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Road drainage and gullies

Who is responsible for the different parts of the drainage system? How to report blocked missing or smelly gullies.

Road drain

Unfortunately there are lots of different organisations involved in managing different parts of the drainage system. 


Most common feature is a gully. This consists of a concrete pot positioned under the road surface with an iron grate visible from the road. The water collects in the concrete pot and is then channeled through a series of pipes before connecting into the surface water sewer network or to a soak away. 

New road gully Sometimes these pots and channels become blocked with soil, dead leaves and rubbish, preventing the free flow of water to the main surface water sewer. Clearing debris by washing it into gullies can also contribute to the problem, as well as causing water pollution.

Hillingdon Council have over 36,000 gullies across the borough, and these are cleared every year. Gullies are normally cleaned by lifting the metal grating or cover and sucking all the dirt out using a gully sucker machine. Sometime jetting is required to move some of the obstructions. Most gullies are designed to trap smells coming back up from the pipes but in very dry weather they can dry out and allow smells to escape.

There are also private roads which have gullies or other road drainage which are the responsibility of those residents to maintain.

Surface water sewers

The water flows from a gully into a surface water sewer main. Often flooding can occur even where the gully is clear. This can be because there is a blockage within the surface water sewer, for example because of tree roots or silt build up, a blockage at the outfall or as a result of the river levels being high.

Surface water sewers are the responsibility of the utility companies, and in Hillingdon, this is Thames Water. The utility company will investigate and determine if there is an issue and take appropriate action to clear it.

If a water main is overwhelmed simply because a great deal of rain has fallen, a utility company is not required to undertake works to increase the size.

Flooding on roads

New roads include designed drainage systems intended to remove water efficiently from the surface of the highway to provide a safe passage for all vehicles and pedestrians. Older roads may have less sophisticated drainage, but all have features designed to take the water away from the road surface. In some rural areas or on very minor roads, this may simply be a ditch leading to a watercourse.

When there is very heavy rain arriving on the highway in a short period it can often be greater than the capacity of the drainage facilities designed to take it away, so it should be expected to see some water on a road after very heavy rain. Roads are designed to contain this water on the road by keeping it within the kerbs.

So despite the work undertaken by the different organisations there can be flooding on the roads. Please allow some time to see if the water drains away, water can remain for a while in low spots in the road even where the drainage system is working.

However if the water remains after a number of hours, the gullies and the sewers may need to be investigated by the different organisations in order to determine if there is a problem or if the drainage system does not have the capacity in it.

If you know it's a gully and have seen a flood on a road that's not clearing up, please report it to the council.

Blocked gully
Damaged/missing gully cover
Ditch clearing or other maintenance

Please bear in mind it may be the surface water sewer that has caused the gully to block up, and this will need to be reported to the utility company to investigate. 

If you are aware it is the surface water sewer that is blocked

Report sewer issue online to Thames Water or call on 0800 0093964 - please select option two.

If you have been affected by the water building up on a road and then flooding your home, you will need to report it to Thames Water, (the council have been advised by Thames Water that this cannot be done by the council on residents behalf). In order that your flooding is properly registered by Thames Water and given the appropriate priority within their future programme of works, you will need to fill in the Thames Water Sewer Flooding Questionnaire [51KB].

Residents may wish to take other action themselves to prevent water from draining to the sewer by putting in water butts, or ensuring their front garden remains permeable as well as putting in place flood protection measures.

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Article utilities:  Bookmark and Share Print Print this page Last updated: 09 Apr 2018 at 09:03