Cut-off drain

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A cut-off drain can be used to intercept fast flowing water on sloping paths without introducing a wide open gap, like a cross drain or a raised step, like a water bar, in the path surface. This means that they are suitable for creating ‘barrier-free’ access without a trip hazard or a hazard where a horses foot may become trapped, then damaged or broken.

Most cut-off drains have a u-shaped cross-section and grating over the top. The grating provides a continuous surface across the drain, and should be strong enough to withstand the load of any traffic that is expected to use the path.

A cut off drain can either be constructed on site using wood or, preferably, made from sections of ‘linear drain’. These prefabricated units are more robust and have a longer life span. They are available in a range of sizes (from 50-250mm deep) and come with tightly fitting gratings. The channel unit can be made from HDPE plastic, pre-cast concrete, polymer concrete or stainless steel, with galvanised steel or HDPE plastic gratings. Linear drains used for this purpose can either have a channel with constant depth or ‘built-in’ fall (where one end is deeper than the other). For use as a cut-off drain, the constant depth type is suited to paths with a crossfall.

Linear drains are available in six 'load classes’ that comply with the European Standard DIN 19580, for intended specific purposes - class A 15kN and class B 125kN are suitable for paths. They need to be laid in a concrete bed so are difficult to retrofit without major construction works.

Cut-off drain

 

Specification
Install Class B polymer concrete linear drain (constant depth type) on 100mm concrete bed and at an angle to the path line of between 45° - 60°. Ensure that the drain has a crossfall towards the outlet side
Install Class B galvanised grating, 3mm - 5mm below the finished level of the path surface
Extend drain length by 300mm on each path verge
If required, include a large flat stone to act as a splash plate at the outlet end to prevent erosion of the path edge or a silt trap to collect washed off surface material

 

Maintenance
Inspect drain channel frequently to ensure it has not become blocked with debris - leaf litter and silt are a particular problem. It may be necessary to remove the grating in order to inspect the channel properly
If installed, inspect the outlet silt trap and remove any material annually (or after extreme weather events) – washed out surfacing could be reapplied to the path if it is relatively free from other debris

 

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