- Material
- Silt, sand and grit
- Common locations
- Drain runs, catchpits and culverts
- Main requirement
- Mobilise the deposit and recover it from the system
- Check afterwards
- Remaining deposits, defects and the flow route
Where silt and grit collect
Silt and grit build up where drainage receives sediment from yards, roads and working areas, especially at low points and where flow slows. The source upstream and the route downstream both matter when deciding how much of the system needs attention.
A pattern linked to rainfall or site operations can point to a continuing sediment source. Regular build-up may also indicate a drainage defect or layout problem rather than a one-off blockage.
Jetting and recovery
Jetting loosens and moves deposited material; extraction or another recovery method is needed to take it out of the drainage system. Pushing sediment into the next chamber, separator or outfall simply moves the problem.
Access, water flow, equipment reach and the volume of sediment all affect the method. Culverts and chambers may also involve confined-space or water hazards that need their own competent assessment.
Recovered silt and washwater
If recovered silt is discarded as waste, its source and possible contamination matter to its classification. Sediment from roof drainage cannot be assumed to have the same characteristics as material from a fuel-handling or industrial area.
Washwater and mobilised solids need to be contained so that contaminated water does not enter surface-water drainage or a watercourse. A current drainage plan and knowledge of the site activity are useful when deciding the recovery route.
Checking for recurring deposits
The final inspection should record the cleaned length, material that remains and any inaccessible sections. Once the route is exposed, damage or restrictions that contribute to repeated build-up may become visible; continuing sediment sources may need separate upstream controls or maintenance.