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Clearway and Safeicurb

General principles

The aim is to ensure prompt and cost-effective removal of surface water during and immediately after rainfall.

Optimum balance of cost efficiency and performance is achieved by parallel drainage runs at 30-35m intervals across drainage area.

Wider spacing between runs is possible, but (dependent on rainfall intensity) may result in slower removal of surface water and increased costs – for extra outlets and additional underground pipework.

Maximum recommended width of the drained area to any one run is 35 metres.

Choose slot or grid unit options according to type and frequency of anticipated trafficking. While these options do not affect the design of drainage performance, the choice of nominal bore (Safeticurb 125mm or 150mm; Clearway 150mm only) does affect capacity and self-cleansing capability.

Self-cleansing velocity

A flow rate of 0.76 metres per second is normally sufficient to avoid silt settlement in the channel inverts. Longitudinal gradients required to achieve this velocity are: for 125mm bore (Safeticurb only): 0.75% (1:133) for 150mm bore (Clearway or Safeticurb) 0.60% (1:167).

Both systems will operate successfully at slacker gradients, though occasional flushing out may be needed.

System drainage areas: Gradient against rainfall intensity by nominal bore

* Safeticurb only