In March 2017 we were commissioned by Barhale/Thames Water to locate, measure, map and provide isolation plates for their four inlet pipes located in a 16 metres deep section of the reservoir.
We adapted a work-class PIV to house our low frequency side-scan sonar system to work effectively at medium range speeds (2-4 knots) and with the sonar scale set to 40 metres we found the twin pipelines within a couple of hours, we then narrowed the range to 10 metres and focused on a detailed asset survey.
The high level of detail obtained from the inlet pipe measuring and mapping sonar imaging allowed us to estimate the silt level around each inlet, along with any potential hazards likely to be encountered during the subsequent diving operation.
We marked each inlet with a longitude / latitude coordinate allowing repeatable visits to each location without the use of marker buoys.
Contouring the reservoir depth gave us vital information for implementing a safe dive-plan for the installation of the secondary isolation seals.
Once on location, our dive team set about cleaning mussel growth from around the inlets and then carried out an accurate survey of each one to determine the precise dimensions for the fabrication of the secondary isolation seals.
The Isolation seals were designed and fabricated in house to a very fine tolerance and were manoeuvred into position on site utilising an ‘A’ frame and lifting winch was set up on the dive support pontoon.