Flooding of Roads


Purpose of the note
1.            To discuss road flooding.


roads include drainage systems designed to remove water efficiently from the
surface of the highway to order to provide a safe passage for 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 some minor roads, this may simply be a ditch leading to a

Road Gullies

The most
common feature in road drainage is the gully. This consists of a concrete pot
positioned under the road surface with an iron grating visible in the road. Water
collects in the concrete pot and is then channelled through pipework before
connecting into a surface water sewer network, a soak away or into a nearby
water course. 

the gullies and pipework become blocked with soil, dead leaves and rubbish
which prevents the free flow of water. Clearing debris by washing it into
gullies can also contribute to the problem. More information can be found by searching for
water pollution on the Hillingdon website.

Who is responsible?


Council have over 33,000 gullies across the borough which are cleaned on a yearly
basis. 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 harder 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.

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

Surface water sewer network

the gulley is connected to a surface water sewer flooding can often occur even
when the gully is clear because there is a blockage within the sewer itself.
This can often be due to tree roots growing through the sewer or just a build
up of silt.  Surface water sewers
are the responsibility of the utility company, and in Hillingdon, this is
Thames Water.

utility company will investigate and determine if the water main is blocked and
take appropriate action to clear it.  If a water main is overwhelmed simply because a great deal of
rain has fallen, the utility company is not required to undertake works to
increase the size.

Flooding on roads

there is very heavy rain over a short period the surface water build up can
often be greater than the capacity of the drainage facility 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 water on the road within the
kerbs. Heavy rain over a prolonged period can also affect soakaways as the
water table for the area, particularly low lying areas, can rise making
soakaways less affective.   

Who and when to report issues

the maintenance undertaken by the Council, problems can also occur even when
drainage installations are clean and well maintained. Heavy rain can wash
leaves and other material into a gully blocking them.

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.

if the water remains after a number of hours, please report it to the Council
to investigate to see if the gully is blocked. Please bear in mind it may be
the surface water sewer that is blocked, and this will need to be reported to
the Utility Company to investigate.

If you know the issues are with a gully and have seen
flooding remain on a road for a long period, please use the following

·      COUNCIL. Please use the Council ‘Report it’ function on the
Council website in the first instance, and the maintenance team will prioritise
it against other calls. If you are concerned that it is causing an imminent
flooding issue please call the Customer
Contact Centre on 01895 556000

·      THAMES
WATER.  If you are aware it is the
surface water sewer that is blocked:

Report it via Contact us on their
website or call Thames Water on 0800
then please select Option 2

Specific issues raised

462 Bath Road, Longford and Meadowlea
Close, Harmondsworth

concerns have been reported to the Highways Maintenance team, who have checked
the drainage system and ensured it is clear. The limiting factor in reducing
the frequency of flooding is that the gullies drain to a Thames Water surface
water sewer over which the Council has no control.

Candover Close Bus Stop

concern has been reported to the Highways Maintenance team, who have checked
the drainage system and ensured it is clear.

Action residents can take

the increasing demand on the capacity of surface water sewers and the situation
where the water company will not increase the capacity of the sewer there is
action residents can take to reduce the likelihood of flooding affecting them
and their community. This can be by putting in water butts or rainwater
harvesting in order to control surface water and reuse it on the their property,
and ensuring their front garden remains permeable. There is a legal requirement
to ensure that front gardens where people wish
to use them as driveways don’t contribute to flooding.