponding increase in land take, or increase in landscaped depression depth, which would normally be associated with increasing the capacity of typical conveyance swales.
 

Increasing storage in swales - hydraulic benefits

Enhanced swales can be achieved by increasing the diameter of the perforated Ridgidrain pipe or substituting the pipe with a geocellular unit which would still allow flows along the swale (behaves like a conduit). 

Polypipe is able to offer a wide range of thermoplastic pipe systems, including a comprehensive range of pipe diameters and fittings, allowing simple integration into the drainage system. Where the hydraulic capacity of the swale has been increased through the provision of a granular filter layer below the swale invert (i.e. dry or enhanced swale), additional attenuation storage capacity may be provided by oversizing the conduit pipe which is typically installed within the granular layer.
 

Swales Features and Benefits

·      Pollution and blockages can be dealt with easily

·      Removes urban pollutants

·      Easy to incorporate into landscaping

·      Maintenance can be incorporated into general landscape management

·      Low cost