Vehicles on our roads generate many contaminants e.g. from tyre and brake wear and engine exhaust. This material settles on the road surface and is washed into the road channels and catchpits. 

The catchpits have sumps in them to trap the debris and particles washed off the road surface. The outlet pipe is above the sump in the bottom of the catchpit and traps the debris and pollutants. Regular cleaning of the sump is essential to prevent contaminants washing down stormwater pipes and ending up in our streams and on our beaches.