Case Studies

Case Studies

Case Studies

Maida Vale, London CCTV survey of London Trunk Sewers

Maida Vale, London CCTV survey of London Trunk Sewers

Sewer Surveys UK Ltd and NHTB Consultancy worked in partnership on a Flood Risk Study for Optimise (AMP5 framework provider for Thames Water). The mission was to ascertain the reason for the many flooding incidents in the district of Maida Vale. During heavy rainfall the sewers were surcharging and in turn flooding the basements of properties in the area. It was the job of Sewer Surveys UK Ltd to find out why the basements were flooding.

To capture the data and determine the reasons for the flooding we had to get in deep to the main trunk sewers that all the properties discharged directly into. This was a challenge in itself with the bustling environment Maida Vale is, side entry manhole chambers, deep and fast flowing sewers and also large diameter trunk sewers.

We surveyed almost 4,000m of London trunk sewers with remote CCTV survey equipment and floating CCTV equipment with pan and tilt facility, the sewers ranged from 300mm concrete pipes and brick egg sewers to 3000mm circular bricksewers. To accomplish most of the surveying we had to set the CCTV equipment up within the sewers due to tight access and side entry chambers, this meant carrying out confined space entry into the sewers.

Having completed the surveys we discovered that the majority of non return valves on all the lateral connections were seized open due to wear and rust on the valves, it was this that was causing the sewers to back up through each open lateral leading to the flooding of basements.

A full CCTV survey report was produced using Wincan V8 with an AutoCAD plan showing the route of the sewers and the flow directions. The job was completed over 2 days and 2 night shifts with minimal disruption to residents and businesses in the area.



Filton Abbey Wood, Bristol CCTV Survey, Isolation of Watercourse, Tankering and Jet Cleaning of Siphon Culvert

Sewer Surveys UK Ltd and Bridgeway Consulting worked in partnership to carry out a CCTV inspection survey of a siphon culvert that runs directly under the Great Western Main Line railway between London and Bristol.

Due to the location of the culvert being next to a railway and the Inlet and Outlet both being on the public highway, our first mission was to gain safe access to the culvert, we achieved this by using our PTS trained staff and removing some of the fencing between the railway and the public highway. The siphon was a 300mm diameter concrete pipe which was approx 40m in length but from the Inlet there was a drop of approx. 10m under the railway before it climbed back up to the Outlet, this resulted in a large volume of water standing within the siphon. This culvert had not been surveyed for many years so experience told us that the siphon would probably contain debris and silt at the bottom.

Firstly, we had to isolate the watercourse of any incoming flows and pump out the water within the siphon using a large volume tanker. Once the siphon was empty of water we carried out a CCTV survey to the bottom, only at this point did we visually identify approx 30% of silt and debris. Secondly, following on from our CCTV Survey we had to clean out the bottom of the siphon, to do this we used high pressure water jetting with the jetting unit and suction facility. Once the cleaning was completed, we carried out a further CCTV survey and achieved a full survey of the siphon.

The survey, isolation of the watercourse, tankering and jet cleaning was all safely completed within 2 days with no disruption to the railway and no flooding or pollution incidents.



Ripple Brook Culvert, Southend South Station CCTV survey using Kayak of Network Rail/London Underground Culvert

Ripple Brook Culvert, Southend South Station CCTV survey using Kayak of Network Rail/London Underground Culvert

Sewer Surveys UK Ltd and Bridgeway Consulting worked in partnership to carry out a CCTV inspection survey of a heavily silted culvert that runs directly under the Network Rail and London Underground.

The culvert is a brick arch with a natural invert and is approx 75m in total length with a 45 degree bend half way through. The initial enquiry was to carry out a CCTV inspection survey of the culvert with has good access from a car parking area. The culvert was approx 3000mm wide and 2000mm high. On arrival at the site we discovered that the culvert was 50% full of silt and using the CCTV equipment we were able to zoom in almost 50m and found that the silt carried on all the way through. We achieved no survey with the CCTV equipment. On our second visit to the site we took a full man entry confined space entry team supported by a rescue team on standby, this was almost fruitless as the gas detectors alarmed just 6m into the culvert. Due to the thickness of the silt we were struggling to walk through the culvert even with full breathing apparatus. This culvert required surveying urgently and with cleaning the culvert not an option at this point we had to come up with a method to complete a survey of the culvert somehow?

Our answer...

We decided to strap the CCTV equipment to a Kayak, and to also strap a high pressure jetting nozzle fed from a jetting machine to the bottom. When we powered the jetting nozzle it created rear facing pressure which pushed the Kayak through the culvert and floated over the silt. We managed to survey the entire culvert at a moderate speed using this method.

A full structural report was issued to the client on completion.


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