Civil Engineering


Balancing Pond Clearance

Collaboration by Survey, Civils and Remediation Teams

Carnell teams from various disciplines worked together to survey and clear three balancing ponds in the National Highways East Midlands area, restoring their full capacity and improving the resilience of the network, leading to safer journeys for customers. Techniques including using innovative amphibious machines and excavators removed 1200 tonnes of silt and vegetation from the detention ponds located on the A6 Alvaston & A46.

The scheme started some months prior to the construction phase, with asset management surveys (GPS and CCTV) carried out on several balancing ponds in the East Midlands. These investigations were carried out by our Drainage Surveys team and identified the ponds that were most in need of attention, providing information to develop the 3d process.

Working Days and Minimising Delays

National Highways instructed our Civils team to remove the silt and vegetation which had accumulated since their construction, retaining some vegetation to ensure a balance between providing ecological value and drainage function.

Due to heavy rainfall and to avoid delays that would take the programme into the nesting season, Carnell carried out the work while the ponds were full, sourcing aquatic plant to make this possible.

Once completed, our Remediation team jetted the pipework so that it was no longer holding water and carried out post-remediation surveys for updated condition data and upload to DDMS.

Originally programmed for night works, Carnell established off-network access to enable day time working which led to several benefits…


  • Reduced risk of slips trips and falls by having greater visibility of the undulating ground.
  • This contributed to a zero AAFR (all accident frequency rate) on the scheme.
  • Improved visibility allowed the ecologists to complete surveys more thoroughly following environmental near misses on similar schemes by other delivery partners.
Customer Service
  • Reduced disruption from construction noise and lighting for the landowner (who lives on the property), nearby residents and road users.
  • Improved liaison with the landowner during the day.
  • Better control of pedestrians and cyclists as visibility is far greater and the perception that the site team are more approachable during daylight hours.
  • Efficiency savings of £42,960 (endorsed by the NH Efficiencies Manager), as operating during opening hours of waste facilities, provides better use of wagons on turnaround and reduces costs.
  • Improved communications between the site team and project team / NH when working during office hours. Issues can be dealt with immediately.
  • Use of de-watering plant more than doubles the amount of silt that can be loaded into wagons.