Flooding (drainage and gullies)
A major part of the road network is the drainage system, designed to take water away from the road surface. Problems can occur even when it is clean and well maintained.
Flooded or waterlogged roads happen when the amount of water on the road is more than the road drainage can cope with.
Exceptional rainfall, a road being in a low lying area or changes in 'run off' water from nearby land are some of the reasons why a road might flood even though the drainage system is in good working order.
Drainage systems should work without any routine maintenance, although we do normally empty gullies to remove silt.
Gullies after downpour
Drainage gullies and drains can become blocked very quickly when materials like mud or stones are carried onto the road during heavy rain or flooding. This can also happen when there is a heavy fall of leaves.
Intense rainfall can overwhelm the drainage systems where water comes back up and out of the gullies and overspills onto the road, and is not always a sign of a blocked pipe or that a gully is jammed full of silt and debris. A rule of thumb is that after an hour of so of the intense rainfall ending, the puddle/flood should have receded from the road surface and the gully should appear to be working normally.
Risk-based approach to gully cleaning and setting cleaning frequencies
Across the county we have nearly 130,000 gullies and kerb weirs. Traditionally these have been inspected (at least once every two years) and cleansed on a routine basis. Over the last 5 years we have been collecting data about their condition and location and have now moved to what we refer to as a ‘risk-based approach’ to gully cleaning. Effectively each gully is set its own risk level based on a scientific model using the following data and flooding considerations:
- Four years of silt level data (2014/15-2018/19) from routine & emergency cleansing works undertaken
- Speed limit and accident data for A & B roads
- 1 in 30 Flood map for surface water
- 1 in 100 Flood map for surface water
- 1 in 1000 Flood map for surface water
- National flood zone 3
- National flood zone 2
- Digital Elevation Model Of Gloucestershire (LIDAR)
The model is very scientific but very broadly speaking the risk rating and cleaning frequencies are:
- low risk = clean the gully every 3 years (you would expect this where recorded silt levels are 0 to 25% in the gully pot and none of the other factors come significantly into play)
- low to medium risk = clean every 2 years (silt levels are 25 to 50%)
- medium to high risk = clean yearly (silt levels are 50 to 75%)
- high risk = clean twice a year (silt levels are 75% or more)
Where several gullies along a road have different risk ratings we harmonise them all to the gully with the highest rating and the same for any gullies in adjoining side roads within 15m of the main road to cover the main braking/accelerating areas.
Using this approach we can target our resources to where they will have the most positive effect i.e. clean the gullies that readily silt up more often and before the silt causes blockages in the drainage system. This in turns reduces the risk of roads and properties from flooding. We continue to collect data so that we can review and refine our approach.
This process is aimed at gullies that are filling up readily with silt and does not address the short term issues of:
- Every autumn when trees drop their leaves that often sit on top of the gullies preventing the water getting into them. This is where we ask the public to help us by removing the leaves off the gullies where safe to do so.
- Intense rainfall that simply overwhelms the drainage systems and where water comes back up and out of the gullies and overspills onto the road.
Report flooding on roads
For flooding on, or from public roads, or to report blocked gullies or gratings please use our online forms
We are responsible for maintaining and repairing drainage and culverts on land we own.
We may take action against other land owners where problems are caused on the road because of damaged drainage on their land.
If you notice flooding or can see that flooding is about to happen on a road please Call: 08000 514 514.
The district or borough council may also serve notice on riparian landowners to remove blockages to watercourses on their land. A riparian owner is someone who owns land which a watercourse or river passes through. This is defined in the Land Drainage Act 1991.
We wouldn't usually get involved in cases where flooding is caused on private property due to run-off from another private property. This is a civil matter between the two landowners.
Report other types of flooding
Flooding from public sewers
The water company own and manage the network of public foul and surface water sewers.
To report an overflowing public sewer in Gloucestershire, you should call
- Severn Trent Water: 0800 7834444
- Thames Water: 0800 316 9800
- Wessex Water: 0345 850 5959
- Welsh Water: 0800 085 3968
Flooding from a burst water main
Your local water company is responsible for the supply of water mains up to and including the water stopcock.
In the event of a burst water main, please contact your local water supply company; their number will be on your water bill, or can be found on the internet.
Flooding from a main river
The main rivers are the responsibility of the Environment Agency.
In addition, they provide Flood information service, a 24-hour advice and information service for floods and flood warning.
Flooding from watercourses, other than main rivers
Watercourses, other than main rivers, are the responsibility of riparian owners.
You are a riparian owner if your property or land is on, or very near, a watercourse.
Riparian owners have a duty to keep the watercourse clear of any obstruction to flow and we serve legal notices on riparian owners to deal with obstructions.