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Highways information [v]

Information on your highways.

Overview

We have an extensive asset of highway drainage, including:

  • nearly 130,000 gullies;
  • 24 balancing ponds;
  • 2603m of main culvert;
  • 70,000 grips;
  • 90 cattlegrids; and
  • 93,363 manholes - all of which is serving the county's roads.

The team are also working to improve the Drainage Inventory by collating drainage asset data on site flooding hot spots and problem areas.  This is vital asset information which will help us improve and plan our surface water management in the future. The team works closely with GCC’s Flood Team and respective Land Drainage colleagues at the District/Borough Councils, the EA and water utilities. 

GCC’s Flood Team

As a Lead Local Flood Authority, under the Flood and Water Management Act 2010, the GCC Flood Team has responsibilities for:

  • investigating and reporting flooding incidents
  • managing flood risk from surface water, groundwater and ordinary watercourses (i.e. non main rivers)
  • producing a local flood risk management strategy
  • consenting works on ordinary water courses
  • enforcing works to maintain the flow on ordinary water courses.

Highways - Risk-based approach to gully cleaning and setting cleaning frequencies

Across the county we have nearly 130,000 gullies & 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 it’s own risk level based on a scientific model using the following data and flooding considerations:

Data

  • 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

Flooding considerations 

  • 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 & refine our approach.

Of course, 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 of the gullies and overspills onto the road.
  • overspills onto the road 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.

Land drainage and flooding

We are often drawn into other flooding issues on the highways that are not our responsibility. GCC is 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.  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.

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 you should call the respective water utility.

  • 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.

  • The Geotechnical programme covers landslips and subsidence that has damaged or threatens to damage highway assets (roads, footways, bridges, drainage etc) and the engineering schemes to put right the damage and prevent future occurrences.
  • We actively monitor sites where we know the ground is moving to manage the risk to the public:
  • Sometimes movement in the ground is obvious - landslips causing sections of road to collapse.
  • Sometimes movement is minimal – minor cracking or subtle deformation in the road surface.
  • Often movement is ongoing, and sites can be managed by repeatedly resurfacing, although this does not address the principal cause.

Impact of landslips

Typically we think of land slips being a dramatic event where the land and road slips down the hillside. Whilst this happened at our site at B4058 Horsley in December 2013, the reality is often significant subsidence leaving a step or a crack in the road surface which is a danger to passing traffic and damages utility services (drains, water / gas mains, electricity / phone cables etc). 

In most cases the road has to be closed to protect the public from using the road whilst there is the chance of the road slipping again, or at very least temporary traffic signals and road cones are used to direct traffic onto the side of the road that is deemed to be ‘safe’.

Page updated: 18/10/2021 Page updated by: GCC

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