Topographical & bathymetric surveys at Hobhole Bank pumping station, Lincolnshire

Survey Solutions was asked to carry out a full topographical and bathymetric survey of the pumping stations and channels at Hobhole Bank, to enable the client to progress with design work on a new pumping station. The pumping stations control the output of water from the Hobhole Drain into the tidal river Haven.

The tidal mudbanks of the channel flowing from the pumping Station to the main river needed to be surveyed in detail, but accessing these to survey required a variety of survey methods to be employed. A large area of land surrounding the pumpstation and channels was also required to be surveyed.

For the majority of the site, traditional survey methods were able to be employed, with control established using GPS. This aspect of the survey was completed by a team of surveyors working with total stations and GPS to cover the large site area in four days of onsite work.

The steep banks down to the Hobhole Drain meant that levels close to the water and along the channels edge would need to be recorded remotely, using the reflectorless capability of the total stations. This also enabled us to record channel details on the west side of the channel which was not open to direct access due to dense vegetation cover on the steep bank.

The Hobhole drain as it leads into the older diesel, and the newer electric pumping stations were measured using a dingy with an echosounder attached. This enabled a dense grid of bed levels to be recorded, which could then be combined with the topographical data measured from the bankside. To measure the levels of the concrete base at the screened inflow into the pumping station, the survey team in the boat employed an extended pole that could reach down to 5m, and be pushed through the sediment to the hard concrete below.

On the seaward side of the site, the survey team worked with the tides, using low tide when the mudbanks were exposed to record levels across much of the mudbanks with the remote reflectorless capability of the total stations. At high tide, the boat and echosounder were employed to grid the channel flowing from the pumpstation to the main river channel.

Combining these methods resulted in a dense coverage of survey points that accurately recorded the channel bed. All the survey data was then collated to produce a single survey model, from which a 3D digital terrain model could be produced, and the survey outputs that the client required were then outputted from this.

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