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Highway Drainage

One of our roles as a designated Highway Authority is to ensure Cardiff’s roads are built and maintained to a suitable standard, this includes the maintenance of highway drainage. 

Highway drainage systems are installed to collect surface water run-off to:

  • ​alleviate flooding, 
  • protect the construction of the highway, and 
  • retain a safe surface for vehicle movements.

Roads are designed so that water drains away from the surface to the edge and is collected by highway drainage systems. The types of drainage systems used depend on where the road is and what has been put in place.

Highway gullies, you may call them drains, are drainage pits covered by an open metal grating, typically located at the edge of the highway, often next to the kerb edge. 

The purpose of a highway gully is to drain rainwater from the highway into a sewerage system (pipe system). 

Once the water has entered the sewerage system it is conveyed to a discharge point, typically a surface water sewer or watercourse. 

We maintain these gullies by operating a system of scheduled and emergency gully cleansing. In times of high leaf fall, we also attempt to keep the roads clear of leaves blocking the gullies. 

There are a number of reasons why gullies can stop working and we are always grateful for help in identifying problem gullies. Autumn is the busiest time of year for our Highways Teams as it is often difficult to keep on top of the leaf fall. During these periods, we look to sweep the roads, including a system of cleansing in areas of particular dense tree cover, but it is often difficult for us to attend sites to clear the gullies. 

Be aware of any highway gullies near your property. Remember that the highway drains are unlikely to be blocked, it is usually a covering of leaves preventing water entering a gully that causes a problem.

Look out for:

  • ​Water that is not draining away or where there is a deep pool of water on the surface of the road for a period of time after the rain has stopped (please remember that gullies should usually have some water in them).
  • Soil and other rubbish is covering the grating.
  • Metal grates and broken or badly sunken.

Report a problem

You can help by reporting any problems and by regularly sweeping away leaves that have settled on the metal gully grating. This simple action can help prevent water ponding on the road and allow it to drain away quickly, improving traffic flow.