Grand Union Canal – Hydrometric survey

Location: Grand Union Canal
Client: Affinity Water, Severn Trent Water, Canal and River Trust


Water companies in England and Wales are currently investigating a wide range of Strategic Resource Options (SROs) to address the long-term challenge of providing resilient, sustainable sources of potable water in the face of the challenges of climate change, population growth and the need to reduce unsustainable abstractions. One of these SROs under consideration is to use the existing infrastructure of the Grand Union Canal to transfer treated effluent from Birmingham to the Affinity Water central supply area which forms a ring around the west and north of London. The project is being developed collaboratively by Affinity Water, Severn Trent Water and the Canal and River Trust. We are commissioned to undertake hydrological, hydraulic and water quality modelling of the transfer, along with hydrometric and topographic surveys of the canal and connected watercourses. Here, Senior Surveyor John Gaskell introduces the hydrometric surveys.


The project involved working with our client Affinity Water to carry out hydrometric monitoring.

The aim was to verify and improve a water resources model and a hydraulic model of the potential Grand Union Canal (GUC) SRO transfer route between Birmingham and Hertfordshire/Bedfordshire. In order to understand the relationship between the canal level and spillway weirs, spot flow measurements were required at canal feeders and spills along with continuous levels on some key pounds for a period of 2 months.

We used the River Surveyor M9 Acoustic Doppler Current Profiler (ADCP) to provide accurate and efficient flow measurement, whilst also minimising risks to our survey teams. There are further benefits of this approach:

  • An intelligent algorithm analyses water depth, velocity and turbulence, and then acoustically adapts to those conditions so can be used in all water conditions.
  • Allows for the clearest velocity picture possible with cell sizes down to 2 cm.
  • Has a depth range of between 0.02m to 15m so can be used in shallow water and deep waters.
  • Using Sontek’s River Surveyor Live software we can see on-the-fly depth and flow data in real time.

The Team

Jon Gaskell and Rebecca Crowther have been carrying out the flow gauging on the southern end of the canal alongside subconsultant WHS on the northern end. The ADCP boat was rented from UKCEH, who also provided bespoke training in its use in low velocity situations such as canals.


Using the Sontek River Surveyor provided several key benefits to the project, compared to the more traditional hand-held spot gauging:

  • The ability to take flow readings at any canal cross-sections eliminated the need for the surveyors to directly access structures such as overflow weirs which might require access across third-party land or use of boats or floats within the canal.
  • As well as improving safety, this also meant that a greater number of sites could be gauged each day as sites could be easily accessed from the canal tow-path.
  • Even where weirs were accessible, the flow over them was sometimes too shallow to accurately gauge with hand-held velocity profilers, whereas accurate flow gaugings could be obtained from the canal channel itself.

Our hydrologists are now starting to apply the results to calibrate the hydrological model of the canal system. This in turn will allow an accurate analysis and assessment of the proposals to use the GUC as a strategic water resource transfer route, in response to increasing population growth and risks from future climate change.

Want to know more?

For more information about this project please contact Paul Eccleston.

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